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NY Times: The Worldwide Vulnerability of Forests (2012)

NY Times: The Worldwide Vulnerability of Forests (2012) | Emerging Research in Plant Cell Biology | Scoop.it

Many trees operate with only a narrow margin of safety when it comes to their water supply, so many of the world's important forest species are vulnerable to hydraulic failure.

 

A warming climate creates summertime water stress for trees like these mountain pines in Montana, making them more vulnerable to attack by beetles. The gray trees above died several years ago.


Via Kamoun Lab @ TSL
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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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The gibberellin precursor GA12 acts as a long-distance growth signal in Arabidopsis

The gibberellin precursor GA12 acts as a long-distance growth signal in Arabidopsis | Emerging Research in Plant Cell Biology | Scoop.it

The gibberellin (GA) phytohormones play important roles in plant growth and development, promoting seed germination, elongation growth and reproductive development1. Over the years, substantial progress has been made in understanding the regulation of GA signalling and metabolism, which ensures appropriate levels of GAs for growth and development2. Moreover, an additional level of regulation may reside in the transport of GAs from production sites to recipient tissues that require GAs for growth. Although there is considerable evidence suggesting the existence of short- and long-distance movement of GAs in plants3,4,5,6,7,8, the nature and the biological properties of this transport are not yet understood. Here, we combine biochemical and conventional micrografting experiments in Arabidopsis thaliana to show that the GA precursor GA12, although biologically inactive by itself, is the major mobile GA signal over long distances. Quantitative analysis of endogenous GAs in xylem and phloem exudates further indicates that GA12moves through the plant vascular system. Finally, we demonstrate that GA12 is functional in recipient tissues, supporting growth via the activation of the GA signalling cascade. Collectively, these results reveal the existence of long-range transport of endogenous GA12 in plants that may have implications for the control of developmental phase transitions and the adaptation to adverse environments.

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Chloroplasts play a central role in plant defence and are targeted by pathogen effectors

Chloroplasts play a central role in plant defence and are targeted by pathogen effectors | Emerging Research in Plant Cell Biology | Scoop.it

Microbe associated molecular pattern (MAMP) receptors in plants recognize MAMPs and activate basal defences; however a complete understanding of the molecular and physiological mechanisms conferring immunity remains elusive. Pathogens suppress active defence in plants through the combined action of effector proteins. Here we show that the chloroplast is a key component of early immune responses. MAMP perception triggers the rapid, large-scale suppression of nuclear encoded chloroplast-targeted genes (NECGs). Virulent Pseudomonas syringae effectors reprogramme NECG expression in Arabidopsis, target the chloroplast and inhibit photosynthetic CO2assimilation through disruption of photosystem II. This activity prevents a chloroplastic reactive oxygen burst. These physiological changes precede bacterial multiplication and coincide with pathogen-induced abscisic acid (ABA) accumulation. MAMP pretreatment protects chloroplasts from effector manipulation, whereas application of ABA or the inhibitor of photosynthetic electron transport, DCMU, abolishes the MAMP-induced chloroplastic reactive oxygen burst, and enhances growth of a P. syringae hrpA mutant that fails to secrete effectors.

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Rescooped by Jennifer Mach from Plant roots and rhizosphere
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Recent developments in arbuscular mycorrhizal signaling

Recent developments in arbuscular mycorrhizal signaling | Emerging Research in Plant Cell Biology | Scoop.it
Highlights



Multiple multifunctional receptor like kinases contribute to AM signaling.


CYCLOPS phosphorylation by CCamK directly connects calcium spiking to transcription.


AM signal transduction is mediated by a network of GRAS transcription factors.


Gibberellic acid modulates AM colonization through DELLA repressors.

Plants can establish root endosymbioses with both arbuscular mycorrhizal fungi and rhizobial bacteria to improve their nutrition. Our understanding of the molecular events underlying the establishment of these symbioses has significantly advanced in the last few years. Here I highlight major recent findings in the field of endosymbiosis signaling. Despite the identification of new signaling components and the definition, or in some cases better re-definition of the molecular functions of previously known players, major questions still remain that need to be addressed. Most notably the mechanisms defining signaling specificities within either symbiosis remain unclear.

