Xyloglucan Endotransglycosylase/hydrolase Research Articles

Functional Analysis of Cucumis melo CmXTH11 in Regulating Drought Stress Tolerance in Arabidopsis thaliana

The CmXTH11 gene, a member of the XTH (xyloglucan endotransglycosylase/hydrolase) family, plays a crucial role in plant responses to environmental stress. In this study, we heterologously expressed the melon gene CmXTH11 in Arabidopsis to generate overexpressing transgenic lines, thereby elucidating the regulatory role of CmXTH11 in water stress tolerance. Using these lines of CmXTH11 (OE1 and OE2) and wild-type (WT) Arabidopsis as experimental materials, we applied water stress treatments (including osmotic stress and soil drought) and rewatering treatments to investigate the response mechanisms of melon CmXTH11 in Arabidopsis under drought stress from a physiological and biochemical perspective. Overexpression of CmXTH11 significantly improved root growth under water stress conditions. The OE lines exhibited longer roots and a higher number of lateral roots compared to WT plants. The enhanced root system contributed to better water uptake and retention. Under osmotic and drought stress, the OE lines showed improved survival rates and less wilting compared to WT plants. Biochemical analyses revealed that CmXTH11 overexpression led to lower levels of malondialdehyde (MDA) and reduced electrolyte leakage, indicating decreased oxidative damage. The activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), were significantly higher in OE lines, suggesting enhanced oxidative stress tolerance. The CmXTH11 gene positively regulates water stress tolerance in Arabidopsis by enhancing root growth, improving water uptake, and reducing oxidative damage. Overexpression of CmXTH11 increases the activities of antioxidant enzymes, thereby mitigating oxidative stress and maintaining cellular integrity under water deficit conditions. These findings suggest that CmXTH11 is a potential candidate for genetic improvement of drought resistance in crops.

Site-directed mutagenesis and molecular docking simulations identified the crucial substrate binding site asparagine 101 of xyloglucan endotransglycosylase/hydrolase (XTH) in woody plants

Xyloglucan endotransglycosylase/hydrolase (XTH) is a key enzyme in plant cell wall remodeling. Previous investigations on the angiosperm Populus tomentosa identified 11 PtoXTH proteins with the XTH catalytic motif. Surprisingly, only two (PtoXTH27 and PtoXTH34) exhibited xyloglucan endotransglucosylase (XET) activity, suggesting the presence of additional key substrate binding or catalytic activity sites within XTH proteins. To test this hypothesis, we performed site-directed mutagenesis on selected amino acids in PtoXTH27 and PtoXTH34 and characterized their biochemical properties. Molecular docking simulations and biochemical analyses revealed that N101 is a critical substrate binding site, while Q80, M81, and V180 are essential functional residues influencing XET activity in XTH proteins. Notably, XET-deficient PtoXTH26 regained activity following site-directed mutation, underscoring the significance of these residues. Expanding our study to the gymnosperm Larix kaempferi, we identified two XTH proteins: LkXTH1, which exhibited both the key substrate binding site and XET activity, and LkXTH2, which lacked XET activity. Intriguingly, LkXTH2 regained XET activity after site-directed mutation, highlighting the versatility of the newly identified substrate binding site across different woody plants subphyla. This research provides a theoretical basis for the rapid identification of enzymatically active members within the XTH gene family in woody plants. Furthermore, our findings offer insights into the targeted engineering of XTH enzymes, paving the way for advancements in plant biotechnology and crop improvement.

Populus endo-glucanase 16 localizes to the cell walls of developing tissues.

