AtCSLD3 and GhCSLD3 mediate root growth and cell elongation downstream of the ethylene response pathway in Arabidopsis

GhXB38D represses cotton fibre elongation through ubiquitination of ethylene biosynthesis enzymes GhACS4 and GhACO1

Ethylene plays an essential role in the development of cotton fibres. Ethylene biosynthesis in plants is elaborately regulated by the activities of key enzymes, 1-aminocyclopropane-1-carboxylate oxidase (ACO) and 1-aminocyclopropane-1-carboxylate synthase (ACS); however, the potential mechanism of post-translational modification of ACO and ACS to control ethylene synthesis in cotton fibres remains unclear. Here, we identify an E3 ubiquitin ligase, GhXB38D, that regulates ethylene biosynthesis during fibre elongation in cotton. GhXB38D gene is highly expressed in cotton fibres during the rapid elongation stage. Suppressing GhXB38D expression in cotton significantly enhanced fibre elongation and length, accompanied by the up-regulation of genes associated with ethylene signalling and fibre elongation. We demonstrated that GhXB38D interacts with the ethylene biosynthesis enzymes GhACS4 and GhACO1 in elongating fibres and specifically mediates their ubiquitination and degradation. The inhibition of GhXB38D gene expression increased the stability of GhACS4 and GhACO1 proteins in cotton fibres and ovules, resulting in an elevated concentration of ethylene. Our findings highlight the role of GhXB38D as a regulator of ethylene synthesis by ubiquitinating ACS4 and ACO1 proteins and modulating their stability. GhXB38D acts as a negative regulator of fibre elongation and serves as a potential target for enhancing cotton fibre yield and quality through gene editing strategy.

A comprehensive overview of cotton genomics, biotechnology and molecular biological studies

Cotton is an irreplaceable economic crop currently domesticated in the human world for its extremely elongated fiber cells specialized in seed epidermis, which makes it of high research and application value. To date, numerous research on cotton has navigated various aspects, from multi-genome assembly, genome editing, mechanism of fiber development, metabolite biosynthesis, and analysis to genetic breeding. Genomic and 3D genomic studies reveal the origin of cotton species and the spatiotemporal asymmetric chromatin structure in fibers. Mature multiple genome editing systems, such as CRISPR/Cas9, Cas12 (Cpf1) and cytidine base editing (CBE), have been widely used in the study of candidate genes affecting fiber development. Based on this, the cotton fiber cell development network has been preliminarily drawn. Among them, the MYB-bHLH-WDR (MBW) transcription factor complex and IAA and BR signaling pathway regulate the initiation; various plant hormones, including ethylene, mediated regulatory network and membrane protein overlap fine-regulate elongation. Multistage transcription factors targeting CesA 4, 7, and 8 specifically dominate the whole process of secondary cell wall thickening. And fluorescently labeled cytoskeletal proteins can observe real-time dynamic changes in fiber development. Furthermore, research on the synthesis of cotton secondary metabolite gossypol, resistance to diseases and insect pests, plant architecture regulation, and seed oil utilization are all conducive to finding more high-quality breeding-related genes and subsequently facilitating the cultivation of better cotton varieties. This review summarizes the paramount research achievements in cotton molecular biology over the last few decades from the above aspects, thereby enabling us to conduct a status review on the current studies of cotton and provide strong theoretical support for the future direction.

Chitinase-Like Protein PpCTL1 Contributes to Maintaining Fruit Firmness by Affecting Cellulose Biosynthesis during Peach Development

The firmness of the flesh fruit is a very important feature in the eating process. Peach fruit is very hard during development, but its firmness slightly decreases in the later stages of development. While there has been extensive research on changes in cell wall polysaccharides during fruit ripening, little is known about the changes that occur during growth and development. In this study, we investigated the modifications in cell wall components throughout the development and ripening of peach fruit, as well as its impact on firmness. Our findings revealed a significant positive correlation between fruit firmness and cellulose content at development stage. However, the correlation was lost during the softening process, suggesting that cellulose might be responsible for the fruit firmness during development. Members of the chitinase-like protein (CTL) group are of interest because of their possible role in plant cell wall biosynthesis. Here, two CTL homologous genes, PpCTL1 and PpCTL2, were identified in peach. Spatial and temporal expression patterns of PpCTLs revealed that PpCTL1 exhibited high expression abundance in the fruit and followed a similar trend to cellulose during fruit growth. Furthermore, silencing PpCTL1 expression resulted in reduced cellulose content at 5 DAI (days after injection), this change that would have a negative effect on fruit firmness. Our results indicate that PpCTL1 plays an important role in cellulose biosynthesis and the maintenance of peach firmness during development.

