The Arabidopsis mutant cev1 links cell wall signaling to jasmonate and ethylene responses

Genetic linkage analysis of stable QTLs in Gossypium hirsutum RIL population revealed function of GhCesA4 in fiber development

INTRODUCTION

Upland cotton is an important allotetrapolyploid crop providing natural fibers for textile industry. Under the present high-level breeding and production conditions, further simultaneous improvement of fiber quality and yield is facing unprecedented challenges due to their complex negative correlations.

OBJECTIVES

The study was to adequately identify quantitative trait loci (QTLs) and dissect how they orchestrate the formation of fiber quality and yield.

METHODS

A high-density genetic map (HDGM) based on an intraspecific recombinant inbred line (RIL) population consisting of 231 individuals was used to identify QTLs and QTL clusters of fiber quality and yield traits. The weighted gene correlation network analysis (WGCNA) package in R software was utilized to identify WGCNA network and hub genes related to fiber development. Gene functions were verified via virus-induced gene silencing (VIGS) and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 strategies.

RESULTS

An HDGM consisting of 8045 markers was constructed spanning 4943.01 cM of cotton genome. A total of 295 QTLs were identified based on multi-environmental phenotypes. Among 139 stable QTLs, including 35 newly identified ones, seventy five were of fiber quality and 64 yield traits. A total of 33 QTL clusters harboring 74 QTLs were identified. Eleven candidate hub genes were identified via WGCNA using genes in all stable QTLs and QTL clusters. The relative expression profiles of these hub genes revealed their correlations with fiber development. VIGS and CRISPR/Cas9 edition revealed that the hub gene cellulose synthase 4 (GhCesA4, GH_D07G2262) positively regulate fiber length and fiber strength formation and negatively lint percentage.

CONCLUSION

Multiple analyses demonstrate that the hub genes harbored in the QTLs orchestrate the fiber development. The hub gene GhCesA4 has opposite pleiotropic effects in regulating trait formation of fiber quality and yield. The results facilitate understanding the genetic basis of negative correlation between cotton fiber quality and yield.

Mutation of tomato xyloglucan transglucosylase/hydrolase5 increases fruit firmness and contributes to prolonged shelf life

Fruit ripening in tomato is a highly coordinated developmental process accompanied with fruit softening, which is closely associated with cell wall degradation and remodeling. Xyloglucan endotransglucosylase/hydrolases (XTHs) are known to play an essential role in cell wall xyloglucan metabolism. Tomato XTH5 exhibits xyloglucan endotransglucosylase (XET) activity in vitro, but the understanding of its biological role in fruit ripening remains unclear. In this study, we revealed that SlXTH5 is highly expressed in mature fruits. Knockout mutant plants of SlXTH5 were generated by CRISPR/Cas9 gene editing strategy in tomato cultivar Micro-Tom. The mutant fruits showed accelerated transition from unripe to ripe process and earlier ethylene accumulation compared to wild type fruits. Although the mutation of SlXTH5 did not affect the size, weight and number of fruits, it indeed increased fruit firmness and extended shelf life, which is probably attributed to the increased cell layer and cell wall thickness of pericarp tissue. Pathogen infection experiment showed the enhanced resistance of mutant fruits to Botrytis cinerea. These results revealed the role of SlXTH5 in fruit ripening process, and provide new insight into how cell wall metabolism and remodeling regulate fruit softening and shelf life.

Less is more: CRISPR/Cas9-based mutations in DND1 gene enhance tomato resistance to powdery mildew with low fitness costs

Powdery mildew (PM), triggered by Oidium neolycopersici, represents a significant threat and a major concern for the productivity of tomato plants (Solanum lycopersicum L.). The presence of susceptibility (S) genes in plants facilitates pathogen proliferation and their dysfunction can lead to a recessively inherited broad-spectrum and durable type of resistance. Past studies have demonstrated that disrupting the function of DND1 (Defense No Death 1) increases plant resilience against various pathogens, such as powdery mildew (PM), but this comes at the cost of negatively affecting the overall health and vigor of the plant. To investigate the possibility of minimizing the adverse effects of the dnd1 mutation while boosting disease resistance, a CRISPR-Cas9 construct with four single guide RNAs targeting three exons of SlDND1 (Solyc02g088560.4.1) was designed and introduced into the tomato variety Moneymaker (MM) through Agrobacterium tumefaciens-mediated transformation. Three T1 lines (named E1, E3 and E4) were crossed with MM and then selfed to produce TF2 families. All the TF2 plants in homozygous state dnd1/dnd1, showed reduced PM symptoms compared to the heterozygous (DND1/dnd1) and wild type (DND1/DND1) ones. Two full knock-out (KO) mutant events (E1 and E4) encoding truncated DND1 proteins, exhibited clear dwarfness and auto-necrosis phenotypes, while mutant event E3 harbouring deletions of 3 amino acids, showed normal growth in height with less auto-necrotic spots. Analysis of the 3D structures of both the reference and the mutant proteins revealed significant conformational alterations in the protein derived from E3, potentially impacting its function. A dnd1/dnd1 TF2 line (TV181848-9, E3) underwent whole-genome sequencing using Illumina technology, which confirmed the absence of off-target mutations in selected genomic areas. Additionally, no traces of the Cas9 gene were detected, indicating its elimination through segregation. Our findings confirm the role of DND1 as an S-gene in tomato because impairment of this gene leads to a notable reduction in susceptibility to O. neolycopersici. Moreover, we provide, for the first time, a dnd1 mutant allele (E3) that exhibits fitness advantages in comparison with previously reported dnd1 mutant alleles, indicating a possible way to breed with dnd1 mutants.

Reshaping the Primary Cell Wall: Dual Effects on Plant Resistance to Ralstonia solanacearum and Heat Stress Response

Temperature elevation drastically affects plant defense responses to Ralstonia solanacearum and inhibits the major source of resistance in Arabidopsis thaliana, which is mediated by the receptor pair RRS1-R/RPS4. In this study, we refined a previous genome-wide association (GWA) mapping analysis by using a local score approach and detected the primary cell wall CESA3 gene as a major gene involved in plant response to R. solanacearum at both 27°C and an elevated temperature, 30°C. We functionally validated CESA3 as a susceptibility gene involved in resistance to R. solanacearum at both 27 and 30°C through a reverse genetic approach. We provide evidence that the cesa3mre1 mutant enhances resistance to bacterial disease and that resistance is associated with an alteration of root cell morphology conserved at elevated temperatures. However, even by forcing the entry of the bacterium to bypass the primary cell wall barrier, the cesa3mre1 mutant still showed enhanced resistance to R. solanacearum with delayed onset of bacterial wilt symptoms. We demonstrated that the cesa3mre1 mutant had constitutive expression of the defense-related gene VSP1, which is upregulated at elevated temperatures, and that during infection, its expression level is maintained higher than in the wild-type Col-0. In conclusion, this study reveals that alteration of the primary cell wall by mutating the cellulose synthase subunit CESA3 contributes to enhanced resistance to R. solanacearum, remaining effective under heat stress. We expect that these results will help to identify robust genetic sources of resistance to R. solanacearum in the context of global warming. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Plant triterpenoid saponins function as susceptibility factors to promote the pathogenicity of Botrytis cinerea

The gray mold fungus Botrytis cinerea is a necrotrophic pathogen that causes diseases in hundreds of plant species, including high-value crops. Its polyxenous nature and pathogenic success are due to its ability to perceive host signals in its favor. In this study, we found that laticifer cells of Euphorbia lathyris are a source of susceptibility factors required by B. cinerea to cause disease. Consequently, poor-in-latex (pil) mutants, which lack laticifer cells, show full resistance to this pathogen, whereas lot-of-latex mutants, which produce more laticifer cells, are hypersusceptible. These S factors are triterpenoid saponins, which are widely distributed natural products of vast structural diversity. The downregulation of laticifer-specific oxydosqualene cyclase genes, which encode the first committed step enzymes for triterpene and, therefore, saponin biosynthesis, conferred disease resistance to B. cinerea. Likewise, the Medicago truncatula lha-1 mutant, compromised in triterpenoid saponin biosynthesis, showed enhanced resistance. Interestingly, the application of different purified triterpenoid saponins pharmacologically complemented the disease-resistant phenotype of pil and hla-1 mutants and enhanced disease susceptibility in different plant species. We found that triterpenoid saponins function as plant cues that signal transcriptional reprogramming in B. cinerea, leading to a change in its growth habit and infection strategy, culminating in the abundant formation of infection cushions, the multicellular appressoria apparatus dedicated to plant penetration and biomass destruction in B. cinerea. Taken together, these results provide an explanation for how plant triterpenoid saponins function as disease susceptibility factors to promote B. cinerea pathogenicity.

