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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.
Curated by Jennifer Mach
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Structural basis of JAZ repression of MYC transcription factors in jasmonate signalling

Structural basis of JAZ repression of MYC transcription factors in jasmonate signalling | Emerging Research in Plant Cell Biology | Scoop.it

The plant hormone jasmonate plays crucial roles in regulating plant responses to herbivorous insects and microbial pathogens and is an important regulator of plant growth and development1,2, 3, 4, 5, 6, 7. Key mediators of jasmonate signalling include MYC transcription factors, which are repressed by jasmonate ZIM-domain (JAZ) transcriptional repressors in the resting state. In the presence of active jasmonate, JAZ proteins function as jasmonate co-receptors by forming a hormone-dependent complex with COI1, the F-box subunit of an SCF-type ubiquitin E3 ligase8, 9,10, 11. The hormone-dependent formation of the COI1–JAZ co-receptor complex leads to ubiquitination and proteasome-dependent degradation of JAZ repressors and release of MYC proteins from transcriptional repression3, 10, 12. The mechanism by which JAZ proteins repress MYC transcription factors and how JAZ proteins switch between the repressor function in the absence of hormone and the co-receptor function in the presence of hormone remain enigmatic. Here we show that Arabidopsis MYC3 undergoes pronounced conformational changes when bound to the conserved Jas motif of the JAZ9 repressor. The Jas motif, previously shown to bind to hormone as a partly unwound helix, forms a complete α-helix that displaces the amino (N)-terminal helix of MYC3 and becomes an integral part of the MYC N-terminal fold. In this position, the Jas helix competitively inhibits MYC3 interaction with the MED25 subunit of the transcriptional Mediator complex. Our structural and functional studies elucidate a dynamic molecular switch mechanism that governs the repression and activation of a major plant hormone pathway.

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A DEMETER-like DNA demethylase governs tomato fruit ripening

A DEMETER-like DNA demethylase governs tomato fruit ripening | Emerging Research in Plant Cell Biology | Scoop.it

In plants, genomic DNA methylation which contributes to development and stress responses can be actively removed by DEMETER-like DNA demethylases (DMLs). Indeed, in Arabidopsis DMLs are important for maternal imprinting and endosperm demethylation, but only a few studies demonstrate the developmental roles of active DNA demethylation conclusively in this plant. Here, we show a direct cause and effect relationship between active DNA demethylation mainly mediated by the tomato DML, SlDML2, and fruit ripening— an important developmental process unique to plants. RNAi SlDML2 knockdown results in ripening inhibition via hypermethylation and repression of the expression of genes encoding ripening transcription factors and rate-limiting enzymes of key biochemical processes such as carotenoid synthesis. Our data demonstrate that active DNA demethylation is central to the control of ripening in tomato.

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Expression of trehalose-6-phosphate phosphatase in maize ears improves yield in well-watered and drought conditions

Expression of trehalose-6-phosphate phosphatase in maize ears improves yield in well-watered and drought conditions | Emerging Research in Plant Cell Biology | Scoop.it

Maize, the highest-yielding cereal crop worldwide, is particularly susceptible to drought during its 2- to 3-week flowering period. Many genetic engineering strategies for drought tolerance impinge on plant development, reduce maximum yield potential or do not translate from laboratory conditions to the field. We overexpressed a gene encoding a rice trehalose-6-phosphate phosphatase (TPP) in developing maize ears using a floral promoter. This reduced the concentration of trehalose-6-phosphate (T6P), a sugar signal that regulates growth and development, and increased the concentration of sucrose in ear spikelets. Overexpression of TPP increased both kernel set and harvest index. Field data at several sites and over multiple seasons showed that the engineered trait improved yields from 9% to 49% under non-drought or mild drought conditions, and from 31% to 123% under more severe drought conditions, relative to yields from nontransgenic controls.

