Emerging Research in Plant Cell Biology
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Tissue-specific silencing of Arabidopsis thaliana SUVH8 by miR171a star

Abstract

MicroRNAs (miRNAs) are produced from double stranded precursors, from which a short duplex is excised. The strand of the duplex that remains more abundant is usually the active form, the miRNA, while steady-state levels of the other strand, the miRNA*, are generally lower. The executive engines of miRNA-directed gene silencing are RNA-induced silencing complexes (RISCs). During RISC maturation, the miRNA/miRNA* duplex associates with the catalytic subunit, an AGO protein. Subsequently, the guide strand, which directs gene silencing, is retained, while the passenger strand is degraded. Under certain circumstances, the miRNA*s can be retained as guide strands. MiR170 and miR171 are prototypical miRNAs in Arabidopsis thaliana, with well-defined targets. We found that the corresponding star molecules, the sequence-identical miR170* and miR171a* have several features of active miRNAs, such as sequence conservation and AGO1 association. We confirmed that active AGO1-miR171a* complexes are common in A. thaliana and that they trigger silencing of SUVH8, a new miR171a* target that was acquired very recently in the A. thaliana lineage. Our study demonstrates that each miR171a strand can be loaded onto RISC, with separate regulatory outcomes.


Via Biswapriya Biswavas Misra
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Emerging Research in Plant Cell Biology
A science editor's take on what's new and interesting in the plant kingdom.
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BMC Biology: Genome sequencing of the staple food crop white Guinea yam enables the development of a molecular marker for sex determination (2017)

BMC Biology: Genome sequencing of the staple food crop white Guinea yam enables the development of a molecular marker for sex determination (2017) | Emerging Research in Plant Cell Biology | Scoop.it

Background. Root and tuber crops are a major food source in tropical Africa. Among these crops are several species in the monocotyledonous genus Dioscorea collectively known as yam, a staple tuber crop that contributes enormously to the subsistence and socio-cultural lives of millions of people, principally in West and Central Africa. Yam cultivation is constrained by several factors, and yam can be considered a neglected “orphan” crop that would benefit from crop improvement efforts. However, the lack of genetic and genomic tools has impeded the improvement of this staple crop.

 

Results. To accelerate marker-assisted breeding of yam, we performed genome analysis of white Guinea yam (Dioscorea rotundata) and assembled a 594-Mb genome, 76.4% of which was distributed among 21 linkage groups. In total, we predicted 26,198 genes. Phylogenetic analyses with 2381 conserved genes revealed that Dioscorea is a unique lineage of monocotyledons distinct from the Poales (rice), Arecales (palm), and Zingiberales (banana). The entire Dioscorea genus is characterized by the occurrence of separate male and female plants (dioecy), a feature that has limited efficient yam breeding. To infer the genetics of sex determination, we performed whole-genome resequencing of bulked segregants (quantitative trait locus sequencing [QTL-seq]) in F1 progeny segregating for male and female plants and identified a genomic region associated with female heterogametic (male = ZZ, female = ZW) sex determination. We further delineated the W locus and used it to develop a molecular marker for sex identification of Guinea yam plants at the seedling stage.

 

Conclusions. Guinea yam belongs to a unique and highly differentiated clade of monocotyledons. The genome analyses and sex-linked marker development performed in this study should greatly accelerate marker-assisted breeding of Guinea yam. In addition, our QTL-seq approach can be utilized in genetic studies of other outcrossing crops and organisms with highly heterozygous genomes. Genomic analysis of orphan crops such as yam promotes efforts to improve food security and the sustainability of tropical agriculture.


Via Kamoun Lab @ TSL
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Beyond editing to writing large genomes

Beyond editing to writing large genomes | Emerging Research in Plant Cell Biology | Scoop.it
Recent exponential advances in genome sequencing and engineering technologies have enabled an unprecedented level of interrogation into the impact of DNA variation (genotype) on cellular function (phenotype). Furthermore, these advances have also prompted realistic discussion of writing and radically re-writing complex genomes. In this Perspective, we detail the motivation for large-scale engineering, discuss the progress made from such projects in bacteria and yeast and describe how various genome-engineering technologies will contribute to this effort. Finally, we describe the features of an ideal platform and provide a roadmap to facilitate the efficient writing of large genomes.