Roles of the Arabidopsis KEULE Gene in Postembryonic Development

Cytokinesis in plant cells begins with the fusion of vesicles that transport cell wall materials to the center of the cell division plane, where the cell plate forms and expands radially until it fuses with the parental cell wall. Vesicle fusion is facilitated by trans-SNARE complexes, with assistance from Sec1/Munc18 (SM) proteins. The SNARE protein KNOLLE and the SM protein KEULE are required for membrane fusion at the cell plate. Due to the crucial function of KEULE, all Arabidopsis (Arabidopsis thaliana) keule mutants identified to date are seedling lethal. Here, we identified the Arabidopsis serrata4-1 (sea4-1) and sea4-2 mutants, which carry recessive, hypomorphic alleles of KEULE. Homozygous sea4-1 and sea4-2 plants are viable and fertile but have smaller rosettes and fewer leaves at bolting than the wild type. Their leaves are serrated, small, and wavy, with a complex venation pattern. The mutant leaves also develop necrotic patches and undergo premature senescence. RNA-seq revealed transcriptome changes likely leading to reduced cell wall integrity and an increase in the unfolded protein response. These findings shed light on the roles of KEULE in postembryonic development, particularly in the patterning of rosette leaves and leaf margins.

Plant cell wall-mediated disease resistance: Current understanding and future perspectives

Beyond their function as structural barriers, plant cell walls are essential elements for the adaptation of plants to environmental conditions. Cell walls are dynamic structures whose composition and integrity can be altered in response to environmental challenges and developmental cues. These wall changes are perceived by plant sensors/receptors to trigger adaptative responses during development and upon stress perception. Plant cell wall damage caused by pathogen infection, wounding, or other stresses leads to the release of wall molecules, such as carbohydrates (glycans), that function as damage-associated molecular patterns (DAMPs). DAMPs are perceived by the extracellular ectodomains (ECDs) of pattern recognition receptors (PRRs) to activate pattern-triggered immunity (PTI) and disease resistance. Similarly, glycans released from the walls and extracellular layers of microorganisms interacting with plants are recognized as microbe-associated molecular patterns (MAMPs) by specific ECD-PRRs triggering PTI responses. The number of oligosaccharides DAMPs/MAMPs identified that are perceived by plants has increased in recent years. However, the structural mechanisms underlying glycan recognition by plant PRRs remain limited. Currently, this knowledge is mainly focused on receptors of the LysM-PRR family, which are involved in the perception of various molecules, such as chitooligosaccharides from fungi and lipo-chitooligosaccharides (i.e., Nod/MYC factors from bacteria and mycorrhiza, respectively) that trigger differential physiological responses. Nevertheless, additional families of plant PRRs have recently been implicated in oligosaccharide/polysaccharide recognition. These include receptor kinases (RKs) with leucine-rich repeat and Malectin domains in their ECDs (LRR-MAL RKs), Catharanthus roseus RECEPTOR-LIKE KINASE 1-LIKE group (CrRLK1L) with Malectin-like domains in their ECDs, as well as wall-associated kinases, lectin-RKs, and LRR-extensins. The characterization of structural basis of glycans recognition by these new plant receptors will shed light on their similarities with those of mammalians involved in glycan perception. The gained knowledge holds the potential to facilitate the development of sustainable, glycan-based crop protection solutions.

Transcriptome analysis reveals a lncRNA-miRNA-mRNA regulatory network in OsRpp30-mediated disease resistance in rice

BACKGROUND

Long non-coding RNAs (lncRNAs) play critical roles in various biological processes in plants. Extensive studies utilizing high-throughput RNA sequencing have revealed that many lncRNAs are involved in plant disease resistance. Oryza sativa RNase P protein 30 (OsRpp30) has been identified as a positive regulator of rice immunity against fungal and bacterial pathogens. Nevertheless, the specific functions of lncRNAs in relation to OsRpp30-mediated disease resistance in rice remain elusive.

RESULTS

We conducted a comprehensive analysis of lncRNAs, miRNAs, and mRNAs expression patterns in wild type (WT), OsRpp30 overexpression (OsRpp30-OE), and OsRpp30 knockout (OsRpp30-KO) rice plants. In total, we identified 91 differentially expressed lncRNAs (DElncRNAs), 1671 differentially expressed mRNAs (DEmRNAs), and 41 differentially expressed miRNAs (DEmiRNAs) across the different rice lines. To gain further insights, we investigated the interaction between DElncRNAs and DEmRNAs, leading to the discovery of 10 trans- and 27 cis-targeting pairs specific to the OsRpp30-OE and OsRpp30-KO samples. In addition, we constructed a competing endogenous RNA (ceRNA) network comprising differentially expressed lncRNAs, miRNAs, and mRNAs to elucidate their intricate interplay in rice disease resistance. The ceRNA network analysis uncovered a set of gene targets regulated by lncRNAs and miRNAs, which were found to be involved in pathogen recognition, hormone pathways, transcription factor activation, and other biological processes related to plant immunity.

CONCLUSIONS

Our study provides a comprehensive expression profiling of lncRNAs, miRNAs, and mRNAs in a collection of defense mutants in rice. To decipher the putative functional significance of lncRNAs, we constructed trans- and cis-targeting networks involving differentially expressed lncRNAs and mRNAs, as well as a ceRNA network incorporating differentially expressed lncRNAs, miRNAs, and mRNAs. Together, the findings from this study provide compelling evidence supporting the pivotal roles of lncRNAs in OsRpp30-mediated disease resistance in rice.

Cell-type-specific control of secondary cell wall formation by Musashi-type translational regulators in Arabidopsis

Deciphering the mechanism of secondary cell wall/SCW formation in plants is key to understanding their development and the molecular basis of biomass recalcitrance. Although transcriptional regulation is essential for SCW formation, little is known about the implication of post-transcriptional mechanisms in this process. Here we report that two bonafide RNA-binding proteins homologous to the animal translational regulator Musashi, MSIL2 and MSIL4, function redundantly to control SCW formation in Arabidopsis. MSIL2/4 interactomes are similar and enriched in proteins involved in mRNA binding and translational regulation. MSIL2/4 mutations alter SCW formation in the fibers, leading to a reduction in lignin deposition, and an increase of 4-O-glucuronoxylan methylation. In accordance, quantitative proteomics of stems reveal an overaccumulation of glucuronoxylan biosynthetic machinery, including GXM3, in the msil2/4 mutant stem. We showed that MSIL4 immunoprecipitates GXM mRNAs, suggesting a novel aspect of SCW regulation, linking post-transcriptional control to the regulation of SCW biosynthesis genes.

Genome-wide characterization of 2OGD superfamily for mining of susceptibility factors responding to various biotic stresses in Musa spp

Bananas are an important staple food and cash crop, but they are vulnerable to a variety of pests and diseases that substantially reduce yield and quality. Banana diseases are challenging to control and necessitate an integrated strategy, and development of resistant cultivars is one of the effective ways of managing diseases. Lasting disease resistance is the main goal in crop improvement and resistance mediated by a single resistant (R) gene mostly lack durability. However, long-term resistance can be obtained by inactivating susceptibility factors (S), which facilitate pathogen infection and proliferation. Identification and inactivation of susceptibility factors against the major pathogens like Fusarium oxysporum f. sp. cubense (Foc), Pseudocercospora eumusae and Pratylenchus coffeae in banana will be an effective way in developing banana varieties with more durable resistance. Downy mildew resistance 6 (DMR6) and DMR-like oxygenases (DLO1) are one such susceptibility factors and they belong to 2-oxoglutarate Fe(II) dependent oxygenases (2OGD) superfamily. 2OGDs are known to catalyze a plethora of reactions and also confer resistance to different pathogens in various crops, but not much is known about the 2OGD in Musa species. Through a comprehensive genome-wide analysis, 133 and 122 potential 2OGDs were systematically identified and categorized from the A and B genomes of banana, respectively. Real time expression of dmr6 and dlo1 genes showed positive correlation with transcriptome data upon Foc race1 and TR4 infection and examination of expression pattern of Macma4_04_g22670 (Ma04_g20880) and Macma4_02_g13590 (Ma02_g12040) genes revealed their involvement in Foc race1 and TR4 infections, respectively. Further the expression profile of 2OGDs, specifically Macma4_04_g25310 (Ma04_g23390), Macma4_08_g11980 (Ma08_g12090) and Macma4_04_g38910 (Ma04_g36640) shows that they may play a significant role as a susceptibility factor, particularly against P. eumusae and P. coffeae, implying that they can be exploited as a candidate gene for editing in developing resistant cultivars against these diseases. In summary, our findings contribute to a deeper comprehension of the evolutionary and functional aspects of 2OGDs in Musa spp. Furthermore, they highlight the substantial functions of these family constituents in the progression of diseases. These insights hold significance in the context of enhancing the genetic makeup of bananas to attain extended and more durable resistance against pathogens.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01380-y.