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Evidence That the Origin of Naked Kernels During Maize Domestication Was Caused by a Single Amino Acid Substitution in tga1

teosinte glume architecture1 (tga1), a member of the SBP-box gene family of transcriptional regulators, has been identified as the gene conferring naked kernels in maize vs. encased kernels in its wild progenitor, teosinte. However, the identity of the causative polymorphism within tga1 that produces these different phenotypes has remained unknown. Using nucleotide diversity data, we show that there is a single fixed nucleotide difference between maize and teosinte in tga1, and this difference confers a Lys (teosinte allele) to Asn (maize allele) substitution. This substitution transforms TGA1 into a transcriptional repressor. While both alleles of TGA1 can bind a GTAC motif, maize-TGA1 forms more stable dimers than teosinte-TGA1. Since it is the only fixed difference between maize and teosinte, this alteration in protein function likely underlies the differences in maize and teosinte glume architecture. We previously reported a difference in TGA1 protein abundance between maize and teosinte based on relative signal intensity of a Western blot. Here, we show that this signal difference is not due to tga1 but to a second gene, neighbor of tga1 (not1). Not1encodes a protein that has 92% amino acid similarity to TGA1 and that is recognized by the TGA1 antibody. Genetic mapping and phenotypic data show that tga1, without a contribution from not1, controls the difference in covered vs. naked kernels. No trait differences could be associated with the maize vs. teosinte alleles of not1. Our results document how morphological evolution can be driven by a simple nucleotide change that alters protein function.

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Self-DNA: a blessing in disguise?

Self-DNA: a blessing in disguise? | Emerging Research in Plant Cell Biology | Scoop.it

Mazzoleni et al. (2015a,b) in two recent papers provided novel and rigorous evidence for a unique detrimental effect of self-DNA (i.e. DNA originating from conspecifics) on organismal growth. The authors investigated the effect as a means of explaining plant–soil feedbacks via plant litter (Mazzoleni et al., 2015a) and subsequently convincingly generalized their observations to a range of additional organisms including protozoa, algae, fungi and animals. The authors explain the growth suppression on the basis of inhibitory effects of self-DNA. They argue that this inhibition mechanism, through facilitating coexistence, represents a mechanism of maintaining diversity. The ecological, physiological and molecular significance of the observations of Mazzoleni et al. (2015a,b) is thought-provoking. A priority now is to start a discourse on the interpretation of the results of these studies, because this will help design focused experiments to further investigate the role of self-DNA on growth.

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The butterfly plant arms-race escalated by gene and genome duplications

The butterfly plant arms-race escalated by gene and genome duplications | Emerging Research in Plant Cell Biology | Scoop.it

Coevolutionary interactions are thought to have spurred the evolution of key innovations and driven the diversification of much of life on Earth. However, the genetic and evolutionary basis of the innovations that facilitate such interactions remains poorly understood. We examined the coevolutionary interactions between plants (Brassicales) and butterflies (Pieridae), and uncovered evidence for an escalating evolutionary arms-race. Although gradual changes in trait complexity appear to have been facilitated by allelic turnover, key innovations are associated with gene and genome duplications. Furthermore, we show that the origins of both chemical defenses and of molecular counter adaptations were associated with shifts in diversification rates during the arms-race. These findings provide an important connection between the origins of biodiversity, coevolution, and the role of gene and genome duplications as a substrate for novel traits.

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Chitin-mediated plant–fungal interactions: catching, hiding and handshaking

Chitin-mediated plant–fungal interactions: catching, hiding and handshaking | Emerging Research in Plant Cell Biology | Scoop.it

Highlights•

Plants recognize infecting fungi through the perception of released chitin fragments by LysM receptor complexes.

Pathogenic fungi secrete effectors and change their cell walls to escape from the chitin-mediated immune system.

Chitin-related molecules also serve as symbiotic signals in rhizobium/AM symbiosis.

Dual function of OsCERK1 in both chitin-mediated immunity and AM symbiosis sheds a new light on the evolutionary relationships between these systems.

Plants can detect infecting fungi through the perception of chitin oligosaccharides by lysin motif receptors such as CEBiP and CERK1. A major function of CERK1 seems to be as a signaling molecule in the receptor complex formed with ligand-binding molecules and to activate downstream defense signaling. Fungal pathogens, however, have developed counter strategies to escape from the chitin-mediated detection by using effectors and/or changing their cell walls. Common structural features between chitin and Nod-/Myc-factors and corresponding receptors have suggested the close relationships between the chitin-mediated immunity and rhizobial/arbuscular mycorrhizal symbiosis. The recent discovery of the dual function of OsCERK1 in both plant immunity and mycorrhizal symbiosis sheds new light on the evolutionary relationships between defense and symbiotic systems in plants.