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Auxin-Mediated Transcriptional System with a Minimal Set of Components Is Critical for Morphogenesis through the Life Cycle in Marchantia polymorpha

Auxin-Mediated Transcriptional System with a Minimal Set of Components Is Critical for Morphogenesis through the Life Cycle in  Marchantia polymorpha | Emerging Research in Plant Cell Biology | Scoop.it
Blurb The liverwort Marchantia polymorpha has a minimal but required repertoire of components for auxin-mediated transcriptional regulation, which is sufficient for achieving the simple yet multi-dimensional body plan.
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What plant hydraulics can tell us about responses to climate-change droughts

What plant hydraulics can tell us about responses to climate-change droughts | Emerging Research in Plant Cell Biology | Scoop.it

Climate change exposes vegetation to unusual drought, causing declines in productivity and increased mortality. Drought responses are hard to anticipate because canopy transpiration and diffusive conductance (G) respond to drying soil and vapor pressure deficit (D) in complex ways. A growing database of hydraulic traits, combined with a parsimonious theory of tree water transport and its regulation, may improve predictions of at-risk vegetation. The theory uses the physics of flow through soil and xylem to quantify how canopy water supply declines with drought and ceases by hydraulic failure. This transpiration ‘supply function’ is used to predict a water ‘loss function’ by assuming that stomatal regulation exploits transport capacity while avoiding failure. Supply–loss theory incorporates root distribution, hydraulic redistribution, cavitation vulnerability, and cavitation reversal. The theory efficiently defines stomatal responses to D, drying soil, and hydraulic vulnerability. Driving the theory with climate predicts drought-induced loss of plant hydraulic conductance (k), canopy G, carbon assimilation, and productivity. Data lead to the ‘chronic stress hypothesis’ wherein > 60% loss of k increases mortality by multiple mechanisms. Supply–loss theory predicts the climatic conditions that push vegetation over this risk threshold. The theory's simplicity and predictive power encourage testing and application in large-scale modeling.

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Cadmium translocation by contractile roots differs from that in regular, non-contractile roots

Cadmium translocation by contractile roots differs from that in regular, non-contractile roots | Emerging Research in Plant Cell Biology | Scoop.it

Background and Aims Contractile roots are known and studied mainly in connection with the process of shrinkage of their basal parts, which acts to pull the shoot of the plant deeper into the ground. Previous studies have shown that the specific structure of these roots results in more intensive water uptake at the base, which is in contrast to regular root types. The purpose of this study was to find out whether the basal parts of contractile roots are also more active in translocation of cadmium to the shoot.

Methods Plants of the South African ornamental species Tritonia gladiolaris were cultivated in vitro for 2 months, at which point they possessed well-developed contractile roots. They were then transferred to Petri dishes with horizontally separated compartments of agar containing 50 µmol Cd(NO3)2 in the region of the root base or the root apex. Seedlings of 4-d-old maize (Zea mays) plants, which do not possess contractile roots, were also transferred to similar Petri dishes. The concentrations of Cd in the leaves of the plants were compared after 10 d of cultivation. Anatomical analyses of Tritonia roots were performed using appropriately stained freehand cross-sections.

Key Results The process of contraction required specific anatomical adaptation of the root base in Tritonia, with less lignified and less suberized tissues in comparison with the subapical part of the root. These unusual developmental characteristics were accompanied by more intensive translocation of Cd ions from the basal part of contractile roots to the leaves than from the apical–subapical root parts. The opposite effects were seen in the non-contractile roots of maize, with higher uptake and transport by the apical parts of the root and lower uptake and transport by the basal part.

Conclusions The specific characteristics of contractile roots may have a significant impact on the uptake of ions, including toxic metals from the soil surface layers. This may be important for plant nutrition, for example in the uptake of nutrients from upper soil layers, which are richer in humus in otherwise nutrient-poor soils, and also has implications for the uptake of surface-soil pollutants.