A point mutation in the kinase domain of CRK10 leads to xylem vessel collapse and activation of defence responses in Arabidopsis

Cysteine-rich receptor-like kinases (CRKs) are a large family of plasma membrane-bound receptors ubiquitous in higher plants. However, despite their prominence, their biological roles have remained largely elusive so far. In this study we report the characterization of an Arabidopsis mutant named crk10-A397T in which alanine 397 has been replaced by a threonine in the αC helix of the kinase domain of CRK10, known to be a crucial regulatory module in mammalian kinases. The crk10-A397T mutant is a dwarf that displays collapsed xylem vessels in the root and hypocotyl, whereas the vasculature of the inflorescence develops normally. In situ phosphorylation assays with His-tagged wild type and crk10-A397T versions of the CRK10 kinase domain revealed that both alleles are active kinases capable of autophosphorylation, with the newly introduced threonine acting as an additional phosphorylation site in crk10-A397T. Transcriptomic analysis of wild type and crk10-A397T mutant hypocotyls revealed that biotic and abiotic stress-responsive genes are constitutively up-regulated in the mutant, and a root-infection assay with the vascular pathogen Fusarium oxysporum demonstrated that the mutant has enhanced resistance to this pathogen compared with wild type plants. Taken together our results suggest that crk10-A397T is a gain-of-function allele of CRK10, the first such mutant to have been identified for a CRK in Arabidopsis.

VILLIN2 regulates cotton defense against Verticillium dahliae by modulating actin cytoskeleton remodeling

The active structural change of actin cytoskeleton is a general host response upon pathogen attack. This study characterized the function of the cotton (Gossypium hirsutum) actin-binding protein VILLIN2 (GhVLN2) in host defense against the soilborne fungus Verticillium dahliae. Biochemical analysis demonstrated that GhVLN2 possessed actin-binding, -bundling, and -severing activities. A low concentration of GhVLN2 could shift its activity from actin bundling to actin severing in the presence of Ca2+. Knockdown of GhVLN2 expression by virus-induced gene silencing reduced the extent of actin filament bundling and interfered with the growth of cotton plants, resulting in the formation of twisted organs and brittle stems with a decreased cellulose content of the cell wall. Upon V. dahliae infection, the expression of GhVLN2 was downregulated in root cells, and silencing of GhVLN2 enhanced the disease tolerance of cotton plants. The actin bundles were less abundant in root cells of GhVLN2-silenced plants than in control plants. However, upon infection by V. dahliae, the number of actin filaments and bundles in the cells of GhVLN2-silenced plants was raised to a comparable level as those in control plants, with the dynamic remodeling of the actin cytoskeleton appearing several hours in advance. GhVLN2-silenced plants exhibited a higher incidence of actin filament cleavage in the presence of Ca2+, suggesting that pathogen-responsive downregulation of GhVLN2 could activate its actin-severing activity. These data indicate that the regulated expression and functional shift of GhVLN2 contribute to modulating the dynamic remodeling of the actin cytoskeleton in host immune responses against V. dahliae.

Signals and Their Perception for Remodelling, Adjustment and Repair of the Plant Cell Wall

The integrity of the cell wall is important for plant cells. Mechanical or chemical distortions, tension, pH changes in the apoplast, disturbance of the ion homeostasis, leakage of cell compounds into the apoplastic space or breakdown of cell wall polysaccharides activate cellular responses which often occur via plasma membrane-localized receptors. Breakdown products of the cell wall polysaccharides function as damage-associated molecular patterns and derive from cellulose (cello-oligomers), hemicelluloses (mainly xyloglucans and mixed-linkage glucans as well as glucuronoarabinoglucans in Poaceae) and pectins (oligogalacturonides). In addition, several types of channels participate in mechanosensing and convert physical into chemical signals. To establish a proper response, the cell has to integrate information about apoplastic alterations and disturbance of its wall with cell-internal programs which require modifications in the wall architecture due to growth, differentiation or cell division. We summarize recent progress in pattern recognition receptors for plant-derived oligosaccharides, with a focus on malectin domain-containing receptor kinases and their crosstalk with other perception systems and intracellular signaling events.

Memory or acclimation of water stress in pea rely on root system's plasticity and plant's ionome modulation

INTRODUCTION

Peas, as legume crops, could play a major role in the future of food security in the context of worldwide human nutrient deficiencies coupled with the growing need to reduce consumption of animal products. However, pea yields, in terms of quantity and quality (i.e. grain content), are both susceptible to climate change, and more specifically to water deficits, which nowadays occur more frequently during crop growth cycles and tend to last longer. The impact of soil water stress on plant development and plant growth is complex, as its impact varies depending on soil water availability (through the modulation of elements available in the soil), and by the plant's ability to acclimate to continuous stress or to memorize previous stress events.

METHOD

To identify the strategies underlying these plant responses to water stress events, pea plants were grown in controlled conditions under optimal water treatment and different types of water stress; transient (during vegetative or reproductive periods), recurrent, and continuous (throughout the plant growth cycle). Traits related to water, carbon, and ionome uptake and uses were measured and allowed the identification typical plant strategies to cope with water stress.

CONCLUSION

Our results highlighted (i) the common responses to the three types of water stress in shoots, involving manganese (Mn) in particular, (ii) the potential implications of boron (B) for root architecture modification under continuous stress, and (iii) the establishment of an "ecophysiological imprint" in the root system via an increase in nodule numbers during the recovery period.

Plant Cell Wall Integrity Perturbations and Priming for Defense

A plant cell wall is a highly complex structure consisting of networks of polysaccharides, proteins, and polyphenols that dynamically change during growth and development in various tissues. The cell wall not only acts as a physical barrier but also dynamically responds to disturbances caused by biotic and abiotic stresses. Plants have well-established surveillance mechanisms to detect any cell wall perturbations. Specific immune signaling pathways are triggered to contrast biotic or abiotic forces, including cascades dedicated to reinforcing the cell wall structure. This review summarizes the recent developments in molecular mechanisms underlying maintenance of cell wall integrity in plant-pathogen and parasitic interactions. Subjects such as the effect of altered expression of endogenous plant cell-wall-related genes or apoplastic expression of microbial cell-wall-modifying enzymes on cell wall integrity are covered. Targeted genetic modifications as a tool to study the potential of cell wall elicitors, priming of signaling pathways, and the outcome of disease resistance phenotypes are also discussed. The prime importance of understanding the intricate details and complete picture of plant immunity emerges, ultimately to engineer new strategies to improve crop productivity and sustainability.

The function of the plant cell wall in plant-microbe interactions

The plant cell wall is an interface of plant-microbe interactions. The ability of microbes to decompose cell wall polysaccharides contributes to microbial pathogenicity. Plants have evolved mechanisms to prevent cell wall degradation. However, the role of the cell wall in plant-microbe interactions is not well understood. Here, we discuss four functions of the plant cell wall-physical defence, storage of antimicrobial compounds, production of cell wall-derived elicitors, and provision of carbon sources-in the context of plant-microbe interactions. In addition, we discuss the four families of cell surface receptors associated with plant cell walls (malectin-like receptor kinase family, wall-associated kinase family, leucine-rich repeat receptor-like kinase family, and lysin motif receptor-like kinase family) that have been the subject of several important studies in recent years. This review summarises the findings on both plant cell wall and plant immunity, improving our understanding and may provide impetus to various researchers.

Rice cellulose synthase-like protein OsCSLD4 coordinates the trade-off between plant growth and defense

Plant cell wall is a complex and changeable structure, which is very important for plant growth and development. It is clear that cell wall polysaccharide synthases have critical functions in rice growth and abiotic stress, yet their role in plant response to pathogen invasion is poorly understood. Here, we describe a dwarf and narrowed leaf in Hejiang 19 (dnl19) mutant in rice, which shows multiple growth defects such as reduced plant height, enlarged lamina joint angle, curled leaf morphology, and a decrease in panicle length and seed setting. MutMap analysis, genetic complementation and gene knockout mutant show that cellulose synthase-like D4 (OsCSLD4) is the causal gene for DNL19. Loss function of OsCSLD4 leads to a constitutive activation of defense response in rice. After inoculation with rice blast and bacterial blight, dnl19 displays an enhanced disease resistance. Widely targeted metabolomics analysis reveals that disruption of OsCSLD4 in dnl19 resulted in significant increase of L-valine, L-asparagine, L-histidine, L-alanine, gentisic acid, but significant decrease of L-aspartic acid, malic acid, 6-phosphogluconic acid, glucose 6-phosphate, galactose 1-phosphate, gluconic acid, D-aspartic acid. Collectively, our data reveals the importance of OsCSLD4 in balancing the trade-off between rice growth and defense.