Current Opinion in Plant Biology 2015, 26:xx–


Via Christophe Jacquet
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Small RNAs—the secret agents in the plant–pathogen interactions

Small RNAs—the secret agents in the plant–pathogen interactions | Emerging Research in Plant Cell Biology | Scoop.it

Highlights•

Small RNAs regulate plant immune responses and pathogen virulence.

Small RNAs can move between interacting organisms and induce cross-kingdom RNAi.

Advanced plant pathogens use cross-kingdom RNAi to suppress host immunity genes.

Host induced gene silencing provides a mechanism whereby crops produce small RNAs to silence pathogen genes

Eukaryotic regulatory small RNAs (sRNAs) that induce RNA interference (RNAi) are involved in a plethora of biological processes, including host immunity and pathogen virulence. In plants, diverse classes of sRNAs contribute to the regulation of host innate immunity. These immune-regulatory sRNAs operate through distinct RNAi pathways that trigger transcriptional or post-transcriptional gene silencing. Similarly, many pathogen-derived sRNAs also regulate pathogen virulence. Remarkably, the influence of regulatory sRNAs is not limited to the individual organism in which they are generated. It can sometimes extend to interacting species from even different kingdoms. There they trigger gene silencing in the interacting organism, a phenomenon called cross-kingdom RNAi. This is exhibited in advanced pathogens and parasites that produce sRNAs to suppress host immunity. Conversely, in host-induced gene silencing (HIGS), diverse plants are engineered to trigger RNAi against pathogens and pests to confer host resistance. Cross-kingdom RNAi opens up a vastly unexplored area of research on mobile sRNAs in the battlefield between hosts and pathogens.


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Chloroplast Stromules Function during Innate Immunity: Developmental Cell

Chloroplast Stromules Function during Innate Immunity: Developmental Cell | Emerging Research in Plant Cell Biology | Scoop.it
•Chloroplast stromules are induced during plant immune responses•Pro-PCD signals such as SA and H2O2 induce stromules•Stromules form dynamic connections with nucleus during immune responses•Constitutively induced stromules enhance PCD during plant immune responses

 

Summary

Inter-organellar communication is vital for successful innate immune responses that confer defense against pathogens. However, little is known about how chloroplasts, which are a major production site of pro-defense molecules, communicate and coordinate with other organelles during defense. Here we show that chloroplasts send out dynamic tubular extensions called stromules during innate immunity or exogenous application of the pro-defense signals, hydrogen peroxide (H2O2) and salicylic acid. Interestingly, numerous stromules surround nuclei during defense response, and these connections correlate with an accumulation of chloroplast-localized NRIP1 defense protein and H2O2 in the nucleus. Furthermore, silencing and knockout ofchloroplast unusual positioning 1 (CHUP1) that encodes a chloroplast outer envelope protein constitutively induces stromules in the absence of pathogen infection and enhances programmed cell death. These results support a model in which stromules aid in the amplification and/or transport of pro-defense signals into the nucleus and other subcellular compartments during immunity.

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Genomics as the key to unlocking the polyploid potential of wheat

Genomics as the key to unlocking the polyploid potential of wheat | Emerging Research in Plant Cell Biology | Scoop.it

Polyploidy has played a central role in plant genome evolution and in the formation of new species such as tetraploid pasta wheat and hexaploid bread wheat. Until recently, the high sequence conservation between homoeologous genes, together with the large genome size of polyploid wheat, had hindered genomic analyses in this important crop species. In the past 5 yr, however, the advent of next-generation sequencing has radically changed the wheat genomics landscape. Here, we review a series of advances in genomic resources and tools for functional genomics that are shifting the paradigm of what is possible in wheat molecular genetics and breeding. We discuss how understanding the relationship between homoeologues can inform approaches to modulate the response of quantitative traits in polyploid wheat; we also argue that functional redundancy has ‘locked up’ a wide range of phenotypic variation in wheat. We explore how genomics provides key tools to inform targeted manipulation of multiple homoeologues, thereby allowing researchers and plant breeders to unlock the full polyploid potential of wheat.