Cellulose synthase-like D movement in the plasma membrane requires enzymatic activity

Cellulose Synthase-Like D (CSLD) proteins, important for tip growth and cell division, are known to generate β-1,4-glucan. However, whether they are propelled in the membrane as the glucan chains they produce assemble into microfibrils is unknown. To address this, we endogenously tagged all eight CSLDs in Physcomitrium patens and discovered that they all localize to the apex of tip-growing cells and to the cell plate during cytokinesis. Actin is required to target CSLD to cell tips concomitant with cell expansion, but not to cell plates, which depend on actin and CSLD for structural support. Like Cellulose Synthase (CESA), CSLD requires catalytic activity to move in the plasma membrane. We discovered that CSLD moves significantly faster, with shorter duration and less linear trajectories than CESA. In contrast to CESA, CSLD movement was insensitive to the cellulose synthesis inhibitor isoxaben, suggesting that CSLD and CESA function within different complexes possibly producing structurally distinct cellulose microfibrils.

Exploiting plant transcriptomic databases: Resources, tools, and approaches

There are now more than 300 000 RNA sequencing samples available, stemming from thousands of experiments capturing gene expression in organs, tissues, developmental stages, and experimental treatments for hundreds of plant species. The expression data have great value, as they can be re-analyzed by others to ask and answer questions that go beyond the aims of the study that generated the data. Because gene expression provides essential clues to where and when a gene is active, the data provide powerful tools for predicting gene function, and comparative analyses allow us to study plant evolution from a new perspective. This review describes how we can gain new knowledge from gene expression profiles, expression specificities, co-expression networks, differential gene expression, and experiment correlation. We also introduce and demonstrate databases that provide user-friendly access to these tools.

Genomic Architecture and Evolution of the Cellulose synthase Gene Superfamily as Revealed by Phylogenomic Analysis

The Cellulose synthase superfamily synthesizes cellulose and different hemicellulosic polysaccharides in plant cell walls. While much has been discovered about the evolution and function of these genes, their genomic architecture and relationship with gene (sub-)functionalization and evolution remains unclear. By using 242 genomes covering plant evolution from green algae to eudicots, we performed a large-scale analysis of synteny, phylogenetic, and functional data of the CesA superfamily. Results revealed considerable gene copy number variation across species and gene families, and also two patterns - singletons vs. tandem arrays - in chromosomic gene arrangement. Synteny analysis revealed exceptional conservation of gene architecture across species, but also lineage-specific patterns across gene (sub-)families. Synteny patterns correlated with gene sub-functionalization into primary and secondary CesAs and distinct CslD functional isoforms. Furthermore, a genomic context shift of a group of cotton secondary CesAs was associated with peculiar properties of cotton fiber synthesis. Finally, phylogenetics suggested that primary CesA sequences appeared before the secondary CesAs, while phylogenomic analyses unveiled the genomic trace of the CslD duplication that initiated the CslF family. Our results describe in detail the genomic architecture of the CesA superfamily in plants, highlighting its crucial relevance for gene diversification and sub-functionalization, and for understanding their evolution.

Dynamic roles and intricate mechanisms of ethylene in epidermal hair development in Arabidopsis and cotton

Ethylene affects many aspects of plant growth and development, including root hairs and trichomes growth in Arabidopsis, as well as fiber development in cotton, though the underlying mechanism is unclear. In this article, we update the research progress associated with the main genes in ethylene biosynthesis and signaling pathway, and we propose a clear ethylene pathway based on genome-wide identification of homologues in cotton. Expression pattern analysis using transcriptome data revealed that some candidate genes may contribute to cotton fiber development through the ethylene pathway. Moreover, we systematically summarized the effects of ethylene on the development of epidermal hair and the underlying regulatory mechanisms in Arabidopsis. Based on the knowledge of ethylene-promoted cell differentiation, elongation, and development in different tissues or plants, we advised a possible regulatory network for cotton fiber development with ethylene as the hub. Importantly, we emphasized the roles of ethylene as an important node in regulating cotton vegetative growth, and stress resistance, and suggested utilizing multiple methods to subtly modify ethylene synthesis or signaling in a tissue or spatiotemporal-specific manner to clarify its exact effect on architecture, adaptability of the plant, and fiber development, paving the way for basic research and genetic improvement of the cotton crop.