Background and Aims Contractile roots are known and studied mainly in connection with the process of shrinkage of their basal parts, which acts to pull the shoot of the plant deeper into the ground.

Via Christophe Jacquet
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Rescooped by Jennifer Mach from Plant Biology Teaching Resources (Higher Education)
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A novel highly differentially expressed gene in wheat endosperm associated with bread quality

A novel highly differentially expressed gene in wheat endosperm associated with bread quality | Emerging Research in Plant Cell Biology | Scoop.it

Good one to read with students. The genetics and the plant biology are both easy to understand and the application is very evident.


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Rescooped by Jennifer Mach from Plant-Microbe Symbioses
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Growing rice in controlled environments

Growing rice in controlled environments | Emerging Research in Plant Cell Biology | Scoop.it
Rice (Oryza sativa) is less frequently used in basic research than Arabidopsis, although rice is a valuable model system for many monocot crops and possesses a high genetic variability in physiologically as well as agriculturally relevant features such as abiotic stress tolerance, nutrient efficiency and flower time control. A reason is the seemingly difficult cultivation of rice outside the rice production area. This review aims to assist newcomers to the field to develop cultivation protocols for their local controlled environment. The main challenges are high light demands, photoperiodicity and low micronutrient efficiency. The nutrient efficiency problem can be overcome by adding micronutrient fertiliser to potting substrates and keeping the soil waterlogged to increase micronutrient availability and mobility. Cultivation of rice on adjusted hydroponic solutions with high iron concentration provides the basis for successful heavy isotope labelling. Many rice cultivars need high light intensities in combination with short-day conditions to complete their life cycle. However, some photoperiod-insensitive cultivars will flower even under relatively low light intensities. In highly photoperiod-sensitive cultivars, like Nipponbare, flowering can be induced by a limited period of short-day treatment in the sensitive period, after which the cultivation can be continued in long-day conditions. The life cycle of many cultivars is completed in 90 to 120 days, its length being thus comparable to Arabidopsis and shorter than in other cereals. In conclusion, with the right cultivation technique, rice is an amiable model species for researchers beyond the rice area too.

Via Jean-Michel Ané
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Rescooped by Jennifer Mach from Plant & Evolution
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Genome-wide dosage-dependent and -independent regulation contributes to gene expression and evolutionary novelty in plant polyploids

Polyploidy provides evolutionary and morphological novelties in many plants and some animals. However, the role of genome dosage and composition in gene expression changes remains poorly understood. Here we generated a series of resynthesized Arabidopsis tetraploids that contain 0-4 copies of Arabidopsis thaliana and Arabidopsis arenosagenomes and investigated ploidy and hybridity effects on gene expression. Allelic expression can be defined as dosage–dependent (expression levels correlate with genome dosages) and otherwise dosage–independent. Here we show contribution of many dosage-dependent genes to cell cycle, photosynthesis, and metabolism, whereas dosage-independent genes are enriched in biotic and abiotic stress responses. Interestingly, dosage-dependent genes tend to be preserved in ancient biochemical pathways present in both plant and non-plant species, whereas many dosage-independent genes belong to plant-specific pathways. This is confirmed by an independent analysis using Arabidopsis phylostratigraphic map. ForA. thaliana loci, the dosage-dependent alleles are void of TEs and tend to correlate with H3K9ac, H3K4me3 and CG methylation, whereas the majority of dosage-independent alleles are enriched with TEs and correspond to H3K27me1, H3K27me3 and CHG (H=A, T, or C) methylation. Furthermore, there is a parent-of-origin effect on nonadditively expressed genes in the reciprocal allotetraploids especially when A. arenosa is used as the paternal parent, leading to metabolic and morphological changes. Thus, ploidy, epigenetic modifications, and cytoplasmic-nuclear interactions shape gene expression diversity in polyploids. Dosage-dependent expression can maintain growth and developmental stability, while dosage-independent expression can facilitate functional divergence between homoeologs (subfunctionalization) and/or gain new functions (neofunctionalization) during polyploid evolution.