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Genome Sequencing of Arabidopsis abp1-5 Reveals Second-Site Mutations That May Affect Phenotypes

Genome Sequencing of Arabidopsis abp1-5 Reveals Second-Site Mutations That May Affect Phenotypes | Emerging Research in Plant Cell Biology | Scoop.it

Another chink in the ABP armor - ABP1 was identified back in the 1970s as an Auxin Binding Protein. Evidence for its functional role came from knock-down studies using antisense RNA, intereferring with its function by the addition of monoclonal antibodies, and finally the identification of Arabidopsis mutants, which were difficult to study as they conferred an embryo-lethal phenotype. Subsequently, a weaker allele was identified, abp1-5, with a phenotype consistent with a role for ABP in auxin signaling.

Earlier this year, Gao et al got our attention by generating mutations in the ABP gene using genome-editing CRISPR technology; the advantage of this approach is it doesn't subject the genome to other off-site mutations. Gao et al stated, "Auxin binding protein 1 (ABP1) is not required for either auxin signaling or Arabidopsis development", which raised questions about the origin of the phenotypes described previously (http://www.pnas.org/content/112/7/2275.abstract).

Now a new study suggests that the phenotype of abp1-5 could come at least in part from those other, messy mutations. By sequencing the whole genome of abp1-5 (an approach that was not readily available until recently), Enders et al found "Genome Sequencing of Arabidopsis abp1-5 Reveals Second-Site Mutations That May Affect Phenotypes" (http://www.plantcell.org/content/early/2015/06/23/tpc.15.00214.abstract).

There are still unanswered questions, but this new study is an important contribution to the question of ABP1 function, and a good paper with which to show that the path to knowledge is not always obstacle free.


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New Phytologist - Volume 207, Issue 2 - Evolutionary plant radiations - Wiley Online Library

New Phytologist - Volume 207, Issue 2 - Evolutionary plant radiations - Wiley Online Library | Emerging Research in Plant Cell Biology | Scoop.it
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Multilayered Organization of Jasmonate Signalling in the Regulation of Root Growth

Multilayered Organization of Jasmonate Signalling in the Regulation of Root Growth | Emerging Research in Plant Cell Biology | Scoop.it
Author Summary The study of plant development is generally carried out in the absence of physical injury. However, damage to plant organs through biotic and abiotic insult is common in nature. Under these conditions the jasmonate pathway that has a low activity in unstressed vegetative tissues imposes its activity on cell division and elongation. Such jasmonate-dependent growth restriction can strongly impact plant productivity. Taking roots as a model, we show that it is possible to manipulate regulatory layers in jasmonate signalling such that cell division and cell elongation can be constrained differently. This approach may lead to future strategies to alter organ growth. Moreover, during this study we identified a novel mutant in a key regulator of the jasmonate pathway. This mutant generated a positive regulator of jasmonate signalling that was so active that we were able to show that hormone synthesis can be completely uncoupled from hormone responses, suggesting ways to modify traits of potential agronomic importance.
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A fungal monooxygenase-derived jasmonate attenuates host innate immunity

A fungal monooxygenase-derived jasmonate attenuates host innate immunity | Emerging Research in Plant Cell Biology | Scoop.it

Distinct modifications fine-tune the activity of jasmonic acid (JA) in regulating plant growth and immunity. Hydroxylated JA (12OH-JA) promotes flower and tuber development but prevents induction of JA signaling, plant defense or both. However, biosynthesis of 12OH-JA has remained elusive. We report here an antibiotic biosynthesis monooxygenase (Abm) that converts endogenous free JA into 12OH-JA in the model rice blast fungus Magnaporthe oryzae. Such fungal 12OH-JA is secreted during host penetration and helps evade the defense response. Loss of Abm in M. oryzae led to accumulation of methyl JA (MeJA), which induces host defense and blocks invasive growth. Exogenously added 12OH-JA markedly attenuated abmΔ-induced immunity in rice. Notably, Abm itself is secreted after invasion and most likely converts plant JA into 12OH-JA to facilitate host colonization. This study sheds light on the chemical arms race during plant-pathogen interaction, reveals Abm as an antifungal target and outlines a synthetic strategy for transformation of a versatile small-molecule phytohormone.