Jasmonate Hypersensitive 3 negatively regulates both jasmonate and ethylene-mediated responses in Arabidopsis

Jasmonate (JA) is an important hormone involved in regulating diverse responses to environmental factors as well as growth and development, and its signalling is influenced by other hormones such as ethylene (ET). However, our understanding of the regulatory relationship between the JA and ET signalling pathways is limited. In this study, we isolated an Arabidopsis JA-hypersensitive mutant, jah3 (jasmonate hypersensitive3)-1. Map-based cloning revealed that the JAH3 gene corresponds to At4g16535. JAH3 encodes a protein of unknown function whose amino acid sequence has similarity to leukocyte receptor cluster-like protein. The mutation in jah3-1 is caused by a single nucleotide change from A to T at position 220 of 759 bp. Using CRISPR-Cas9, we generated a second allele, jah3-2, that encodes a truncated protein. Both of these loss-of-function alleles resulted in hypersensitivity to JA, ET-induced root growth inhibition, and accelerated dark-induced senescence. Double mutant analyses employing coronatine insensitive 1 (coi1) and ethylene insensitive 3 (ein3) mutants (jah3 coi1 and jah3 ein3) demonstrated that the hypersensitive phenotypes of the jah3 mutants are mediated by JA and ET signalling components COI1 and EIN3. Therefore, we propose that JAH3 is a negative regulator of both JA and ET signalling.

Advances in S gene targeted genome-editing and its applicability to disease resistance breeding in selected Solanaceae crop plants

Genome-editing tools for the development of traits to tolerate abiotic and biotic adversaries are the recently devised breeding techniques revolutionizing molecular breeding by addressing the issues of rapidness and precision. To that end, disease resistance development by disrupting disease susceptibility genes (S genes) to intervene in the biological mechanism of pathogenicity has significantly improved the techniques of molecular breeding. Despite the achievements in genome-editing aimed at the intervention of the function of susceptibility determinants or gene regulatory elements, off-target effects associated with yield-related traits are still the main setbacks. The challenges are attributed to the complexity of the inheritance of traits controlled by pleiotropic genes. Therefore, a more rigorous genome-editing tool with ultra-precision and efficiency for the development of broad-spectrum and durable disease resistance applied to staple crop plants is of critical importance in molecular breeding programs. The main objective of this article is to review the most impressive progresses achieved in resistance breeding against the main diseases of three Solanaceae crops (potato, Solanum tuberosum; tomato, Solanum lycopersicum and pepper, Capsicum annuum) using genome-editing by disrupting the sequences of S genes, their promoters, or pathogen genes. In this paper, we discussed the complexity and applicability of genome-editing tools, summarized the main disease of Solanaceae crops, and compiled the recent reports on disease resistance developed by S-gene silencing and their off-target effects. Moreover, GO count and gene annotation were made for pooled S-genes from biological databases. Achievements and prospects of S-gene-based next-generation breeding technologies are also discussed.

Most S genes are membrane –anchored and are involved in infection and pre-penetration process

S gene-editing is less likely to cause an off-target effect

Gene-editing has been considered a more acceptable engineering tool

Editing S genes either from the pathogen or host ends has opened new possibilities

Cell Wall Signaling in Plant Development and Defense

Plant architecture fundamentally differs from that of other multicellular organisms in that individual cells serve as osmotic bricks, defined by the equilibrium between the internal turgor pressure and the mechanical resistance of the surrounding cell wall, which constitutes the interface between plant cells and their environment. The state and integrity of the cell wall are constantly monitored by cell wall surveillance pathways, which relay information to the cell interior. A recent surge of discoveries has led to significant advances in both mechanistic and conceptual insights into a multitude of cell wall response pathways that play diverse roles in the development, defense, stress response, and maintenance of structural integrity of the cell. However, these advances have also revealed the complexity of cell wall sensing, and many more questions remain to be answered, for example, regarding the mechanisms of cell wall perception, the molecular players in this process, and how cell wall-related signals are transduced and integrated into cellular behavior. This review provides an overview of the mechanistic and conceptual insights obtained so far and highlights areas for future discoveries in this exciting area of plant biology.

Cellulose accumulation mediated by PbrCSLD5, a cellulose synthase-like protein, results in cessation of pollen tube growth in Pyrus bretschneideri

Cellulose, a key component of the cell wall, plays an important role in maintaining the growth of pollen tubes. However, the molecular mechanism of cellulose participating in the cessation of pear pollen tube growth remains unclear. Here, we reported that at 15 h post-cultured (HPC), the slow-growth pear pollen tubes showed thickened cell walls and cellulose accumulation in the inner wall. Transcriptome data and quantitative real-time PCR analysis showed that PbrCSLD5, a cellulose synthesis-like gene, was highly expressed in the 15 HPC pear pollen tubes. Knockdown of PbrCSLD5 caused a decrease in cellulose content in pear pollen tubes. Moreover, PbrCSLD5 overexpression in Arabidopsis resulted in the accumulation of cellulose and disruption of normal pollen tube growth. Transcription factor PbrMADS52 was found to bind to the promoter of PbrCSLD5 and enhanced its expression. Our results suggested that the PbrMADS52-PbrCSLD5 signaling pathway led to increased cellulose content in the pear pollen tube cell wall, thereby inhibiting pollen tube growth. These results provided new insights into the regulation of pollen tube growth.

Photoprotection contributes to freezing tolerance as revealed by RNA-seq profiling of rhododendron leaves during cold acclimation and deacclimation over time

Cold acclimation (CA) and deacclimation (DA), which are often accompanied by changes in freezing tolerance (FT), carbohydrates and hormones, are crucial for winter survival, especially under global warming. Plants with weak CA and premature DA caused by warm winters and/or unseasonal warm spells can be easily injured by adverse reactions to cold. Thus, understanding the molecular mechanisms of FT is imperative. In this study, we used high-throughput RNA-seq to profile the CA and DA of leaves of overwintering Rhododendron "Miyo-no-Sakae" over time; these leaves do not undergo dormancy but do undergo photoprotection during CA, and they do not grow during DA. Using Mfuzz and weighted gene coexpression network analysis, we identified specific transcriptional characteristics in each phase of CA and DA and proposed networks involving coexpressed genes and physiological traits. In particular, we discovered that the circadian rhythm is critical for obtaining the strongest FT, and high expression of circadian rhythm-related genes might be linked to sugar accumulation during winter. Furthermore, evergreen leaves exhibited robust photoprotection during winter, as revealed by high values of nonphotochemical quenching, high expression of transcripts annotated as "early light-induced proteins", loss of granum stacks and destacking of thylakoids, all of which were alleviated during DA. The strong requirement of photoprotection could be the reason for decreased abscisic acid (ABA) and jasmonic acid (JA) contents during CA, and decreases in ABA and JA contents may contribute to decreases in lignin content. Our data suggest that the molecular mechanisms of FT in overwintering leaves are unique, which may be due to the high requirements for photoprotection during winter.

Integrative transcriptome and proteome analyses provide deep insights into the molecular mechanism of salt tolerance in Limonium bicolor

Integrative transcriptome and proteome analyses revealed many candidate members that may involve in salt secretion from salt glands in Limonium bicolor. Limonium bicolor, a typical recretohalophyte, protects itself from salt damage by excreting excess salt out of its cells through salt glands. Here, to provide an overview of the salt-tolerance mechanism of L. bicolor, we conducted integrative transcriptome and proteome analyses of this species under salt treatment. We identified numerous differentially expressed transcripts and proteins that may be related to the salt-tolerance mechanism of L. bicolor. By measuring the Na⁺ secretion rate, were found that this cation secretion rate of a single salt gland was significantly increased after high salinity treatment compared with that in control and then reached the maximum in a short time. Interestingly, transcripts and proteins involved in transmembrane transport of ions were differentially expressed in response to high salinity treatment, suggesting a number of genes and proteins they may play important roles in the salt-stress response. Correlation between differentially expressed transcript and protein profiles revealed several transcripts and proteins that may be responsible for salt tolerance, such as cellulose synthases and annexins. Our findings uncovered many candidate transcripts and proteins in response to the salt tolerance of L. bicolor, providing deep insights into the molecular mechanisms of this important process in recretohalophytes.

PMR4-dependent cell wall depositions are a consequence but not the cause of temperature-induced autoimmunity

Plants possess a well-balanced immune system that is required for defense against pathogen infections. In autoimmune mutants or necrotic crosses, an intrinsic temperature-dependent imbalance leads to constitutive immune activation, resulting in severe damage or even death of plants. Recently, cell wall depositions were described as one of the symptoms following induction of the autoimmune phenotype in Arabidopsis saul1-1 mutants. However, the regulation and function of these depositions remained unclear. Here, we show that cell wall depositions, containing lignin and callose, were a common autoimmune feature and were deposited in proportion to the severity of the autoimmune phenotype at reduced ambient temperatures. When plants were exposed to reduced temperature for periods insufficient to induce an autoimmune phenotype, the cell wall depositions were not present. After low temperature intervals, sufficient to induce autoimmune responses, cell wall depositions correlated with a point of no return in saul1-1 autoimmunity. Although cell wall depositions were largely abolished in saul1-1 pmr4-1 double mutants lacking SAUL1 and the callose synthase gene GSL5/PMR4, their phenotype remained unchanged compared to that of the saul1-1 single mutant. Our data showed that cell wall depositions generally occur in autoimmunity, but appear not to be the cause of autoimmune phenotypes.