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Autophagic Recycling Plays a Central Role in Maize Nitrogen Remobilization

Autophagic Recycling Plays a Central Role in Maize Nitrogen Remobilization | Emerging Research in Plant Cell Biology | Scoop.it

Autophagy is a primary route for nutrient recycling in plants by which superfluous or damaged cytoplasmic material and organelles are encapsulated and delivered to the vacuole for breakdown. Central to autophagy is a conjugation pathway that attaches AUTOPHAGY-RELATED8 (ATG8) to phosphatidylethanolamine, which then coats emerging autophagic membranes and helps with cargo recruitment, vesicle enclosure, and subsequent vesicle docking with the tonoplast. A key component in ATG8 function is ATG12, which promotes lipidation upon its attachment to ATG5. Here, we fully defined the maize (Zea mays) ATG system transcriptionally and characterized it genetically through atg12 mutants that block ATG8 modification.atg12 plants have compromised autophagic transport as determined by localization of a YFP-ATG8 reporter and its vacuolar cleavage during nitrogen or fixed-carbon starvation. Phenotypic analyses showed that atg12 plants are phenotypically normal and fertile when grown under nutrient-rich conditions. However, when nitrogen-starved, seedling growth is severely arrested, and as the plants mature, they show enhanced leaf senescence and stunted ear development. Nitrogen partitioning studies revealed that remobilization is impaired in atg12plants, which significantly decreases seed yield and nitrogen-harvest index. Together, our studies demonstrate that autophagy, while nonessential, becomes critical during nitrogen stress and severely impacts maize productivity under suboptimal field conditions.

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Enhanced Arabidopsis pattern-triggered immunity by overexpression of cysteine-rich receptor-like kinases

Enhanced Arabidopsis pattern-triggered immunity by overexpression of cysteine-rich receptor-like kinases | Emerging Research in Plant Cell Biology | Scoop.it

Upon recognition of microbe-associated molecular patterns (MAMPs) such as the bacterial flagellin (or the derived peptide flg22) by pattern-recognition receptors (PRRs) such as the FLAGELLIN SENSING2 (FLS2), plants activate the pattern-triggered immunity (PTI) response. The L-type lectin receptor kinase-VI.2 (LecRK-VI.2) is a positive regulator of Arabidopsis thaliana PTI. Cysteine-rich receptor-like kinases (CRKs) possess two copies of the C-X8-C-X2-C (DUF26) motif in their extracellular domains and are thought to be involved in plant stress resistance, but data about CRK functions are scarce. Here, we show that Arabidopsis overexpressing the LecRK-VI.2-responsive CRK4, CRK6, and CRK36 demonstrated an enhanced PTI response and were resistant to virulent bacteria Pseudomonas syringae pv. tomato DC3000. Notably, the flg22-triggered oxidative burst was primed in CRK4, CRK6, and CRK36 transgenics and up-regulation of the PTI-responsive gene FLG22-INDUCED RECEPTOR-LIKE 1 (FRK1) was potentiated upon flg22 treatment in CRK4 and CRK6 overexpression lines or constitutively increased by CRK36overexpression. PTI-mediated callose deposition was not affected by overexpression of CRK4 andCRK6, while CRK36 overexpression lines demonstrated constitutive accumulation of callose. In addition, Pst DC3000-mediated stomatal reopening was blocked in CRK4 and CRK36overexpression lines, while overexpression of CRK6 induced constitutive stomatal closure suggesting a strengthening of stomatal immunity. Finally, bimolecular fluorescence complementation and co-immunoprecipitation analyses in Arabidopsis protoplasts suggested that the plasma membrane localized CRK4, CRK6, and CRK36 associate with the PRR FLS2. Association with FLS2 and the observation that overexpression of CRK4, CRK6, and CRK36 boosts specific PTI outputs and resistance to bacteria suggest a role for these CRKs in Arabidopsis innate immunity.