Via Loïc Lepiniec
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Global climatic drivers of leaf size

Global climatic drivers of leaf size | Emerging Research in Plant Cell Biology | Scoop.it
Why does plant leaf size increase at lower latitudes, as exemplified by the evolutionary success of species with very large leaves in the tropics? Wright et al. analyzed leaf data for 7670 plant species, along with climatic data, from 682 sites worldwide. Their findings reveal consistent patterns and explain why earlier predictions from energy balance theory had only limited success. The authors provide a fully quantitative explanation for the latitudinal gradient in leaf size, with implications for plant ecology and physiology, vegetation modeling, and paleobotany.

Science , this issue p. [917][1]

[1]: /lookup/doi/10.1126/science.aal4760
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Characterization of scientific studies usually cited as evidence of adverse effects of GM food/feed - Sánchez - 2017 - Plant Biotechnology Journal - Wiley Online Library

GM crops are the most studied crops in history. Approximately 5% of the safety studies on themshow adverse effects that are a cause for concern and tend to be featured in media reports.Although these reports are based on just a handful of GM events, they are used to cast doubt on all GM crops. Furthermore, they tend to come from just a few laboratories and are published inless important journals. Importantly, a close examination of these reports invariably showsmethodological flaws that invalidate any conclusions of adverse effects. Twenty years aftercommercial cultivation of GM crops began, a bona fide report of an adverse health effect due toa commercialized modification in a crop has yet to be reported
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High throughput phenotyping to accelerate crop breeding and monitoring of diseases in the field.

High throughput phenotyping to accelerate crop breeding and monitoring of diseases in the field. | Emerging Research in Plant Cell Biology | Scoop.it
Highlights • Phenotyping technology can increase the throughput of plant screening in the field. • Early season detection of plant diseases is key to reducing crop yield losses. • Disease diagnosis relies on symptom recognition through observations and ratings. • Remote sensing methods can identify, quantify and monitor plant diseases. • Sensor-based phenotyping will accelerate the rate of genetic gain in crops. Effective implementation of technology that facilitates accurate and high-throughput screening of thousands of field-grown lines is critical for accelerating crop improvement and breeding strategies for higher yield and disease tolerance. Progress in the development of field-based high throughput phenotyping methods has advanced considerably in the last 10 years through technological progress in sensor development and high-performance computing. Here, we review recent advances in high throughput field phenotyping technologies designed to inform the genetics of quantitative traits, including crop yield and disease tolerance. Successful application of phenotyping platforms to advance crop breeding and identify and monitor disease requires: (1) high resolution of imaging and environmental sensors; (2) quality data products that facilitate computer vision, machine learning and GIS; (3) capacity infrastructure for data management and analysis; and (4) automated environmental data collection. Accelerated breeding for agriculturally relevant crop traits is key to the development of improved varieties and is critically dependent on high-resolution, high-throughput field-scale phenotyping technologies that can efficiently discriminate better performing lines within a larger population and across multiple environments.
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Unlocking a key to maize's amazing success

Unlocking a key to maize's amazing success | Emerging Research in Plant Cell Biology | Scoop.it
Summary
Maize grows on every continent save Antarctica and provides food and biofuels for millions of people. Now, researchers studying ancient and modern maize have found a clue to its popularity over the millennia: maize’s easily adjustable flowering time, which enabled ancient peoples to get the plant to thrive in diverse climates, according to several studies presented in July at the meeting of the Society for Molecular Biology and Evolution in Austin. The studies found hints of the genomic shifts behind such rapid change, and ancient DNA studies presented at the meeting began to clarify when maize flowering came under farmer control, revealing enormous adaptive potential that humans were able to exploit.

Via Loïc Lepiniec
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Vesicle trafficking in plant immunity

Vesicle trafficking in plant immunity | Emerging Research in Plant Cell Biology | Scoop.it

Highlights


• SNAREs are the minimal core factors to drive vesicle fusion events in plants.
• Extracellular immune proteins travel along the default secretory pathway.
• Plant surface immune receptors are endocytosed and degraded upon activated.
• Oomycete/fungal pathogens highjack the vacuole-targeted PVCs/MVBs.