Cell wall associated immunity in plants

The plant cell wall is the first physical and defensive barrier against pathogens. The plant cell wall usually undergoes dynamic remodeling as an immune response to prevent infection by pathogens. In this review, we summarize advances on relationship between cell wall and immunity in plants. In particular, we outline current progresses regarding the regulation of the cell wall components, including cellulose, hemicellulose, pectin and lignin, on plant disease resistance. We also discuss the impacts of cell wall-derived cellodextrin, oligogalacturonic acid and xyloglucan/xylan oligosaccharides as potent elicitors or signal molecules to trigger plant immune response. We further propose future studies on dissecting the molecular regulation of cell wall on plant immunity, which have potentials in practical application of crop breeding aiming at improvement of plant disease resistance.

A primary cell wall cellulose-dependent defense mechanism against vascular pathogens revealed by time-resolved dual transcriptomics

BACKGROUND

Cell walls (CWs) are protein-rich polysaccharide matrices essential for plant growth and environmental acclimation. The CW constitutes the first physical barrier as well as a primary source of nutrients for microbes interacting with plants, such as the vascular pathogen Fusarium oxysporum (Fo). Fo colonizes roots, advancing through the plant primary CWs towards the vasculature, where it grows causing devastation in many crops. The pathogenicity of Fo and other vascular microbes relies on their capacity to reach and colonize the xylem. However, little is known about the root-microbe interaction before the pathogen reaches the vasculature and the role of the plant CW during this process.

RESULTS

Using the pathosystem Arabidopsis-Fo5176, we show dynamic transcriptional changes in both fungus and root during their interaction. One of the earliest plant responses to Fo5176 was the downregulation of primary CW synthesis genes. We observed enhanced resistance to Fo5176 in Arabidopsis mutants impaired in primary CW cellulose synthesis. We confirmed that Arabidopsis roots deposit lignin in response to Fo5176 infection, but we show that lignin-deficient mutants were as susceptible as wildtype plants to Fo5176. Genetic impairment of jasmonic acid biosynthesis and signaling did not alter Arabidopsis response to Fo5176, whereas impairment of ethylene signaling did increase vasculature colonization by Fo5176. Abolishing ethylene signaling attenuated the observed resistance while maintaining the dwarfism observed in primary CW cellulose-deficient mutants.

CONCLUSIONS

Our study provides significant insights on the dynamic root-vascular pathogen interaction at the transcriptome level and the vital role of primary CW cellulose during defense response to these pathogens. These findings represent an essential resource for the generation of plant resistance to Fo that can be transferred to other vascular pathosystems.

With an Ear Up against the Wall: An Update on Mechanoperception in Arabidopsis

Cells interpret mechanical signals and adjust their physiology or development appropriately. In plants, the interface with the outside world is the cell wall, a structure that forms a continuum with the plasma membrane and the cytoskeleton. Mechanical stress from cell wall damage or deformation is interpreted to elicit compensatory responses, hormone signalling, or immune responses. Our understanding of how this is achieved is still evolving; however, we can refer to examples from animals and yeast where more of the details have been worked out. Here, we provide an update on this changing story with a focus on candidate mechanosensitive channels and plasma membrane-localized receptors.

Immune Priming Triggers Cell Wall Remodeling and Increased Resistance to Halo Blight Disease in Common Bean

The cell wall (CW) is a dynamic structure extensively remodeled during plant growth and under stress conditions, however little is known about its roles during the immune system priming, especially in crops. In order to shed light on such a process, we used the Phaseolus vulgaris-Pseudomonas syringae (Pph) pathosystem and the immune priming capacity of 2,6-dichloroisonicotinic acid (INA). In the first instance we confirmed that INA-pretreated plants were more resistant to Pph, which was in line with the enhanced production of H₂O₂ of the primed plants after elicitation with the peptide flg22. Thereafter, CWs from plants subjected to the different treatments (non- or Pph-inoculated on non- or INA-pretreated plants) were isolated to study their composition and properties. As a result, the Pph inoculation modified the bean CW to some extent, mostly the pectic component, but the CW was as vulnerable to enzymatic hydrolysis as in the case of non-inoculated plants. By contrast, the INA priming triggered a pronounced CW remodeling, both on the cellulosic and non-cellulosic polysaccharides, and CW proteins, which resulted in a CW that was more resistant to enzymatic hydrolysis. In conclusion, the increased bean resistance against Pph produced by INA priming can be explained, at least partially, by a drastic CW remodeling.

Updating Insights into the Catalytic Domain Properties of Plant Cellulose synthase (CesA) and Cellulose synthase-like (Csl) Proteins

The wall is the last frontier of a plant cell involved in modulating growth, development and defense against biotic stresses. Cellulose and additional polysaccharides of plant cell walls are the most abundant biopolymers on earth, having increased in economic value and thereby attracted significant interest in biotechnology. Cellulose biosynthesis constitutes a highly complicated process relying on the formation of cellulose synthase complexes. Cellulose synthase (CesA) and Cellulose synthase-like (Csl) genes encode enzymes that synthesize cellulose and most hemicellulosic polysaccharides. Arabidopsis and rice are invaluable genetic models and reliable representatives of land plants to comprehend cell wall synthesis. During the past two decades, enormous research progress has been made to understand the mechanisms of cellulose synthesis and construction of the plant cell wall. A plethora of cesa and csl mutants have been characterized, providing functional insights into individual protein isoforms. Recent structural studies have uncovered the mode of CesA assembly and the dynamics of cellulose production. Genetics and structural biology have generated new knowledge and have accelerated the pace of discovery in this field, ultimately opening perspectives towards cellulose synthesis manipulation. This review provides an overview of the major breakthroughs gathering previous and recent genetic and structural advancements, focusing on the function of CesA and Csl catalytic domain in plants.

Arabidopsis cell wall composition determines disease resistance specificity and fitness

Plant cells are surrounded by an extracellular matrix known as the cell wall. We have analyzed the contribution of the Arabidopsis cell wall to disease resistance to pathogens with different parasitic styles. Here, we demonstrate that plant cell walls are determinants of immune responses since modification of their composition in a set of Arabidopsis cell wall mutants has an impact on their disease resistance and fitness phenotypes. In these genotypes, we identified specific correlations between the amounts of specific wall carbohydrate epitopes and disease resistance/fitness phenotypes through mathematical analyses. These data support the relevant and specific function of plant cell wall composition in plant immune responses and provide the basis for using wall traits in crop breeding programs.

Plant cell walls are complex structures subject to dynamic remodeling in response to developmental and environmental cues and play essential functions in disease resistance responses. We tested the specific contribution of plant cell walls to immunity by determining the susceptibility of a set of Arabidopsis cell wall mutants (cwm) to pathogens with different parasitic styles: a vascular bacterium, a necrotrophic fungus, and a biotrophic oomycete. Remarkably, most cwm mutants tested (29/34; 85.3%) showed alterations in their resistance responses to at least one of these pathogens in comparison to wild-type plants, illustrating the relevance of wall composition in determining disease-resistance phenotypes. We found that the enhanced resistance of cwm plants to the necrotrophic and vascular pathogens negatively impacted cwm fitness traits, such as biomass and seed yield. Enhanced resistance of cwm plants is not only mediated by canonical immune pathways, like those modulated by phytohormones or microbe-associated molecular patterns, which are not deregulated in the cwm tested. Pectin-enriched wall fractions isolated from cwm plants triggered immune responses in wild-type plants, suggesting that wall-mediated defensive pathways might contribute to cwm resistance. Cell walls of cwm plants show a high diversity of composition alterations as revealed by glycome profiling that detect specific wall carbohydrate moieties. Mathematical analysis of glycome profiling data identified correlations between the amounts of specific wall carbohydrate moieties and disease resistance phenotypes of cwm plants. These data support the relevant and specific function of plant wall composition in plant immune response modulation and in balancing disease resistance/development trade-offs.

Comparative transcriptomic analysis of seed coats with high and low lignin contents reveals lignin and flavonoid biosynthesis in Brassica napus

BACKGROUND

Brassica napus L. (2n = 38, AACC) is one of the most important oil crops and sources of protein for animal feed worldwide. Lignin is a large molecule aromatic polymer and a major cell wall component. However, lignin in the seed coat reduces the availability and restricts the development of rapeseed cake. Therefore, it is critical to reduce the lignin content of the seed coat. Here, high-lignin (H-lignin) and low-lignin (L-lignin) content recombinant inbred lines (RILs) were selected from an RIL population for analysis.