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Autophagic Recycling Plays a Central Role in Maize Nitrogen Remobilization

Autophagic Recycling Plays a Central Role in Maize Nitrogen Remobilization | Emerging Research in Plant Cell Biology | Scoop.it

Autophagy is a primary route for nutrient recycling in plants by which superfluous or damaged cytoplasmic material and organelles are encapsulated and delivered to the vacuole for breakdown. Central to autophagy is a conjugation pathway that attaches AUTOPHAGY-RELATED8 (ATG8) to phosphatidylethanolamine, which then coats emerging autophagic membranes and helps with cargo recruitment, vesicle enclosure, and subsequent vesicle docking with the tonoplast. A key component in ATG8 function is ATG12, which promotes lipidation upon its attachment to ATG5. Here, we fully defined the maize (Zea mays) ATG system transcriptionally and characterized it genetically through atg12 mutants that block ATG8 modification.atg12 plants have compromised autophagic transport as determined by localization of a YFP-ATG8 reporter and its vacuolar cleavage during nitrogen or fixed-carbon starvation. Phenotypic analyses showed that atg12 plants are phenotypically normal and fertile when grown under nutrient-rich conditions. However, when nitrogen-starved, seedling growth is severely arrested, and as the plants mature, they show enhanced leaf senescence and stunted ear development. Nitrogen partitioning studies revealed that remobilization is impaired in atg12plants, which significantly decreases seed yield and nitrogen-harvest index. Together, our studies demonstrate that autophagy, while nonessential, becomes critical during nitrogen stress and severely impacts maize productivity under suboptimal field conditions.

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Rescooped by Jennifer Mach from Plants and Microbes
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Nature Reviews Microbiology: The damage-response framework of microbial pathogenesis (2003)

Nature Reviews Microbiology: The damage-response framework of microbial pathogenesis (2003) | Emerging Research in Plant Cell Biology | Scoop.it

All other curves are derived from this basic curve. The arrow indicates that the position of the curve is variable, and depends on the particular host–microorganism interaction. The y-axis denotes host damage as a function of the host response. In this scheme, host damage can occur throughout the host response, but is magnified at both extremes. The host response is represented by a continuum from 'weak' to 'strong'. 'Weak' and 'strong' are terms that can encompass both quantitative and qualitative characteristics of the host response and are used as the best available terms to denote the spectrum of host response as more precise terms are limiting. Weak responses are those that are insufficient, poor or inappropriate — that is, they are not strong enough to benefit the host. Strong responses are those that are excessive, overly robust or inappropriate — that is, they are too strong and can damage the host. When a threshold amount of damage is reached, the host can become symptomatic and if damage is severe, death can ensue. Green, yellow and purple represent health, disease and severe disease, respectively.


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Transcription and processing of primary microRNAs are coupled by Elongator complex in Arabidopsis

Transcription and processing of primary microRNAs are coupled by Elongator complex in Arabidopsis | Emerging Research in Plant Cell Biology | Scoop.it

MicroRNAs (miRNAs) are a class of small non-coding RNAs that play important regulatory roles in gene expression in plants and animals. The biogenesis of miRNAs involves the transcription of primary miRNAs (pri-miRNAs) by RNA polymerase II (RNAPII) and subsequent processing by Dicer or Dicer-like (DCL) proteins. Here we show that the Elongator complex is involved in miRNA biogenesis in Arabidopsis. Disruption of Elongator reduces RNAPII occupancy at miRNA loci and pri-miRNA transcription. We also show that Elongator interacts with the DCL1-containing Dicing complex and lack of Elongator impairs DCL1 localization in the nuclear Dicing body. Finally, we show that pri-miRNA transcripts as well as DCL1 associate with the chromatin of miRNA genes and the chromatin association of DCL1 is compromised in the absence of Elongator. Our results suggest that Elongator functions in both transcription and processing of pri-miRNAs and probably couples these two processes.