To defend against extracellular pathogens, plants primarily depend on cell-autonomous innate immunity due to the lack of the circulatory immune system including mobile immune cells. To extracellularly restrict or kill the pathogens, plant cells dump out antimicrobials. However, since antimicrobials are also toxic to plant cells themselves, they have to be safely delivered to the target sites in a separate vesicular compartment. In addition, because immune responses often requires energy otherwise used for the other metabolic processes, it is very important to properly control the duration and strength of immune responses depending on pathogen types. This can be achieved by regulating the sensing of immune signals and the delivery/discharge of extracellular immune molecules, all of which are controlled by membrane trafficking in plant cells. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are now considered as the minimal factors that can merge two distinct membranes of cellular compartments. Hence, in this review, known and potential immune functions of SNAREs as well as regulatory proteins will be discussed.


Via Christophe Jacquet
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Rhamnose-Containing Cell Wall Polymers Suppress Helical Plant Growth Independently of Microtubule Orientation

Rhamnose-Containing Cell Wall Polymers Suppress Helical Plant Growth Independently of Microtubule Orientation | Emerging Research in Plant Cell Biology | Scoop.it

Although specific organs in some plant species exhibit helical growth patterns of fixed or variable handedness, most plant organs are not helical. Here we report that mutations in Arabidopsis RHAMNOSE BIOSYNTHESIS 1 (RHM1) cause dramatic left-handed helical growth of petal epidermal cells, leading to left-handed twisted petals. rhm1 mutant roots also display left-handed growth. Furthermore, we find that RHM1 is required to promote epidermal cell expansion. RHM1 encodes a UDP-L-rhamnose synthase, and rhm1 mutations affect synthesis of the pectic polysaccharide rhamnogalacturonan-I. Unlike other mutants that exhibit helical growth of fixed handedness, the orientation of cortical microtubule arrays is unaltered in rhm1 mutants. Our findings reveal a novel source of left-handed plant growth caused by changes in cell wall composition that is independent of microtubule orientation. We propose that an important function of rhamnose-containing cell wall polymers is to suppress helical twisting of expanding plant cells.

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PNAS: NLR network mediates immunity to diverse plant pathogens (2017)

PNAS: NLR network mediates immunity to diverse plant pathogens (2017) | Emerging Research in Plant Cell Biology | Scoop.it

Both plants and animals rely on nucleotide-binding domain and leucine-rich repeat-containing (NLR) proteins to respond to invading pathogens and activate immune responses. An emerging concept of NLR function is that “sensor” NLR proteins are paired with “helper” NLRs to mediate immune signaling. However, our fundamental knowledge of sensor/helper NLRs in plants remains limited. In this study, we discovered a complex NLR immune network in which helper NLRs in the NRC (NLR required for cell death) family are functionally redundant but display distinct specificities toward different sensor NLRs that confer immunity to oomycetes, bacteria, viruses, nematodes, and insects. The helper NLR NRC4 is required for the function of several sensor NLRs, including Rpi-blb2, Mi-1.2, and R1, whereas NRC2 and NRC3 are required for the function of the sensor NLR Prf. Interestingly, NRC2, NRC3, and NRC4 redundantly contribute to the immunity mediated by other sensor NLRs, including Rx, Bs2, R8, and Sw5. NRC family and NRC-dependent NLRs are phylogenetically related and cluster into a well-supported superclade. Using extensive phylogenetic analysis, we discovered that the NRC superclade probably emerged over 100 Mya from an NLR pair that diversified to constitute up to one-half of the NLRs of asterids. These findings reveal a complex genetic network of NLRs and point to a link between evolutionary history and the mechanism of immune signaling. We propose that this NLR network increases the robustness of immune signaling to counteract rapidly evolving plant pathogens.


Via Kamoun Lab @ TSL
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Aflatoxin B1 contamination in maize in Europe increases due to climate change

Aflatoxin B1 contamination in maize in Europe increases due to climate change | Emerging Research in Plant Cell Biology | Scoop.it

Climate change has been reported as a driver for emerging food and feed safety issues worldwide and its expected impact on the presence of mycotoxins in food and feed is of great concern. Aflatoxins have the highest acute and chronic toxicity of all mycotoxins; hence, the maximal concentration in agricultural food and feed products and their commodities is regulated worldwide. The possible change in patterns of aflatoxin occurrence in crops due to climate change is a matter of concern that may require anticipatory actions. The aim of this study was to predict aflatoxin contamination in maize and wheat crops, within the next 100 years, under a +2 °C and +5 °C climate change scenario, applying a modelling approach. Europe was virtually covered by a net, 50 × 50 km grids, identifying 2254 meshes with a central point each. Climate data were generated for each point, linked to predictive models and predictions were run consequently. Aflatoxin B1 is predicted to become a food safety issue in maize in Europe, especially in the +2 °C scenario, the most probable scenario of climate change expected for the next years. These results represent a supporting tool to reinforce aflatoxin management and to prevent human and animal exposure.