Cellulose synthase-like protein OsCSLD4 plays an important role in the response of rice to salt stress by mediating abscisic acid biosynthesis to regulate osmotic stress tolerance

Cell wall polysaccharide biosynthesis enzymes play important roles in plant growth, development and stress responses. The functions of cell wall polysaccharide synthesis enzymes in plant growth and development have been well studied. In contrast, their roles in plant responses to environmental stress are poorly understood. Previous studies have demonstrated that the rice cell wall cellulose synthase-like D4 protein (OsCSLD4) is involved in cell wall polysaccharide synthesis and is important for rice growth and development. This study demonstrated that the OsCSLD4 function-disrupted mutant nd1 was sensitive to salt stress, but insensitive to abscisic acid (ABA). The expression of some ABA synthesis and response genes was repressed in nd1 under both normal and salt stress conditions. Exogenous ABA can restore nd1-impaired salt stress tolerance. Moreover, overexpression of OsCSLD4 can enhance rice ABA synthesis gene expression, increase ABA content and improve rice salt tolerance, thus implying that OsCSLD4-regulated rice salt stress tolerance is mediated by ABA synthesis. Additionally, nd1 decreased rice tolerance to osmotic stress, but not ion toxic tolerance. The results from the transcriptome analysis showed that more osmotic stress-responsive genes were impaired in nd1 than salt stress-responsive genes, thus indicating that OsCSLD4 is involved in rice salt stress response through an ABA-induced osmotic response pathway. Intriguingly, the disruption of OsCSLD4 function decreased grain width and weight, while overexpression of OsCSLD4 increased grain width and weight. Taken together, this study demonstrates a novel plant salt stress adaptation mechanism by which crops can coordinate salt stress tolerance and yield.

A novel E6-like gene, E6-2, affects fruit ripening in tomato

Tomato fruit ripening is a complicated and well-coordinated process with numerous metabolic changes resulted from endogenous hormone and genetic regulators. Although the regulation of MADS-box transcription factor (MADS-RIN) controlling fruit ripening has been widely reported, its mechanisms underlying need to be further improved. Here, we characterized a novel tomato E6-like gene, E6-2, whose transcripts showed a high accumulation in fruit ripening stages (Breaker, Breaker+4 and Breaker+7), but a low level was observed in Never ripe (Nr) and ripening inhibitor (rin) mutants. MADS-RIN directly activates the expression of E6-2 in vivo. Additionally, a remarkable reduction of E6-2 was observed in wild-type (WT) tomato fruits at the MG stage treated with 1-MCP. RNAi-mediated silencing of E6-2 resulted in delayed fruit ripening, reduced accumulation of the total carotenoid and lycopene, reduced content of ethylene production, and increased contents of the total pectin, cellulose, starch and soluble sugar. Moreover, the expression of carotenoid biosynthesis genes (PSY1, PDS and ZDS), ripening-related genes (CNR, PG and ERF4), ethylene biosynthesis genes (ACS2, ACO1 and ACO3), ethylene-responsive genes (E4 and E8) and cell wall metabolism genes (TBG4, PL, EXP1 and XTH5) were inhibited in E6-2 -RNAi lines. These results indicate that E6-2 plays an important role in regulating tomato fruit ripening targeted by RIN.