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A genetic relationship between nitrogen use efficiency and seedling root traits in maize as revealed by QTL analysis

A genetic relationship between nitrogen use efficiency and seedling root traits in maize as revealed by QTL analysis | Emerging Research in Plant Cell Biology | Scoop.it
That root system architecture (RSA) has an essential role in nitrogen acquisition is expected in maize, but the genetic relationship between RSA and nitrogen use efficiency (NUE) traits remains to be elucidated. Here, the genetic basis of RSA and NUE traits was investigated in maize using a recombination inbred line population that was derived from two lines contrasted for both traits. Under high-nitrogen and low-nitrogen conditions, 10 NUE- and 9 RSA-related traits were evaluated in four field environments and three hydroponic experiments, respectively. In contrast to nitrogen utilization efficiency (NutE), nitrogen uptake efficiency (NupE) had significant phenotypic correlations with RSA, particularly the traits of seminal roots (r = 0.15–0.31) and crown roots (r = 0.15–0.18). A total of 331 quantitative trait loci (QTLs) were detected, including 184 and 147 QTLs for NUE- and RSA-related traits, respectively. These QTLs were assigned into 64 distinct QTL clusters, and ~70% of QTLs for nitrogen-efficiency (NUE, NupE, and NutE) coincided in clusters with those for RSA. Five important QTLs clusters at the chromosomal regions bin1.04, 2.04, 3.04, 3.05/3.06, and 6.07/6.08 were found in which QTLs for both traits had favourable effects from alleles coming from the large-rooted and high-NupE parent. Introgression of these QTL clusters in the advanced backcross-derived lines conferred mean increases in grain yield of ~14.8% for the line per se and ~15.9% in the testcross. These results reveal a significant genetic relationship between RSA and NUE traits, and uncover the most promising genomic regions for marker-assisted selection of RSA to improve NUE in maize.

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Rescooped by Jennifer Mach from Plant Biology Teaching Resources (Higher Education)
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Vesicles versus Tubes: Is Endoplasmic Reticulum-Golgi Transport in Plants Fundamentally Different from Other Eukaryotes?

Vesicles versus Tubes: Is Endoplasmic Reticulum-Golgi Transport in Plants Fundamentally Different from Other Eukaryotes? | Emerging Research in Plant Cell Biology | Scoop.it

I really like this approach to writing review summary. The question is, how does material move between the ER and Golgi - through vesicles or through tubes? The answer isn't simple, as there are data to support both answers, and other possibilities as well. So, "in this article, four leading plant cell biologists attempted to resolve this issue. Unfortunately, their opinions are so divergent and often opposing that it was not possible to reach a consensus. Thus, we decided to let each tell his or her version individually."

http://www.plantphysiol.org/content/168/2/393.abstract

 


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A Simple Auxin Transcriptional Response System Regulates Multiple Morphogenetic Processes in the Liverwort Marchantia polymorpha

A Simple Auxin Transcriptional Response System Regulates Multiple Morphogenetic Processes in the Liverwort  Marchantia polymorpha | Emerging Research in Plant Cell Biology | Scoop.it
Author Summary In flowering plants it is hypothesized the complexity and the robustness of the auxin transcriptional response could be generated by a large number of paralogs encoding components of this signaling network. Yet, it is not known whether alternative embryophyte body plans can be patterned with a simpler auxin transcriptional machinery. We demonstrate that in the liverwort Marchantia polymorpha , the type rather than the number of components of the auxin transcriptional response pathway are sufficient to pattern a complex three-dimensional gametophyte with multiple tissue and cell types. In M . polymorpha , mutations in components of the auxin signaling pathway cause dramatic pleiotropic effects despite having a single class A activating AUXIN RESPONSE FACTOR ( MpARF1 ). This supports the hypothesis that auxin is context dependent and that it facilitates rather than specifies particular developmental processes. We show that auxin signaling is not necessary for survival but it is required to pattern the transition from two-dimensional to three-dimensional growth. This suggests that the evolution of the auxin transcriptional response was critical for the evolution of developmental complexity in land plants.
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Feasibility of new breeding techniques for organic farming: Trends in Plant Science

•Organic farming suffers from lower productivity than conventional agriculture because the use of pesticides, herbicides, and fertilizers is restricted.•Rewilding furnishes crops with lost properties that their ancestors once had to tolerate adverse environmental conditions.•Rewilding is in accordance with the values of organic breeding and would contribute to closing the yield gap.•New breeding techniques that involve methods of genetic engineering allow for rewilding in a way that the final crop cannot be distinguished from a crop bred by traditional means.