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Interplay of Plasma Membrane and Vacuolar Ion Channels, Together with BAK1, Elicits Rapid Cytosolic Calcium Elevations in Arabidopsis during Aphid Feeding

Interplay of Plasma Membrane and Vacuolar Ion Channels, Together with BAK1, Elicits Rapid Cytosolic Calcium Elevations in Arabidopsis during Aphid Feeding | Emerging Research in Plant Cell Biology | Scoop.it
A transient rise in cytosolic calcium ion concentration is one of the main signals used by plants in perception of their environment. The role of calcium in the detection of abiotic stress is well documented; however, its role during biotic interactions remains unclear. Here, we use a fluorescent calcium biosensor (GCaMP3) in combination with the green peach aphid (Myzus persicae) as a tool to study Arabidopsis thaliana calcium dynamics in vivo and in real time during a live biotic interaction. We demonstrate rapid and highly localized plant calcium elevations around the feeding sites of M. persicae, and by monitoring aphid feeding behavior electrophysiologically, we demonstrate that these elevations correlate with aphid probing of epidermal and mesophyll cells. Furthermore, we dissect the molecular mechanisms involved, showing that interplay between the plant defense coreceptor BRASSINOSTEROID INSENSITIVE-ASSOCIATED KINASE1 (BAK1), the plasma membrane ion channels GLUTAMATE RECEPTOR-LIKE 3.3 and 3.6 (GLR3.3 and GLR3.6), and the vacuolar ion channel TWO-PORE CHANNEL1 (TPC1) mediate these calcium elevations. Consequently, we identify a link between plant perception of biotic threats by BAK1, cellular calcium entry mediated by GLRs, and intracellular calcium release by TPC1 during a biologically relevant interaction.

Via Christophe Jacquet
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Enhanced Secondary- and Hormone Metabolism in Leaves of Arbuscular Mycorrhizal Medicago truncatula

Arbuscular mycorrhizas (AM) are the most common symbiotic associations between plant's root compartment and fungi. They provide nutritional benefit (mostly inorganic phosphate, Pi) leading to improved growth, and non-nutritional benefits including defense responses to environmental cues throughout the host plant, which in return delivers carbohydrates to the symbiont. However, how transcriptional and metabolic changes occurring in leaves of AM plants differ from those induced by Pi fertilization is poorly understood. We investigated systemic changes in the leaves of mycorrhized Medicago truncatula in conditions with no improved Pi status, and compared them with those induced by high Pi treatment in non-mycorrhized plants. Microarray-based genome-wide profiling indicated upregulation by mycorrhization of genes involved in flavonoid, terpenoid, jasmonic acid (JA) and abscisic acid (ABA) biosynthesis as well as enhanced expression of MYC2, the master regulator of JA-dependent responses. Accordingly, total anthocyanins and flavonoids increased, and most flavonoid species were enriched in AM-leaves. Both the AM- and Pi treatment co-repressed iron homeostasis genes resulting in lower levels of available iron in leaves. In addition, higher levels of cytokinins were found in leaves of AM- and Pi-treated plants whereas the level of ABA was specifically increased in AM-leaves. Treatment of non-mycorrhized plants with either ABA or JA induced upregulation of MYC2, whereas JA also induced upregulation of flavonoid and terpenoid biosynthetic genes. Based on these results, we propose that mycorrhization and Pi fertilization share cytokinin-mediated improved shoot growth, whereas enhanced ABA biosynthesis and JA-regulated flavonoid and terpenoid biosynthesis in leaves is specific to mycorrhization.