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Rethinking how volatiles are released from plant cells

For plant volatile organic compounds (VOCs) to be emitted, they must cross membrane(s), the aqueous cell wall, and sometimes the cuticle, before moving into the gas phase. It is presumed that VOC movement through each barrier occurs via passive diffusion. However, VOCs, which are primarily nonpolar compounds, will preferentially partition into membranes, making diffusion into aqueous compartments slow. Using Fick's first law, we calculated that to achieve observed VOC emission rates by diffusion alone would necessitate toxic VOC levels in membranes. Here, we propose that biological mechanisms, such as those involved in trafficking other hydrophobic compounds, must contribute to VOC emission. Such parallel biological pathways would lower barrier resistances and, thus, steady-state emission rates could be maintained with significantly reduced intramembrane VOC concentrations.

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Expression of barley SUSIBA2 transcription factor yields high-starch low-methane rice

Expression of barley SUSIBA2 transcription factor yields high-starch low-methane rice | Emerging Research in Plant Cell Biology | Scoop.it

Atmospheric methane is the second most important greenhouse gas after carbon dioxide, and is responsible for about 20% of the global warming effect since pre-industrial times1, 2. Rice paddies are the largest anthropogenic methane source and produce 7–17% of atmospheric methane2, 3. Warm waterlogged soil and exuded nutrients from rice roots provide ideal conditions for methanogenesis in paddies with annual methane emissions of 25–100-million tonnes3, 4. This scenario will be exacerbated by an expansion in rice cultivation needed to meet the escalating demand for food in the coming decades4. There is an urgent need to establish sustainable technologies for increasing rice production while reducing methane fluxes from rice paddies. However, ongoing efforts for methane mitigation in rice paddies are mainly based on farming practices and measures that are difficult to implement5. Despite proposed strategies to increase rice productivity and reduce methane emissions4, 6, no high-starch low-methane-emission rice has been developed. Here we show that the addition of a single transcription factor gene, barleySUSIBA2 (refs 7, 8), conferred a shift of carbon flux to SUSIBA2 rice, favouring the allocation of photosynthates to aboveground biomass over allocation to roots. The altered allocation resulted in an increased biomass and starch content in the seeds and stems, and suppressed methanogenesis, possibly through a reduction in root exudates. Three-year field trials in China demonstrated that the cultivation of SUSIBA2 rice was associated with a significant reduction in methane emissions and a decrease in rhizospheric methanogen levels. SUSIBA2 rice offers a sustainable means of providing increased starch content for food production while reducing greenhouse gas emissions from rice cultivation. Approaches to increase rice productivity and reduce methane emissions as seen in SUSIBA2 rice may be particularly beneficial in a future climate with rising temperatures resulting in increased methane emissions from paddies9, 10.

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Genetic Determinants of the Network of Primary Metabolism and Their Relationships to Plant Performance in a Maize Recombinant Inbred Line Population

Genetic Determinants of the Network of Primary Metabolism and Their Relationships to Plant Performance in a Maize Recombinant Inbred Line Population | Emerging Research in Plant Cell Biology | Scoop.it

Deciphering the influence of genetics on primary metabolism in plants will provide insights useful for genetic improvement and enhance our fundamental understanding of plant growth and development. Although maize (Zea mays) is a major crop for food and feed worldwide, the genetic architecture of its primary metabolism is largely unknown. Here, we use high-density linkage mapping to dissect large-scale metabolic traits measured in three different tissues (leaf at seedling stage, leaf at reproductive stage, and kernel at 15 d after pollination [DAP]) of a maize recombinant inbred line population. We identify 297 quantitative trait loci (QTLs) with moderate (86.2% of the mapped QTL, R2 = 2.4 to 15%) to major effects (13.8% of the mapped QTL, R2 >15%) for 79 primary metabolites across three tissues. Pairwise epistatic interactions between these identified loci are detected for more than 25.9% metabolites explaining 6.6% of the phenotypic variance on average (ranging between 1.7 and 16.6%), which implies that epistasis may play an important role for some metabolites. Key candidate genes are highlighted and mapped to carbohydrate metabolism, the tricarboxylic acid cycle, and several important amino acid biosynthetic and catabolic pathways, with two of them being further validated using candidate gene association and expression profiling analysis. Our results reveal a metabolite-metabolite-agronomic trait network that, together with the genetic determinants of maize primary metabolism identified herein, promotes efficient utilization of metabolites in maize improvement.