 

Organic farming is based on the concept of working ‘with nature’ instead of against it; however, compared with conventional farming, organic farming reportedly has lower productivity. Ideally, the goal should be to narrow this yield gap. In this review, we specifically discuss the feasibility of new breeding techniques (NBTs) for rewilding, a process involving the reintroduction of properties from the wild relatives of crops, as a method to close the productivity gap. The most efficient methods of rewilding are based on modern biotechnology techniques, which have yet to be embraced by the organic farming movement. Thus, the question arises of whether the adoption of such methods is feasible, not only from a technological perspective, but also from conceptual, socioeconomic, ethical, and regulatory perspectives.

Jennifer Mach's insight:

Re-wilding: it's a thing!

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A cascade of arabinosyltransferases controls shoot meristem size in tomato

A cascade of arabinosyltransferases controls shoot meristem size in tomato | Emerging Research in Plant Cell Biology | Scoop.it

Shoot meristems of plants are composed of stem cells that are continuously replenished through a classical feedback circuit involving the homeobox WUSCHEL (WUS) gene and the CLAVATA(CLV) gene signaling pathway. In CLV signaling, the CLV1 receptor complex is bound by CLV3, a secreted peptide modified with sugars. However, the pathway responsible for modifying CLV3 and its relevance for CLV signaling are unknown. Here we show that tomato inflorescence branching mutants with extra flower and fruit organs due to enlarged meristems are defective in arabinosyltransferase genes. The most extreme mutant is disrupted in a hydroxyproline O-arabinosyltransferase and can be rescued with arabinosylated CLV3. Weaker mutants are defective in arabinosyltransferases that extend arabinose chains, indicating that CLV3 must be fully arabinosylated to maintain meristem size. Finally, we show that a mutation in CLV3increased fruit size during domestication. Our findings uncover a new layer of complexity in the control of plant stem cell proliferation.

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A Developmental Framework for Graft Formation and Vascular Reconnection in Arabidopsis thaliana: Current Biology

Plant grafting is a biologically important phenomenon involving the physical joining of two plants to generate a chimeric organism. It is widely practiced in horticulture and used in science to study the long-distance movement of molecules. Despite its widespread use, the mechanism of graft formation and vascular reconnection is not well understood. Here, we study the dynamics and mechanisms of vascular regeneration in Arabidopsis thaliana during graft formation when the vascular strands are severed and reconnected. We demonstrate a temporal separation between tissue attachment, phloem connection, root growth, and xylem connection. By analyzing cell division patterns and hormone responses at the graft junction, we found that tissues initially show an asymmetry in cell division, cell differentiation, and gene expression and, through contact with the opposing tissue, lose this asymmetry and reform the vascular connection. In addition, we identified genes involved in vascular reconnection at the graft junction and demonstrate that these auxin response genes are required below the graft junction. We propose an inter-tissue communication process that occurs at the graft junction and promotes vascular connection by tissue-specific auxin responses involvingABERRANT LATERAL ROOT FORMATION 4 (ALF4). Our study has implications for phenomena where forming vascular connections are important including graft formation, parasitic plant infection, and wound healing.