Via Tatsuya Nobori
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MicroRNAs in crop improvement: fine-tuners for complex traits

MicroRNAs in crop improvement: fine-tuners for complex traits | Emerging Research in Plant Cell Biology | Scoop.it

One of the most common challenges for both conventional and modern crop improvement is that the appearance of one desirable trait in a new crop variety is always balanced by the impairment of one or more other beneficial characteristics. The best way to overcome this problem is the flexible utilization of regulatory genes, especially genes that provide more efficient and precise regulation in a targeted manner. MicroRNAs (miRNAs), a type of short non-coding RNA, are promising candidates in this area due to their role as master modulators of gene expression at the post-transcriptional level, targeting messenger RNAs for cleavage or directing translational inhibition in eukaryotes. We herein highlight the current understanding of the biological role of miRNAs in orchestrating distinct agriculturally important traits by summarizing recent functional analyses of 65 miRNAs in 9 major crops worldwide. The integration of current miRNA knowledge with conventional and modern crop improvement strategies is also discussed.

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Frontiers | Strigolactones Biosynthesis and Their Role in Abiotic Stress Resilience in Plants: A Critical Review | Plant Science

Frontiers | Strigolactones Biosynthesis and Their Role in Abiotic Stress Resilience in Plants: A Critical Review | Plant Science | Emerging Research in Plant Cell Biology | Scoop.it
Strigolactones (SLs) being new class of plant hormones, play regulatory roles against abiotic stresses in plants. There are multiple hormonal response pathways which are adapted by the plants to overcome these stressful environmental constraints to reduce the negative impact on overall crop plant productivity. Genetic modulation of the SLs could also be applied as a potential approach in this regard. However, endogenous plant hormones play central roles in adaptation to changing environmental conditions, by mediating growth, development, nutrient allocation, and source/sink transitions. In addition, the hormonal interactions can fine-tune the plant response and determine plant architecture in response to environmental stimuli such as nutrient deprivation and canopy shade. Considerable advancements and new insights into SLs biosynthesis, signalling and transport has been unleashed since the initial discovery. In this review we present basic overview of SL biosynthesis and perception with a detailed discussion on our present understanding of SLs and their critical role to tolerate environmental constraints. The SLs and ABA interplay during the abiotic stresses is particularly highlighted.

Via Andres Zurita
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Nat. Genet.: A gene encoding maize caffeoyl-CoA O-methyltransferase confers quantitative resistance to multiple pathogens (2017)

Alleles that confer multiple disease resistance (MDR) are valuable in crop improvement, although the molecular mechanisms underlying their functions remain largely unknown. A quantitative trait locus, qMdr9.02, associated with resistance to three important foliar maize diseases—southern leaf blight, gray leaf spot and northern leaf blight—has been identified on maize chromosome 9. Through fine-mapping, association analysis, expression analysis, insertional mutagenesis and transgenic validation, we demonstrate that ZmCCoAOMT2, which encodes a caffeoyl-CoA O-methyltransferase associated with the phenylpropanoid pathway and lignin production, is the gene within qMdr9.02 conferring quantitative resistance to both southern leaf blight and gray leaf spot. We suggest that resistance might be caused by allelic variation at the level of both gene expression and amino acid sequence, thus resulting in differences in levels of lignin and other metabolites of the phenylpropanoid pathway and regulation of programmed cell death.

Via Nicolas Denancé, Giannis Stringlis
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Evolutionary routes to biochemical innovation revealed by integrative analysis of a plant-defense related specialized metabolic pathway 

Evolutionary routes to biochemical innovation revealed by integrative analysis of a plant-defense related specialized metabolic pathway  | Emerging Research in Plant Cell Biology | Scoop.it

Via Tatsuya Nobori
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Zygotic Genome Activation Occurs Shortly After Fertilization in Maize

Zygotic Genome Activation Occurs Shortly After Fertilization in Maize | Emerging Research in Plant Cell Biology | Scoop.it
The formation of a zygote via the fusion of an egg and sperm cell and its subsequent asymmetric division (ACD) herald the start of the plant's life cycle. Zygotic genome activation (ZGA) is thought to occur gradually, with the initial steps of zygote and embryo development being primarily maternally controlled, and subsequent steps being governed by the zygotic genome. Here, using maize (Zea mays) as a model plant system, we determined the timing of zygote development and generated RNA-Seq transcriptome profiles of gametes, zygotes, and apical and basal daughter cells. ZGA occurs shortly after fertilization and involves about 10% of the genome being activated in a highly dynamic pattern. In particular, genes encoding transcriptional regulators of various families are activated shortly after fertilization. Further analyses suggested that chromatin assembly is strongly modified after fertilization, that the egg cell is primed to activate the translational machinery, and that hormones likely play a minor role in the initial steps of early embryo development in maize. Our findings provide important insights into gamete and zygote activity in plants, and our RNA-Seq transcriptome profiles represent a comprehensive, unique RNA-Seq dataset that can be used by the research community.