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A roadmap for research on crassulacean acid metabolism (CAM) to enhance sustainable food and bioenergy production in a hotter, drier world .

A roadmap for research on crassulacean acid metabolism (CAM) to enhance sustainable food and bioenergy production in a hotter, drier world . | Emerging Research in Plant Cell Biology | Scoop.it

Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that features nocturnal CO2 uptake, facilitates increased water-use efficiency (WUE), and enables CAM plants to inhabit water-limited environments such as semi-arid deserts or seasonally dry forests. Human population growth and global climate change now present challenges for agricultural production systems to increase food, feed, forage, fiber, and fuel production. One approach to meet these challenges is to increase reliance on CAM crops, such as Agave andOpuntia, for biomass production on semi-arid, abandoned, marginal, or degraded agricultural lands. Major research efforts are now underway to assess the productivity of CAM crop species and to harness the WUE of CAM by engineering this pathway into existing food, feed, and bioenergy crops. An improved understanding of CAM has potential for high returns on research investment. To exploit the potential of CAM crops and CAM bioengineering, it will be necessary to elucidate the evolution, genomic features, and regulatory mechanisms of CAM. Field trials and predictive models will be required to assess the productivity of CAM crops, while new synthetic biology approaches need to be developed for CAM engineering. Infrastructure will be needed for CAM model systems, field trials, mutant collections, and data management.

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Dietary delivery: a new avenue for microRNA therapeutics?: Trends in Biotechnology

Many people carefully monitor their food choices, adhering to the philosophy that ‘you are what you eat’. Recent research adds a new wrinkle to that old adage, suggesting that dietary small RNAs (sRNAs) can control the gene expression of the consumer and may provide an effective, noninvasive, and inexpensive therapy for many human diseases.
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Cues from chewing insects — the intersection of DAMPs, HAMPs, MAMPs and effectors

Cues from chewing insects — the intersection of DAMPs, HAMPs, MAMPs and effectors | Emerging Research in Plant Cell Biology | Scoop.it

Highlights•

Upon feeding, herbivores secrete saliva, regurgitant and frass that come in contact with the plant.

Herbivore's gut symbionts can also be released during feeding and recognized by the plant.

The composition of these secretions and gut microbial community is dependent upon their host plant and the herbivore.

Cues present in herbivore secretions are recognized by plants to trigger defense responses.

Some of these cues can act as effectors or elicitors in a context dependent manner.

Chewing herbivores cause massive damage when crushing plant tissues with their mandibles, thus releasing a vast array of cues that may be perceived by the plant to mobilize defenses. Besides releasing damage cues in wounded tissues, herbivores deposit abundant cues from their saliva, regurgitant and feces that trigger herbivore specific responses in plants. Herbivores can manipulate the perception mechanisms and defense signals to suppress plant defenses by secreting effectors and/or by exploiting their associated oral microbes. Recent studies indicate that both the composition of herbivore cues and the plant's ability to recognize them are highly dependent upon the specific plant–herbivore system. There is a growing amount of work on identifying herbivore elicitors and effectors, but the most significant bottleneck in the discipline is the identification and characterization of plant receptors that perceive these herbivore-specific cues.