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Traffic Lines: New Tools for Genetic Analysis in Arabidopsis thaliana

Genetic analysis requires the ability to identify the genotypes of individuals in a segregating population. This task is straightforward if each genotype has a distinctive phenotype, but is difficult if these genotypes are phenotypically similar or identical. We show that Arabidopsisseeds homozygous or heterozygous for a mutation of interest can be identified in a segregating family by placing the mutation in trans to a chromosome carrying a pair of seed-expressed green and red fluorescent transgenes (a “traffic line”) that flank the mutation. Nonfluorescent seeds in the self-pollinated progeny of such a heterozygous plant are usually homozygous for the mutation, whereas seeds with intermediate green and red fluorescence are typically heterozygous for the mutation. This makes it possible to identify seedlings homozygous for mutations that lack an obvious seedling phenotype, and also facilitates the analysis of lethal or sterile mutations, which must be propagated in heterozygous condition. Traffic lines can also be used to identify progeny that have undergone recombination within a defined region of the genome, facilitating genetic mapping and the production of near-isogenic lines. We produced 488 transgenic lines containing single genome-mapped insertions of NAP:dsRED and NAP:eGFP in Columbia (330 lines) and Landsberg erecta (158 lines) and generated sets of traffic lines that span most regions of the Arabidopsis genome. We demonstrated the utility of these lines for identifying seeds of a specific genotype and for generating near-isogenic lines using mutations of WUSCHEL and SHOOTMERISTEMLESS. This new resource significantly decreases the effort and cost of genotyping segregating families and increases the efficiency of experiments that rely on the ability to detect recombination in a defined chromosomal segment.

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Diversification of histone H2A variants during plant evolution

Among eukaryotes, the four core histones show an extremely high conservation of their structure and form nucleosomes that compact, protect, and regulate access to genetic information. Nevertheless, in multicellular eukaryotes the two families, histone H2A and histone H3, have diversified significantly in key residues. We present a phylogenetic analysis across the green plant lineage that reveals an early diversification of the H2A family in unicellular green algae and remarkable expansions of H2A variants in flowering plants. We define motifs and domains that differentiate plant H2A proteins into distinct variant classes. In non-flowering land plants, we identify a new class of H2A variants and propose their possible role in the emergence of the H2A.W variant class in flowering plants.


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Natural Variation Identifies ICARUS1 , a Universal Gene Required for Cell Proliferation and Growth at High Temperatures in Arabidopsis thaliana

Natural Variation Identifies  ICARUS1 , a Universal Gene Required for Cell Proliferation and Growth at High Temperatures in  Arabidopsis thaliana | Emerging Research in Plant Cell Biology | Scoop.it

Plants are highly sensitive to environmental changes and even small variations in ambient temperature have severe consequences on their growth and development. Temperature affects multiple aspects of plant development, but the processes and mechanisms underlying thermo-sensitive growth responses are mostly unknown. Here we exploit natural variation inArabidopsis thaliana to identify and characterize novel components and processes mediating thermo-sensitive growth responses in plants. Phenotypic screening of wild accessions identified several strains displaying pleiotropic growth defects, at cellular and organism levels, specifically at high ambient temperatures. Positional cloning and characterization of the underlying gene revealed that ICARUS1 (ICA1), which encodes a protein of the tRNAHis guanylyl transferase (Thg1) superfamily, is required for plant growth at high temperatures. Transcriptome and gene marker analyses together with DNA content measurements show that ICA1 loss-of-function results in down regulation of cell cycle associated genes at high temperatures, which is linked with a block in G2/M transition and endoreduplication. In addition, plants with mutations in ICA1show enhanced sensitivity to DNA damage. Characterization of additional strains that carry lesions in ICA1, but display normal growth, shows that alternative splicing is likely to alleviate the deleterious effects of some natural mutations. Furthermore, analyses of worldwide and regional collections of natural accessions indicate that ICA1 loss-of-function has arisen several times independently, and that these occur at high frequency in some local populations. Overall our results suggest that ICA1-mediated-modulation of fundamental processes such as tRNAHismaturation, modify plant growth responses to temperature changes in a quantitative and reversible manner, in natural populations.

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The Plant Journal - Volume 82, Issue 3 - Chlamydomonas

The Plant Journal - Volume 82, Issue 3 - Chlamydomonas | Emerging Research in Plant Cell Biology | Scoop.it

Special issue on Chlamydomonas-- all open access!

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