Via Loïc Lepiniec, Saclay Plant Sciences
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A gene encoding maize caffeoyl-CoA O-methyltransferase confers quantitative resistance to multiple pathogens 

A gene encoding maize caffeoyl-CoA O-methyltransferase confers quantitative resistance to multiple pathogens  | Emerging Research in Plant Cell Biology | Scoop.it
Alleles that confer multiple disease resistance (MDR) are valuable in crop improvement, although the molecular mechanisms underlying their functions remain largely unknown. A quantitative trait locus, qMdr9.02, associated with resistance to three important foliar maize diseases—southern leaf blight, gray leaf spot and northern leaf blight—has been identified on maize chromosome 9. Through fine-mapping, association analysis, expression analysis, insertional mutagenesis and transgenic validation, we demonstrate that ZmCCoAOMT2, which encodes a caffeoyl-CoA O-methyltransferase associated with the phenylpropanoid pathway and lignin production, is the gene within qMdr9.02 conferring quantitative resistance to both southern leaf blight and gray leaf spot. We suggest that resistance might be caused by allelic variation at the level of both gene expression and amino acid sequence, thus resulting in differences in levels of lignin and other metabolites of the phenylpropanoid pathway and regulation of programmed cell death.
 

Via Yogesh Gupta
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Differences in DNA-binding specificity of floral homeotic protein complexes predict organ-specific target genes

Differences in DNA-binding specificity of floral homeotic protein complexes predict organ-specific target genes | Emerging Research in Plant Cell Biology | Scoop.it
Floral organ identities in plants are specified by the combinatorial action of homeotic master regulatory transcription factors. How these factors achieve their regulatory specificities is however still largely unclear. Genome-wide in vivo DNA binding data show that homeotic MADS-domain proteins recognize partly distinct genomic regions, suggesting that DNA binding specificity contributes to functional differences of homeotic protein complexes. We used in vitro systematic evolution of ligands by exponential enrichment followed by high throughput DNA sequencing (SELEX-seq) on several floral MADS-domain protein homo- and heterodimers to measure their DNA-binding specificities. We show that specification of reproductive organs is associated with distinct binding preferences of a complex formed by SEPALLATA3 (SEP3) and AGAMOUS (AG). Binding specificity is further modulated by different binding site spacing preferences. Combination of SELEX-seq and genome-wide DNA binding data allows to differentiate between targets in specification of reproductive versus perianth organs in the flower. We validate the importance of DNA-binding specificity for organ-specific gene regulation by modulating promoter activity through targeted mutagenesis. Our study shows that intrafamily protein interactions affect DNA-binding specificity of floral MADS-domain proteins. Differential DNA-binding of MADS-domain protein complexes plays a role in the specificity of target gene regulatio

Via Mary Williams
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Emerging Insights into the Functions of Pathogenesis-Related Protein 1

Emerging Insights into the Functions of Pathogenesis-Related Protein 1 | Emerging Research in Plant Cell Biology | Scoop.it
The members of the pathogenesis-related protein 1 (PR-1) family are among the most abundantly produced proteins in plants on pathogen attack, and PR-1 gene expression has long been used as a marker for salicylic acid-mediated disease resistance. However, despite considerable interest over several decades, their requirement and role in plant defence remains poorly understood. Recent reports have emerged demonstrating that PR-1 proteins possess sterol-binding activity, harbour an embedded defence signalling peptide, and are targeted by plant pathogens during host infection. These studies have re-energised the field and provided long-awaited insights into a possible PR-1 function. Here we review the current status of PR-1 proteins and discuss how these recent advances shed light on putative roles for these enigmatic proteins.
Trends

Recent studies have shown that plant pathogenesis-related protein 1 (PR-1) family members bind sterols. This function is responsible for antimicrobial activity towards sterol auxotrophs such as Phytophthora species. However, the link between sterol binding and the proposed broader antimicrobial function of PR-1 remains unclear.

PR-1 proteins harbour an embedded C-terminal peptide (CAPE) involved in plant immune signalling. Evidence suggests that CAPE has a signalling role that facilitates defence responses against microbial pathogens and also herbivores. The CAPE response is independent of other defence signalling pathways such as those elicited by recognised pathogen-associated molecular patterns.