Two Expansin Genes, AtEXPA4 and AtEXPB5, Are Redundantly Required for Pollen Tube Growth and AtEXPA4 Is Involved in Primary Root Elongation in Arabidopsis thaliana

The growth of plant cells is inseparable from relaxation and expansion of cell walls. Expansins are a class of cell wall binding proteins, which play important roles in the relaxation of cell walls. Although there are many members in expansin gene family, the functions of most expansin genes in plant growth and development are still poorly understood. In this study, the functions of two expansin genes, AtEXPA4 and AtEXPB5 were characterized in Arabidopsis thaliana. AtEXPA4 and AtEXPB5 displayed consistent expression patterns in mature pollen grains and pollen tubes, but AtEXPA4 also showed a high expression level in primary roots. Two single mutants, atexpa4 and atexpb5, showed normal reproductive development, whereas atexpa4atexpb5 double mutant was defective in pollen tube growth. Moreover, AtEXPA4 overexpression enhanced primary root elongation, on the contrary, knocking out AtEXPA4 made the growth of primary root slower. Our results indicated that AtEXPA4 and AtEXPB5 were redundantly involved in pollen tube growth and AtEXPA4 was required for primary root elongation.

Genome-Wide Identification of Banana Csl Gene Family and Their Different Responses to Low Temperature between Chilling-Sensitive and Tolerant Cultivars

The cell wall plays an important role in responses to various stresses. The cellulose synthase-like gene (Csl) family has been reported to be involved in the biosynthesis of the hemicellulose backbone. However, little information is available on their involvement in plant tolerance to low-temperature (LT) stress. In this study, a total of 42 Csls were identified in Musa acuminata and clustered into six subfamilies (CslA, CslC, CslD, CslE, CslG, and CslH) according to phylogenetic relationships. The genomic features of MaCsl genes were characterized to identify gene structures, conserved motifs and the distribution among chromosomes. A phylogenetic tree was constructed to show the diversity in these genes. Different changes in hemicellulose content between chilling-tolerant and chilling-sensitive banana cultivars under LT were observed, suggesting that certain types of hemicellulose are involved in LT stress tolerance in banana. Thus, the expression patterns of MaCsl genes in both cultivars after LT treatment were investigated by RNA sequencing (RNA-Seq) technique followed by quantitative real-time PCR (qPCR) validation. The results indicated that MaCslA4/12, MaCslD4 and MaCslE2 are promising candidates determining the chilling tolerance of banana. Our results provide the first genome-wide characterization of the MaCsls in banana, and open the door for further functional studies.

The TaCslA12 gene expressed in the wheat grain endosperm synthesizes wheat-like mannan when expressed in yeast and Arabidopsis

Mannan is a class of cell wall polysaccharides widespread in the plant kingdom. Mannan structure and properties vary according to species and organ. The cell walls of cereal grains have been extensively studied due to their role in cereal processing and to their beneficial effect on human health as dietary fiber. Recently, we showed that mannan in wheat (Triticum aestivum) grain endosperm has a linear structure of β-1,4-linked mannose residues. The aim of this work was to study the biosynthesis and function of wheat grain mannan. We showed that mannan is deposited in the endosperm early during grain development, and we identified candidate mannan biosynthetic genes expressed in the endosperm. The functional study in wheat was unsuccessful therefore our best candidate genes were expressed in heterologous systems. The endosperm-specificTaCslA12 gene expressed in Pichia pastoris and in an Arabidopsis thaliana mutant depleted in glucomannan led to the production of wheat-like linear mannan lacking glucose residues and with moderate acetylation. Therefore, this gene encodes a mannan synthase and is likely responsible for the synthesis of wheat endosperm mannan.

A novel rice fragile culm 24 mutant encodes a UDP-glucose epimerase that affects cell wall properties and photosynthesis

UDP-glucose epimerases (UGEs) are essential enzymes for catalysing the conversion of UDP-glucose (UDP-Glc) into UDP-galactose (UDP-Gal). Although UDP-Gal has been well studied as the substrate for the biosynthesis of carbohydrates, glycolipids, and glycoproteins, much remains unknown about the biological function of UGEs in plants. In this study, we selected a novel rice fragile culm 24 (Osfc24) mutant and identified it as a nonsense mutation of the FC24/OsUGE2 gene. The Osfc24 mutant shows a brittleness phenotype with significantly altered cell wall composition and disrupted orientation of the cellulose microfibrils. We found significantly reduced accumulation of arabinogalactan proteins in the cell walls of the mutant, which may consequently affect plant growth and cell wall deposition, and be responsible for the altered cellulose microfibril orientation. The mutant exhibits dwarfism and paler leaves with significantly decreased contents of galactolipids and chlorophyll, resulting in defects in plant photosynthesis. Based on our results, we propose a model for how OsUGE2 participates in two distinct metabolic pathways to co-modulate cellulose biosynthesis and cell wall assembly by dynamically providing UDP-Gal and UDP-Glc substrates.