RESULTS

The cross-section results indicated that the seed coat of the H-lignin lines was thicker than that of the L-lignin lines, especially the palisade layer. The seed coats and embryos at 35, 40 and 46 days after flowering (DAF) were subjected to RNA sequencing (RNA-Seq), and the expression of the BnPAL and BnC4H gene families in the lignin pathway was significantly higher in the H-lignin seed coat than in the L-lignin seed coat. The Bn4CL gene family also showed this trend. In addition, among the genes related to plant hormone synthesis, BnaC02g01710D was upregulated and BnaA07g11700D and BnaC09g00190D were downregulated in H-lignin lines. Some transcription factors were upregulated, such as BnNAC080, BnNAC083, BnMYB9, BnMYB9-1, BnMYB60 and BnMYB60-1, while BnMYB91 was downregulated in H-lignin lines. Moreover, most genes of the flavonoid pathway, such as BnCHS and BnDFR, were strongly expressed in H-lignin seed coat.

CONCLUSIONS

In Our study, some key genes such as hormone synthesis genes, transcription factors and miRNAs related to lignin and flavonoid biosynthesis were identified. A regulatory model of B. napus seed coat lignin was proposed. These results provide new insight into lignin and flavonoid biosynthesis in B. napus.

GhMYB4 downregulates lignin biosynthesis and enhances cotton resistance to Verticillium dahliae

GhMYB4 acts as a negative regulator in lignin biosynthesis, which results in alteration of cell wall integrity and activation of cotton defense response. Verticillium wilt of cotton (Gossypium hirsutum) caused by the soil-borne fungus Verticillium dahliae (V. dahliae) represents one of the most important constraints of cotton production worldwide. Mining of the genes involved in disease resistance and illuminating the molecular mechanisms that underlie this resistance is of great importance in cotton breeding programs. Defense-induced lignification in plants is necessary for innate immunity, and there are reports of a correlation between increased lignification and disease resistance. In this study, we present an example in cotton whereby plants with reduced lignin content also exhibit enhanced disease resistance. We identified a negative regulator of lignin synthesis, in cotton encoded in GhMYB4. Overexpression of GhMYB4 in cotton and Arabidopsis enhanced resistance to V. dahliae  with reduced lignin deposition. Moreover, GhMYB4 could bind the promoters of several genes involved in lignin synthesis, such as GhC4H-1, GhC4H-2, Gh4CL-4, and GhCAD-3, and impair their expression. The reduction of lignin content in GhMYB4-overexpressing cotton led to alterations of cell wall integrity (CWI) and released more oligogalacturonides (OGs) which may act as damage-associated molecular patterns (DAMPs) to stimulate plant defense responses. In support of this hypothesis, exogenous application with polygalacturonic acid (PGA) in cotton activated biosynthesis of jasmonic acid (JA) and JA-mediated defense against V. dahliae, similar to that described for cotton plants overexpressing GhMYB4. This study provides a new candidate gene for cotton disease-resistant breeding and an increased understanding of the relationship between lignin synthesis, OG release, and plant immunity.

Formin nanoclustering-mediated actin assembly during plant flagellin and DSF signaling

Plants respond to bacterial infection acutely with actin remodeling during plant immune responses. The mechanisms by which bacterial virulence factors (VFs) modulate plant actin polymerization remain enigmatic. Here, we show that plant-type-I formin serves as the molecular sensor for actin remodeling in response to two bacterial VFs: Xanthomonas campestris pv. campestris (Xcc) diffusible signal factor (DSF), and pathogen-associated molecular pattern (PAMP) flagellin in pattern-triggered immunity (PTI). Both VFs regulate actin assembly by tuning the clustering and nucleation activity of formin on the plasma membrane (PM) at the nano-sized scale. By being integrated within the cell-wall-PM-actin cytoskeleton (CW-PM-AC) continuum, the dynamic behavior and function of formins are highly dependent on each scaffold layer's composition within the CW-PM-AC continuum during both DSF and PTI signaling. Our results reveal a central mechanism for rapid actin remodeling during plant-bacteria interactions, in which bacterial signaling molecules fine tune plant formin nanoclustering in a host mechanical-structure-dependent manner.

Host Cell Wall Damage during Pathogen Infection: Mechanisms of Perception and Role in Plant-Pathogen Interactions

The plant cell wall (CW) is a complex structure that acts as a mechanical barrier, restricting the access to most microbes. Phytopathogenic microorganisms can deploy an arsenal of CW-degrading enzymes (CWDEs) that are required for virulence. In turn, plants have evolved proteins able to inhibit the activity of specific microbial CWDEs, reducing CW damage and favoring the accumulation of CW-derived fragments that act as damage-associated molecular patterns (DAMPs) and trigger an immune response in the host. CW-derived DAMPs might be a component of the complex system of surveillance of CW integrity (CWI), that plants have evolved to detect changes in CW properties. Microbial CWDEs can activate the plant CWI maintenance system and induce compensatory responses to reinforce CWs during infection. Recent evidence indicates that the CWI surveillance system interacts in a complex way with the innate immune system to fine-tune downstream responses and strike a balance between defense and growth.

Arabidopsis cell wall composition determines disease resistance specificity and fitness

Plant cell walls are complex structures subject to dynamic remodeling in response to developmental and environmental cues and play essential functions in disease resistance responses. We tested the specific contribution of plant cell walls to immunity by determining the susceptibility of a set of Arabidopsis cell wall mutants (cwm) to pathogens with different parasitic styles: a vascular bacterium, a necrotrophic fungus, and a biotrophic oomycete. Remarkably, most cwm mutants tested (29/34; 85.3%) showed alterations in their resistance responses to at least one of these pathogens in comparison to wild-type plants, illustrating the relevance of wall composition in determining disease-resistance phenotypes. We found that the enhanced resistance of cwm plants to the necrotrophic and vascular pathogens negatively impacted cwm fitness traits, such as biomass and seed yield. Enhanced resistance of cwm plants is not only mediated by canonical immune pathways, like those modulated by phytohormones or microbe-associated molecular patterns, which are not deregulated in the cwm tested. Pectin-enriched wall fractions isolated from cwm plants triggered immune responses in wild-type plants, suggesting that wall-mediated defensive pathways might contribute to cwm resistance. Cell walls of cwm plants show a high diversity of composition alterations as revealed by glycome profiling that detect specific wall carbohydrate moieties. Mathematical analysis of glycome profiling data identified correlations between the amounts of specific wall carbohydrate moieties and disease resistance phenotypes of cwm plants. These data support the relevant and specific function of plant wall composition in plant immune response modulation and in balancing disease resistance/development trade-offs.

Jasmonate biosynthesis arising from altered cell walls is prompted by turgor-driven mechanical compression

Despite the vital roles of jasmonoyl-isoleucine (JA-Ile) in governing plant growth and environmental acclimation, it remains unclear what intracellular processes lead to its induction. Here, we provide compelling genetic evidence that mechanical and osmotic regulation of turgor pressure represents a key elicitor of JA-Ile biosynthesis. After identifying cell wall mutant alleles in KORRIGAN1 (KOR1) with elevated JA-Ile in seedling roots, we found that ectopic JA-Ile resulted from cell nonautonomous signals deriving from enlarged cortex cells compressing inner tissues and stimulating JA-Ile production. Restoring cortex cell size by cell type-specific KOR1 complementation, by isolating a genetic kor1 suppressor, and by lowering turgor pressure with hyperosmotic treatments abolished JA-Ile signaling. Conversely, hypoosmotic treatment activated JA-Ile signaling in wild-type plants. Furthermore, constitutive JA-Ile levels guided mutant roots toward greater water availability. Collectively, these findings enhance our understanding on JA-Ile biosynthesis initiation and reveal a previously undescribed role of JA-Ile in orchestrating environmental resilience.

Regulation of Sixth Seminal Root Formation by Jasmonate in Triticum aestivum L

A well-developed root system is an important characteristic of crop plants, which largely determines their productivity, especially under conditions of water and nutrients deficiency. Being Poaceous, wheat has more than one seminal root. The number of grown seminal roots varies in different wheat accessions and is regulated by environmental factors. Currently, the molecular mechanisms determining the number of germinated seminal roots remain poorly understood. The analysis of the root system development in germinating seeds of genetically modified hexaploid wheat plants with altered activity of jasmonate biosynthesis pathway and seeds exogenously treated with methyl jasmonate revealed the role of jasmonates in the regulation of sixth seminal root development. This regulatory effect strongly depends on the jasmonate concentration and the duration of the exposure to this hormone. The maximum stimulatory effect of exogenously applied methyl jasmonate on the formation of the sixth seminal root was achieved at 200 μM concentration after 48 h of treatment. Further increase in concentration and exposure time does not increase the stimulating effect. While 95% of non-transgenic plants under non-stress conditions possess five or fewer seminal roots, the number of plants with developed sixth seminal root reaches up to 100% when selected transgenic lines are treated with methyl jasmonate.