 

 


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A Recently Evolved Alternative Splice Site in the BRANCHED1a Gene Controls Potato Plant Architecture: Current Biology

A Recently Evolved Alternative Splice Site in the BRANCHED1a Gene Controls Potato Plant Architecture: Current Biology | Emerging Research in Plant Cell Biology | Scoop.it
•In the Solanum clade, an alternative splice site evolved in the BRC1a gene•Alternative splicing of potato BRC1a renders two proteins with antagonistic functions•BRC1aLong isoform is a transcription factor that prevents shoot and stolon branching•BRC1aShort isoform interacts with and limits BRC1aLong nuclear targeting

 

Summary

Amplification and diversification of transcriptional regulators that control development is a driving force of morphological evolution. A major source of protein diversity is alternative splicing, which leads to the generation of different isoforms from a single gene. The mechanisms and timing of intron evolution nonetheless remain unclear, and the functions of alternative splicing-generated protein isoforms are rarely studied. In Solanum tuberosum, the BRANCHED1a (BRC1a) gene encodes a TCP transcription factor that controls lateral shoot outgrowth. Here, we report the recent evolution in Solanum of an alternative splice site in BRC1a that leads to the generation of two BRC1a protein isoforms with distinct C-terminal regions, BRC1aLong and BRC1aShort, encoded by unspliced and spliced mRNA, respectively. The BRC1aLong C-terminal region has a strong activation domain, whereas that of BRC1aS lacks an activation domain and is predicted to form an amphipathic helix, the H domain, which prevents protein nuclear targeting. BRC1aShort is thus mainly cytoplasmic, while BRC1aLong is mainly nuclear. BRC1aLong functions as a transcriptional activator, whereas BRC1aShort appears to have no transcriptional activity. Moreover, BRC1aShort can heterodimerize with BRC1aLong and act as a dominant-negative factor; it increases BRC1aLong concentration in cytoplasm and reduces its transcriptional activity. This alternative splicing mechanism is regulated by hormones and external stimuli that control branching. The evolution of a new alternative splicing site and a novel protein domain in Solanum BRC1a led to a multi-level mechanism of post-transcriptional and post-translational BRC1a regulation that effectively modulates its branch suppressing activity in response to environmental and endogenous cues.

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The first crop plant genetically engineered to release an insect pheromone for defence

The first crop plant genetically engineered to release an insect pheromone for defence | Emerging Research in Plant Cell Biology | Scoop.it

Insect pheromones offer potential for managing pests of crop plants. Volatility and instability are problems for deployment in agriculture but could be solved by expressing genes for the biosynthesis of pheromones in the crop plants. This has now been achieved by genetically engineering a hexaploid variety of wheat to release (E)-β-farnesene (Eβf), the alarm pheromone for many pest aphids, using a synthetic gene based on a sequence from peppermint with a plastid targeting amino acid sequence, with or without a gene for biosynthesis of the precursor farnesyl diphosphate. Pure Eβf was produced in stably transformed wheat lines with no other detectable phenotype but requiring targeting of the gene produced to the plastid. In laboratory behavioural assays, three species of cereal aphids were repelled and foraging was increased for a parasitic natural enemy. Although these studies show considerable potential for aphid control, field trials employing the single and double constructs showed no reduction in aphids or increase in parasitism. Insect numbers were low and climatic conditions erratic suggesting the need for further trials or a closer imitation, in the plant, of alarm pheromone release.

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PNAS: The butterfly plant arms-race escalated by gene and genome duplications (2015)

PNAS: The butterfly plant arms-race escalated by gene and genome duplications (2015) | Emerging Research in Plant Cell Biology | Scoop.it

Coevolutionary interactions are thought to have spurred the evolution of key innovations and driven the diversification of much of life on Earth. However, the genetic and evolutionary basis of the innovations that facilitate such interactions remains poorly understood. We examined the coevolutionary interactions between plants (Brassicales) and butterflies (Pieridae), and uncovered evidence for an escalating evolutionary arms-race. Although gradual changes in trait complexity appear to have been facilitated by allelic turnover, key innovations are associated with gene and genome duplications. Furthermore, we show that the origins of both chemical defenses and of molecular counter adaptations were associated with shifts in diversification rates during the arms-race. These findings provide an important connection between the origins of biodiversity, coevolution, and the role of gene and genome duplications as a substrate for novel traits.