Cotton CSLD3 restores cell elongation and cell wall integrity mainly by enhancing primary cellulose production in the Arabidopsis cesa6 mutant

Overexpression of cotton cellulose synthase like D3 (GhCSLD3) gene partially rescued growth defect of atcesa6 mutant with restored cell elongation and cell wall integrity mainly by enhancing primary cellulose production. Among cellulose synthase like (CSL) family proteins, CSLDs share the highest sequence similarity to cellulose synthase (CESA) proteins. Although CSLD proteins have been implicated to participate in the synthesis of carbohydrate-based polymers (cellulose, pectins and hemicelluloses), and therefore plant cell wall formation, the exact biochemical function of CSLD proteins remains controversial and the function of the remaining CSLD genes in other species have not been determined. In this study, we attempted to illustrate the function of CSLD proteins by overexpressing Arabidopsis AtCSLD2, -3, -5 and cotton GhCSLD3 genes in the atcesa6 mutant, which has a background that is defective for primary cell wall cellulose synthesis in Arabidopsis. We found that GhCSLD3 overexpression partially rescued the growth defect of the atcesa6 mutant during early vegetative growth. Despite the atceas6 mutant having significantly reduced cellulose contents, the defected cell walls and lower dry mass, GhCSLD3 overexpression largely restored cell wall integrity (CWI) and improved the biomass yield. Our result suggests that overexpression of the GhCSLD protein enhances primary cell wall synthesis and compensates for the loss of CESAs, which is required for cellulose production, therefore rescuing defects in cell elongation and CWI.

Nitrogen Starvation Differentially Influences Transcriptional and Uptake Rate Profiles in Roots of Two Maize Inbred Lines with Different NUE

Nitrogen use efficiency (NUE) of crops is estimated to be less than 50%, with a strong impact on environment and economy. Genotype-dependent ability to cope with N shortage has been only partially explored in maize and, in this context, the comparison of molecular responses of lines with different NUE is of particular interest in order to dissect the key elements underlying NUE. Changes in root transcriptome and NH₄⁺/NO₃^- uptake rates during growth (after 1 and 4 days) without N were studied in high (Lo5) and low (T250) NUE maize inbred lines. Results suggests that only a small set of transcripts were commonly modulated in both lines in response to N starvation. However, in both lines, transcripts linked to anthocyanin biosynthesis and lateral root formation were positively affected. On the contrary, those involved in root elongation were downregulated. The main differences between the two lines reside in the ability to modulate the transcripts involved in the transport, distribution and assimilation of mineral nutrients. With regard to N mineral forms, only the Lo5 line responded to N starvation by increasing the NH₄⁺ fluxes as supported by the upregulation of a transcript putatively involved in its transport.

A Pivotal Role of Hormones in Regulating Cotton Fiber Development

Cotton is the main source of renewable fiber in the world and is primarily used for textile production. Cotton fibers are single cells differentiated from the ovule epidermis and are an excellent model system for studying cell elongation, polyploidization, and cell wall biosynthesis. Plant hormones, which are present in relatively low concentrations, play important roles in various developmental processes, and recently, multiple reports have revealed the pivotal roles of hormones in regulating cotton fiber development. For example, exogenous application of hormones has been shown to promote the initiation and growth of fiber cells. However, a comprehensive understanding about phytohormone regulating fiber development is still unknown. Here, we focus on recent advances in elucidating the roles of multiple phytohormones in the control of fiber development, namely auxin, gibberellin, brassinosteroid, ethylene, cytokinin, abscisic acid, and strigolactones. We not only review the identification of genes involved in hormone biosynthetic and signaling pathways but also discuss the mechanisms of these phytohormones in regulating the initiation and elongation of fiber cells in cotton. Auxin, gibberellin, brassinosteroid, ethylene, jasmonic acid, and strigolactones play positive roles in fiber development, whereas cytokinin and abscisic acid inhibit fiber growth. Our aim is to provide a comprehensive review of the role of phytohormones in cotton fiber development that will serve as the basis for further elucidation of the mechanisms by which plant hormones regulate fiber growth.