Nitrogen Supply Alters Rice Defense Against the Striped Stem Borer Chilo suppressalis

Plant nutrition status is closely associated with plant defense against insect herbivores. However, the way nitrogen supply regulates rice anti-herbivore is not clear. This study investigated the effects of low (LN, 0.3 mM) and high (HN, 3 mM) nitrate levels on rice resistance against the striped stem borer Chilo suppressalis (SSB), one of the major destructive rice pests. Seven-day-old rice seedlings were cultured with different nitrate levels for 30 days and then inoculated with third instars of SSB. LN significantly enhanced rice anti-herbivore defense and lowered the total nitrogen content in the plants, but increased the content of free amino acids after SSB infestation. Additionally, LN significantly increased the accumulation of phenolic acids and flavonoids, especially lignin, resulting in enhanced constitutive defense in SSB-infested plants. SSB feeding led to a rapid accumulation of secondary metabolites. HN application led to the accumulation of metabolites derived from cinnamic acid, p-coumaric acid, p-coumaric CoA, feruloyl CoA, and apigenin, while LN led to the accumulation of metabolites derived from 3-dehydroquinic acid, phenylalanine, acetyl CoA, and aspartic acid. Collectively, our finding suggests that nitrogen deficiency enhances rice anti-herbivore defense via constitutive defense by the accumulation of phenolic acids and flavonoids.

Impaired Cuticle Functionality and Robust Resistance to Botrytis cinerea in Arabidopsis thaliana Plants With Altered Homogalacturonan Integrity Are Dependent on the Class III Peroxidase AtPRX71

Pectin is a major cell wall component that plays important roles in plant development and response to environmental stresses. Arabidopsis thaliana plants expressing a fungal polygalacturonase (PG plants) that degrades homogalacturonan (HG), a major pectin component, as well as loss-of-function mutants for QUASIMODO2 (QUA2), encoding a putative pectin methyltransferase important for HG biosynthesis, show accumulation of reactive oxygen species (ROS), reduced growth and almost complete resistance to the fungal pathogen Botrytis cinerea. Both PG and qua2 plants show increased expression of the class III peroxidase AtPRX71 that contributes to their elevated ROS levels and reduced growth. In this work, we show that leaves of PG and qua2 plants display greatly increased cuticle permeability. Both increased cuticle permeability and resistance to B. cinerea in qua2 are suppressed by loss of AtPRX71. Increased cuticle permeability in qua2, rather than on defects in cuticle ultrastructure or cutin composition, appears to be dependent on reduced epidermal cell adhesion, which is exacerbated by AtPRX71, and is suppressed by the esmeralda1 mutation, which also reverts the adhesion defect and the resistant phenotype. Increased cuticle permeability, accumulation of ROS, and resistance to B. cinerea are also observed in mutants lacking a functional FERONIA, a receptor-like kinase thought to monitor pectin integrity. In contrast, mutants with defects in other structural components of primary cell wall do not have a defective cuticle and are normally susceptible to the fungus. Our results suggest that disrupted cuticle integrity, mediated by peroxidase-dependent ROS accumulation, plays a major role in the robust resistance to B. cinerea of plants with altered HG integrity.

PHOTO-SENSITIVE LEAF ROLLING 1 encodes a polygalacturonase that modifies cell wall structure and drought tolerance in rice

The biosynthesis and modification of cell wall composition and structure are controlled by hundreds of enzymes and have a direct consequence on plant growth and development. However, the majority of these enzymes has not been functionally characterised. Rice mutants with leaf-rolling phenotypes were screened in a field. Phenotypic analysis under controlled conditions was performed for the selected mutant and the relevant gene was identified by map-based cloning. Cell wall composition was analysed by glycome profiling assay. We identified a photo-sensitive leaf rolling 1 (psl1) mutant with 'napping' (midday depression of photosynthesis) phenotype and reduced growth. The PSL1 gene encodes a cell wall-localised polygalacturonase (PG), a pectin-degrading enzyme. psl1 with a 260-bp deletion in its gene displayed leaf rolling in response to high light intensity and/or low humidity. Biochemical assays revealed PG activity of recombinant PSL1 protein. Significant modifications to cell wall composition in the psl1 mutant compared with the wild-type plants were identified. Such modifications enhanced drought tolerance of the mutant plants by reducing water loss under osmotic stress and drought conditions. Taken together, PSL1 functions as a PG that modifies cell wall biosynthesis, plant development and drought tolerance in rice.

Highly dynamic, coordinated, and stage-specific profiles are revealed by a multi-omics integrative analysis during tuberous root development in cassava

Cassava (Manihot esculenta) is an important starchy root crop that provides food for millions of people worldwide, but little is known about the regulation of the development of its tuberous root at the multi-omics level. In this study, the transcriptome, proteome, and metabolome were examined in parallel at seven time-points during the development of the tuberous root from the early to late stages of its growth. Overall, highly dynamic and stage-specific changes in the expression of genes/proteins were observed during development. Cell wall and auxin genes, which were regulated exclusively at the transcriptomic level, mainly functioned during the early stages. Starch biosynthesis, which was controlled at both the transcriptomic and proteomic levels, was mainly activated in the early stages and was greatly restricted during the late stages. Two main branches of lignin biosynthesis, coniferyl alcohol and sinapyl alcohol, also functioned during the early stages of development at both the transcriptomic and proteomic levels. Metabolomic analysis further supported the stage-specific roles of particular genes/proteins. Metabolites related to lignin and flavonoid biosynthesis showed high abundance during the early stages, those related to lipids exhibited high abundance at both the early and middle stages, while those related to amino acids were highly accumulated during the late stages. Our findings provide a comprehensive resource for broadening our understanding of tuberous root development and will facilitate future genetic improvement of cassava.

Associations between phytohormones and cellulose biosynthesis in land plants

BACKGROUND

Phytohormones are small molecules that regulate virtually every aspect of plant growth and development, from basic cellular processes, such as cell expansion and division, to whole plant environmental responses. While the phytohormone levels and distribution thus tell the plant how to adjust itself, the corresponding growth alterations are actuated by cell wall modification/synthesis and internal turgor. Plant cell walls are complex polysaccharide-rich extracellular matrixes that surround all plant cells. Among the cell wall components, cellulose is typically the major polysaccharide, and is the load-bearing structure of the walls. Hence, the cell wall distribution of cellulose, which is synthesized by large Cellulose Synthase protein complexes at the cell surface, directs plant growth.

SCOPE

Here, we review the relationships between key phytohormone classes and cellulose deposition in plant systems. We present the core signalling pathways associated with each phytohormone and discuss the current understanding of how these signalling pathways impact cellulose biosynthesis with a particular focus on transcriptional and post-translational regulation. Because cortical microtubules underlying the plasma membrane significantly impact the trajectories of Cellulose Synthase Complexes, we also discuss the current understanding of how phytohormone signalling impacts the cortical microtubule array.

CONCLUSION

Given the importance of cellulose deposition and phytohormone signalling in plant growth and development, one would expect that there is substantial cross-talk between these processes; however, mechanisms for many of these relationships remain unclear and should be considered as the target of future studies.

Molecular and physiological mechanisms underlying magnesium-deficiency-induced enlargement, cracking and lignification of Citrus sinensis leaf veins

Little is known about the physiological and molecular mechanisms underlying magnesium (Mg)-deficiency-induced enlargement, cracking and lignification of midribs and main lateral veins of Citrus leaves. Citrus sinensis (L.) Osbeck seedlings were irrigated with nutrient solution at a concentration of 0 (Mg-deficiency) or 2 (Mg-sufficiency) mM Mg(NO3)2 for 16 weeks. Enlargement, cracking and lignification of veins occurred only in lower leaves, but not in upper leaves. Total soluble sugars (glucose + fructose + sucrose), starch and cellulose concentrations were less in Mg-deficiency veins of lower leaves (MDVLL) than those in Mg-sufficiency veins of lower leaves (MSVLL), but lignin concentration was higher in MDVLL than that in MSVLL. However, all four parameters were similar between Mg-deficiency veins of upper leaves (MDVUL) and Mg-sufficiency veins of upper leaves (MSVUL). Using label-free, liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, we identified 1229 and 492 differentially abundant proteins (DAPs) in MDVLL vs MSVLL and MDVUL vs MSVUL, respectively. Magnesium-deficiency-induced alterations of Mg, nonstructural carbohydrates, cell wall components, and protein profiles were greater in veins of lower leaves than those in veins of upper leaves. The increased concentration of lignin in MDVLL vs MSVLL might be caused by the following factors: (i) repression of cellulose and starch accumulation promoted lignin biosynthesis; (ii) abundances of proteins involved in phenylpropanoid biosynthesis pathway, hormone biosynthesis and glutathione metabolism were increased; and (iii) the abundances of the other DAPs [viz., copper/zinc-superoxide dismutase, ascorbate oxidase (AO) and ABC transporters] involved in lignin biosynthesis were elevated. Also, the abundances of several proteins involved in cell wall metabolism (viz., expansins, Rho GTPase-activating protein gacA, AO, monocopper oxidase-like protein and xyloglucan endotransglucosylase/hydrolase) were increased in MDVLL vs MSVLL, which might be responsible for the enlargement and cracking of leaf veins.