See also blog post https://decodingscience.missouri.edu/2015/06/22/scientists-uncover-how-caterpillars-created-condiments/


Via Kamoun Lab @ TSL, Mary Williams
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Marcelo Errera's curator insight, July 30, 9:23 AM

That's an interesting study. How diversity was (and still is) built over time is one of the greatest challenge in evolutionary biology.

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Repression of microRNA biogenesis by silencing of OsDCL1 activates the basal resistance to Magnaporthe oryzae in rice

Repression of microRNA biogenesis by silencing of OsDCL1 activates the basal resistance to Magnaporthe oryzae in rice | Emerging Research in Plant Cell Biology | Scoop.it
Highlights



OsDCL1 RNAi lines showed enhanced resistance to rice blast.


A negative feedback loop between miR162a and OsDCL1 was identified.


Differentially expressed miRNAs responsive to rice blast infection were identified.


PR and PTI responsive genes were constitutively activated in OsDCL1 RNAi lines.

Abstract

The RNaseIII enzyme Dicer-like 1 (DCL1) processes the microRNA biogenesis and plays a determinant role in plant development. In this study, we reported the function of OsDCL1 in the immunity to rice blast, the devastating disease caused by the fungal pathogen, Magnaporthe oryzae. Expression profiling demonstrated that different OsDCLs responded dynamically and OsDCL1 reduced its expression upon the challenge of rice blast pathogen. In contrast, miR162a predicted to target OsDCL1 increased its expression, implying a negative feedback loop between OsDCL1 and miR162a in rice. In addition to developmental defects, the OsDCL1-silencing mutants showed enhanced resistance to virulent rice blast strains in a non-race specific manner. Accumulation of hydrogen peroxide and cell death were observed in the contact cells with infectious hyphae, revealing that silencing of OsDCL1 activated cellular defense responses. In OsDCL1 RNAi lines, 12 differentially expressed miRNAs were identified, of which 5 and 7 were down- and up-regulated, respectively, indicating that miRNAs responded dynamically in the interaction between rice and rice blast. Moreover, silencing of OsDCL1 activated the constitutive expression of defense related genes. Taken together, our results indicate that rice is capable of activating basal resistance against rice blast by perturbing OsDCL1-dependent miRNA biogenesis pathway.

Via Christophe Jacquet
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Rescooped by Jennifer Mach from MycorWeb Plant-Microbe Interactions
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Frontiers | Does plant immunity play a critical role during initiation of the legume-rhizobium symbiosis? | Plant-Microbe Interaction

Frontiers | Does plant immunity play a critical role during initiation of the legume-rhizobium symbiosis? | Plant-Microbe Interaction | Emerging Research in Plant Cell Biology | Scoop.it
Plants are exposed to many different microbes in their habitats. These microbes may be benign or pathogenic, but in some cases they are beneficial for the host. The rhizosphere provides an especially rich palette for colonization by beneficial (associative and symbiotic) microorganisms, which raises the question as to how roots can distinguish such ‘friends’ from possible ‘foes’ (i.e., pathogens). Plants possess an innate immune system that can recognize pathogens, through an arsenal of protein receptors, including receptor-like kinases (RLKs) and receptor-like proteins (RLPs) located at the plasma membrane. In addition, the plant host has intracellular receptors (so called NBS-LRR proteins or R proteins) that directly or indirectly recognize molecules released by microbes into the plant cell. A successful cooperation between legume plants and rhizobia leads to beneficial symbiotic interaction. The key rhizobial, symbiotic signaling molecules [lipo-chitooligosaccharide Nod factors (NF)] are perceived by the host legume plant using lysin motif-domain containing RLKs. Perception of the symbiotic NFs trigger signaling cascades leading to bacterial infection and accommodation of the symbiont in a newly formed root organ, the nodule, resulting in a nitrogen-fixing root nodule symbiosis. The net result of this symbiosis is the intracellular colonization of the plant with thousands of bacteria; a process that seems to occur in spite of the immune ability of plants to prevent pathogen infection. In this review, we discuss the potential of the invading rhizobial symbiont to actively avoid this innate immune response, as well as specific examples of where the plant immune response may modulate rhizobial infection and host range.

Via Francis Martin
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