The significance of PR-1 proteins during plant–microbe interactions is now realised, with a growing list of identified pathogen effector proteins that directly interact with PR-1 during infection.

Via Christophe Jacquet
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In Brief: Tracking the Bacterial Type III Secretion System: Visualization of Effector Delivery Using Split Fluorescent Proteins

In Brief: Tracking the Bacterial Type III Secretion System: Visualization of Effector Delivery Using Split Fluorescent Proteins | Emerging Research in Plant Cell Biology | Scoop.it

Tracking the Bacterial Type III Secretion System: Visualization of Effector Delivery Using Split Fluorescent Proteins

Jennifer Mach

Plant Cell 2017 tpc.17.00553; Advance Publication July 13, 2017; doi:10.1105/tpc.17.00553 OPEN


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Inhibition of RNA polymerase II allows controlled mobilisation of retrotransposons for plant breeding

Inhibition of RNA polymerase II allows controlled mobilisation of retrotransposons for plant breeding | Emerging Research in Plant Cell Biology | Scoop.it
Retrotransposons play a central role in plant evolution and could be a powerful endogenous source of genetic and epigenetic variability for crop breeding. To ensure genome integrity several silencing mechanisms have evolved to repress retrotransposon mobility. Even though retrotransposons fully depend on transcriptional activity of the host RNA polymerase II (Pol II) for their mobility, it was so far unclear whether Pol II is directly involved in repressing their activity. Here we show that plants defective in Pol II activity lose DNA methylation at repeat sequences and produce more extrachromosomal retrotransposon DNA upon stress in Arabidopsis and rice. We demonstrate that combined inhibition of both DNA methylation and Pol II activity leads to a strong stress-dependent mobilization of the heat responsive ONSEN retrotransposon in Arabidopsis seedlings. The progenies of these treated plants contain up to 75 new ONSEN insertions in their genome which are stably inherited over three generations of selfing. Repeated application of heat stress in progeny plants containing increased numbers of ONSEN copies does not result in increased activation of this transposon compared to control lines. Progenies with additional ONSEN copies show a broad panel of environment-dependent phenotypic diversity. We demonstrate that Pol II acts at the root of transposon silencing. This is important because it suggests that Pol II can regulate the speed of plant evolution by fine-tuning the amplitude of transposon mobility. Our findings show that it is now possible to study induced transposon bursts in plants and unlock their use to induce epigenetic and genetic diversity for crop breeding.
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Science: Evolution of the wheat blast fungus through functional losses in a host specificity determinant (2017)

Science: Evolution of the wheat blast fungus through functional losses in a host specificity determinant (2017) | Emerging Research in Plant Cell Biology | Scoop.it

Wheat blast first emerged in Brazil in the mid-1980s and has recently caused heavy crop losses in Asia. Here we show how this devastating pathogen evolved in Brazil. Genetic analysis of host species determinants in the blast fungus resulted in the cloning of avirulence genes PWT3 and PWT4, whose gene products elicit defense in wheat cultivars containing the corresponding resistance genes Rwt3 and Rwt4. Studies on avirulence and resistance gene distributions, together with historical data on wheat cultivation in Brazil, suggest that wheat blast emerged due to widespread deployment of rwt3 wheat (susceptible to Lolium isolates), followed by the loss of function of PWT3. This implies that the rwt3 wheat served as a springboard for the host jump to common wheat.

 

See also: Caught in the jump http://science.sciencemag.org/content/357/6346/31


Via Kamoun Lab @ TSL, Jim Alfano
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Nature Microbiology: Fungal pathogenesis: Combatting the oxidative burst (2017)

Nature Microbiology: Fungal pathogenesis: Combatting the oxidative burst (2017) | Emerging Research in Plant Cell Biology | Scoop.it

See also Marroquin-Guzman et al. The Magnaporthe oryzae nitrooxidative stress response suppresses rice innate immunity during blast disease https://www.nature.com/articles/nmicrobiol201754

 

Plants respond to microbial attack with a lethal burst of reactive oxygen species. How then, do pathogens successfully invade plants? Unexpectedly, a link between primary metabolism and suppression of plant immunity allows the rice blast fungus Magnaporthe oryzae to grow in such a hostile environment.