Arabinoxylan-Oligosaccharides Act as Damage Associated Molecular Patterns in Plants Regulating Disease Resistance

Immune responses in plants can be triggered by damage/microbe-associated molecular patterns (DAMPs/MAMPs) upon recognition by plant pattern recognition receptors (PRRs). DAMPs are signaling molecules synthesized by plants or released from host cellular structures (e.g., plant cell walls) upon pathogen infection or wounding. Despite the hypothesized important role of plant cell wall-derived DAMPs in plant-pathogen interactions, a very limited number of these DAMPs are well characterized. Recent work demonstrated that pectin-enriched cell wall fractions extracted from the cell wall mutant impaired in Arabidopsis Response Regulator 6 (arr6), that showed altered disease resistance to several pathogens, triggered more intense immune responses than those activated by similar cell wall fractions from wild-type plants. It was hypothesized that arr6 cell wall fractions could be differentially enriched in DAMPs. In this work, we describe the characterization of the previous immune-active fractions of arr6 showing the highest triggering capacities upon further fractionation by chromatographic means. These analyses pointed to a role of pentose-based oligosaccharides triggering plant immune responses. The characterization of several pentose-based oligosaccharide structures revealed that β-1,4-xylooligosaccharides of specific degrees of polymerization and carrying arabinose decorations are sensed as DAMPs by plants. Moreover, the pentasaccharide 33-α-L-arabinofuranosyl-xylotetraose (XA3XX) was found as a highly active DAMP structure triggering strong immune responses in Arabidopsis thaliana and enhancing crop disease resistance.

The LRXs-RALFs-FER module controls plant growth and salt stress responses by modulating multiple plant hormones

Salt stress is a major environmental factor limiting plant growth and productivity. We recently discovered an important new salt tolerance pathway, where the cell wall leucine-rich repeat extensins LRX3/4/5, the RAPID ALKALINIZATION FACTOR (RALF) peptides RALF22/23 and receptor-like kinase FERONIA (FER) function as a module to simultaneously regulate plant growth and salt stress tolerance. However, the intracellular signaling pathways that are regulated by the extracellular LRX3/4/5-RALF22/23-FER module to coordinate growth, cell wall integrity and salt stress responses are still unknown. Here, we report that the LRX3/4/5-RALF22/23-FER module negatively regulates the levels of jasmonic acid (JA), salicylic acid (SA) and abscisic acid (ABA). Blocking JA pathway rescues the dwarf phenotype of the lrx345 and fer-4 mutants, while disruption of ABA biosynthesis suppresses the salt-hypersensitivity of these mutants. Many salt stress-responsive genes display abnormal expression patterns in the lrx345 and fer-4 mutants, as well as in the wild type plants treated with epigallocatechin gallate (EGCG), an inhibitor of pectin methylesterases, suggesting cell wall integrity as a critical factor that determines the expression pattern of stress-responsive genes. Production of reactive oxygen species (ROS) is constitutively increased in the lrx345 and fer-4 mutants, and inhibition of ROS accumulation suppresses the salt-hypersensitivity of these mutants. Together, our work provides strong evidence that the LRX3/4/5-RALF22/23-FER module controls plant growth and salt stress responses by regulating hormonal homeostasis and ROS accumulation.

Comparative Transcriptome Analysis of Two Contrasting Soybean Varieties in Response to Aluminum Toxicity

: Aluminum (Al) toxicity is a major factor limiting crop productivity on acid soils. Soybean (Glycine max) is an important oil crop and there is great variation in Al tolerance in soybean germplasms. However, only a few Al-tolerance genes have been reported in soybean. Therefore, the purpose of this study was to identify candidate Al tolerance genes by comparative transcriptome analysis of two contrasting soybean varieties in response to Al stress. Two soybean varieties, M90-24 (M) and Pella (P), which showed significant difference in Al tolerance, were used for RNA-seq analysis. We identified a total of 354 Al-tolerance related genes, which showed up-regulated expression by Al in the Al-tolerant soybean variety M and higher transcript levels in M than P under Al stress. These genes were enriched in the Gene Ontology (GO) terms of cellular glucan metabolic process and regulation of transcription. Five out of 11 genes in the enriched GO term of cellular glucan metabolic process encode cellulose synthases, and one cellulose synthase gene (Glyma.02G205800) was identified as the key hub gene by co-expression network analysis. Furthermore, treatment of soybean roots with a cellulose biosynthesis inhibitor decreased the Al tolerance, indicating an important role of cellulose production in soybean tolerance to Al toxicity. This study provides a list of candidate genes for further investigation on Al tolerance mechanisms in soybean.

Genome-wide analyses of banana fasciclin-like AGP genes and their differential expression under low-temperature stress in chilling sensitive and tolerant cultivars

Thirty MaFLAs vary in their molecular features. MaFLA14/18/27/29 are likely to be involved in banana chilling tolerance by facilitating the cold signaling pathway and enhancing the cell wall biosynthesis. Although several studies have identified the molecular functions of individual fasciclin-like arabinogalactan protein (FLA) genes in plant growth and development, little information is available on their involvement in plant tolerance to low-temperature (LT) stress, and the related underlying mechanism is far from clear. In this study, the different expression of FLAs of banana (Musa acuminata) (MaFLAs) in the chilling-sensitive (CS) and chilling-tolerant (CT) banana cultivars under natural LT was investigated. Based on the latest banana genome database, a genome-wide identification of this gene family was done and the molecular features were analyzed. Thirty MaFLAs were distributed in 10 out of 11 chromosomes and these clustered into four major phylogenetic groups based on shared gene structure. Twenty-four MaFLAs contained N-terminal signal, 19 possessed predicted glycosylphosphatidylinositol (GPI), while 16 had both. Most MaFLAs were downregulated by LT stress. However, MaFLA14/18/29 were upregulated by LT in both cultivars with higher expression level recorded in the CT cultivar. Interestingly, MaFLA27 was significantly upregulated in the CT cultivar, but the opposite occurred for the CS cultivar. MaFLA27 possessed only N-terminal signal, MaFLA18 contained only GPI anchor, MaFLA29 possessed both, while MaFLA14 had neither. Thus, it was suggested that the accumulation of these FLAs in banana under LT could improve banana chilling tolerance through facilitating cold signal pathway and thereafter enhancing biosynthesis of plant cell wall components. The results provide background information of MaFLAs, suggest their involvement in plant chilling tolerance and their potential as candidate genes to be targeted when breeding CT banana.

Plant cell wall integrity maintenance in model plants and crop species-relevant cell wall components and underlying guiding principles

The walls surrounding the cells of all land-based plants provide mechanical support essential for growth and development as well as protection from adverse environmental conditions like biotic and abiotic stress. Composition and structure of plant cell walls can differ markedly between cell types, developmental stages and species. This implies that wall composition and structure are actively modified during biological processes and in response to specific functional requirements. Despite extensive research in the area, our understanding of the regulatory processes controlling active and adaptive modifications of cell wall composition and structure is still limited. One of these regulatory processes is the cell wall integrity maintenance mechanism, which monitors and maintains the functional integrity of the plant cell wall during development and interaction with environment. It is an important element in plant pathogen interaction and cell wall plasticity, which seems at least partially responsible for the limited success that targeted manipulation of cell wall metabolism has achieved so far. Here, we provide an overview of the cell wall polysaccharides forming the bulk of plant cell walls in both monocotyledonous and dicotyledonous plants and the effects their impairment can have. We summarize our current knowledge regarding the cell wall integrity maintenance mechanism and discuss that it could be responsible for several of the mutant phenotypes observed.

The expression characteristics of methyl jasmonate biosynthesis-related genes in Cymbidium faberi and influence of heterologous expression of CfJMT in Petunia hybrida

Cymbidium faberi Rolfe (Orchidaceae) is an herbaceous plant native to China, where it has a long history of cultivation owing to its beautiful flower pattern and floral fragrance. Previously, we conducted a transcriptome analysis of the flower and vegetative buds to elucidate the mechanisms of flower development in C. faberi. In the present study, we found nine secondary metabolic pathways through the KEGG pathway database that were related to the biosynthesis of methyl jasmonate (MeJA) and other volatile organic compounds. qRT-PCR was performed to analyze the expression levels of four key genes in the MeJA pathway. Among these, CfJMT (jasmonic acid carboxyl methyltransferase) had higher transcript levels in sepals, petals and labella than in other tissues. CfJMT was cloned from the petals of full-bloom flowers of C. faberi. The predicted CfJMT protein sequence contains conserved jasmonic acid methyl transferase-7 domains, indicating that it belongs to the SABATH protein family. The CfJMT coding sequence driven by the CaMV35S promoter was successfully transformed into Petunia hybrida through an Agrobacterium-mediated method. Although MeJA could not be detected in either wild-type or transgenic petunia plants, the leaves of the transgenic plants were smaller than those of wild-type plants and pollen development was abnormal. These results indicate that heterologous expression of CfJMT may change the levels of endogenous jasmonic acid and other hormones, but that the content of MeJA is not increased significantly by transformation with CfJMT alone. Thus, other related genes and regulation factors may play important roles in this process.