 

Plant-infecting fungi and oomycetes are an ever present threat to global food security — each year they destroy sufficient food to feed half a billion people1. Understanding how these pathogens infect and colonize host plants is therefore crucial if we are to develop new strategies to fight fungal diseases and improve plant health. The rice blast fungus Magnaporthe oryzae is responsible for the most devastating disease of cultivated rice, the primary staple for more than half of the world's population2. Strains of the same fungus also cause blast disease of wheat, a new disease that is currently causing a severe outbreak in Bangladesh and India3. Because of its economic significance and genetic tractability, rice blast disease has also emerged as a major model for studying the molecular and cellular basis of fungal infection2,4. Similar to many pathogenic fungi, M. oryzae has evolved highly sophisticated ways to invade plant cells and disable their defence systems.

 

One of the earliest responses of plants to microbial attack is the induction of a rapid, transient burst of reactive oxygen species5 (ROS). This oxidative burst is a potent defence reaction that will kill any unsuspecting microorganism. How can pathogens still successfully invade plant cells and contend with such high concentrations of ROS? In this issue of Nature Microbiology, Marroquin-Guzman and colleagues report that a link between primary fungal metabolism and the suppression of plant immunity enables M. oryzae to protect itself from nitrooxidative stress and maintain redox balance within living rice cells6, thereby facilitating its growth within such a hostile environment.

 

To initiate rice infection, a fungal spore adheres tightly to the rice leaf surface, germinates, and rapidly elaborates a specialized infection structure called an appressorium that is used to breach the tough outer leaf cuticle4. Once inside a host cell, the fungus develops bulbous, branched hyphae that maintain intimate contact with the plasma membrane of the living plant cell, forming a specialized biotrophic interfacial complex7. The pathogen and host then engage in an intense molecular dialogue; plant metabolism is reprogrammed to the pathogen's benefit and the host immune response is suppressed4,7. Much recent research has focused on fungal effector proteins, a highly diverse group of secreted molecules that target immune responses in the host to facilitate pathogen infection and spread8. However, fungi have clearly evolved additional ways to keep plant defences at bay. Marroquin-Guzman and colleagues identified and characterized nitronate monooxygenase (NMO) from M. oryzae, an enzyme normally used by fungal cells to protect themselves from nitrooxidative stress6. They show, however, that NMO is also required for utilization of nitrate and nitrite as nitrogen sources and for maintaining redox balance within living rice cells during pathogen colonization. The latter role of NMO is essential for pathogenicity, because it provides a novel mechanism by which the fungus can prevent elicitation of the plant oxidative burst (Fig. 1).


Via Kamoun Lab @ TSL, Bridget Barker, Steve Marek
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Golden bananas in the field: elevated fruit pro‐vitamin A from the expression of a single banana transgene

Golden bananas in the field: elevated fruit pro‐vitamin A from the expression of a single banana transgene | Emerging Research in Plant Cell Biology | Scoop.it

Vitamin A deficiency remains one of the world's major public health problems despite food fortification and supplements strategies. Biofortification of staple crops with enhanced levels of pro-vitamin A (PVA) offers a sustainable alternative strategy to both food fortification and supplementation. As a proof of concept, PVA-biofortified transgenic Cavendish bananas were generated and field trialed in Australia with the aim of achieving a target level of 20 μg/g of dry weight (dw) β-carotene equivalent (β-CE) in the fruit. Expression of a Fe'i banana-derived phytoene synthase 2a (MtPsy2a) gene resulted in the generation of lines with PVA levels exceeding the target level with one line reaching 55 μg/g dw β-CE. Expression of the maize phytoene synthase 1 (ZmPsy1) gene, used to develop ‘Golden Rice 2’, also resulted in increased fruit PVA levels although many lines displayed undesirable phenotypes. Constitutive expression of either transgene with the maize polyubiquitin promoter increased PVA accumulation from the earliest stage of fruit development. In contrast, PVA accumulation was restricted to the late stages of fruit development when either the banana 1-aminocyclopropane-1-carboxylate oxidase or the expansin 1 promoters were used to drive the same transgenes. Wild-type plants with the longest fruit development time had also the highest fruit PVA concentrations. The results from this study suggest that early activation of the rate-limiting enzyme in the carotenoid biosynthetic pathway and extended fruit maturation time are essential factors to achieve optimal PVA concentrations in banana fruit.

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