The hemicelluloses comprise a group of matrix glycans that interact with cellulose microfibrils in plant cell walls and play important roles in establishing wall architecture. The structures of hemicelluloses are determined by carbohydrate-active enzymes (CAZymes) that synthesize, integrate, and break down these polymers. Specifically, endo-glucanase 16 (EG16) enzymes, which are related to the well-known xyloglucan endotransglycosylase/hydrolase (XTH) gene products in Glycoside Hydrolase Family 16 (GH16), have been implicated in the degradation of the β(1,4)-linked backbone of mixed-linkage β(1,3);β(1,4)-glucans (MLG) and xyloglucans. EG16 members are single-copy genes found in most plant clades but are absent from many eudicots, including the model plant Arabidopsis thaliana. Until recently, EG16 members had only been characterized in vitro, establishing their substrate specificity, protein structure, and phylogenetic history, but their biological function was unknown. Here we used a hybrid polar, Populus alba× Populus grandidentata (P39), as a model to examine EG16 expression, subcellular localization, and pheno- and chemotypes of EG16-downregulated P39 plants. Populus EG16 expression is strong in young tissues, but RNAi-mediated downregulation did not impact plant growth nor the fine structure of the hemicellulose xyloglucan, suggesting a restricted or currently unknown role in angiosperm physiology.

Brassinosteroid Biosynthetic Gene CmDWF4 Regulates Bud Outgrowth in Chrysanthemum morifolium

Brassinosteroids (BRs), a class of steroid phytohormones, play a critical role in plant growth and development. The <i>DWF4</i> gene encodes a cytochrome P450 enzyme (CYP90B1), which is considered a rate-limiting enzyme in BR biosynthesis. Here, we identified a homologous gene of <i>DWF4</i> in chrysanthemum, <i>CmDWF4</i>. This gene was predicted to encode 491 amino acid residues with a molecular weight of 56.2 kDa and an isoelectric point (pI) of 9.10. Overexpression of <i>CmDWF4</i> in chrysanthemum was found to significantly increase growth rate, number, and length of lateral buds. Transcriptome analysis showed that multiple xyloglucan endotransglycosylase/hydrolase (XTH) family encoding genes associated with cell wall modification were up-regulated in <i>CmDWF4</i>-overexpressing lines. qRT-PCR assay confirmed the up-regulation of <i>CmXTH6</i>, <i>CmXTH23</i>, and <i>CmXTH28</i> in <i>CmDWF4</i>-overexpression line. Overall, this work establishes a mechanism by which BR biosynthetic gene <i>CmDWF4</i> promotes lateral bud outgrowth in chrysanthemum, possibly through regulating cell elongation and expansion.

Identification of the Xyloglucan Endotransglycosylase/Hydrolase (XTH) Gene Family Members Expressed in Boehmeria nivea in Response to Cadmium Stress.

Xyloglucan endotransglycosylase/hydrolase (XTH) genes play an important role in plant resistance to abiotic stress. However, systematic studies of the response of Boehmeria nivea (ramie) XTH genes (BnXTHs) to cadmium (Cd) stress are lacking. We sought to identify the BnXTH-family genes in ramie through bioinformatics analyses and to investigate their responses to Cd stress. We identified 19 members of the BnXTH gene family from the ramie genome, referred to as BnXTH1-19, among which BnXTH18 and BnXTH19 were located on no chromosomes and the remaining genes were unevenly distributed across 11 chromosomes. The 19 members were divided into four groups, Groups I/II/IIIA/IIIB, according to their phylogenetic relationships, and these groups were supported by analyses of intron-exon structure and conserved motif composition. A highly conserved catalytic site (HDEIDFEFLG) was observed in all BnXTH proteins. Additionally, three gene pairs (BnXTH6-BnXTH16, BnXTH8-BnXTH9, and BnXTH17-BnXTH18) were obtained with a fragment and tandem-repeat event analysis of the ramie genome. An analysis of cisregulatory elements revealed that BnXTH expression might be regulated by multiple hormones and abiotic and biotic stress responses. In particular, 17 cisregulatory elements related to abiotic and biotic stress responses and 11 cisregulatory elements related to hormone responses were identified. We also found that most BnXTH genes responded to Cd stress, and BnXTH1, BnXTH3, BnXTH6, and BnXTH15 were most likely to contribute to the Cd tolerance of ramie, as evidenced by the substantial increases in expression under Cd treatment. Heterologous expression of BnXTH1, BnXTH6, and BnXTH15 significantly enhanced the Cd tolerance of transgenic yeast cells. These results suggest that the BnXTH gene family is involved in Cd stress responses, laying a theoretical foundation for functional studies of BnXTH genes and the innovative breeding of Cd-tolerant ramie.

Cytological, physiological and transcriptomic analysis of variegated Leaves in Primulina pungentisepala offspring

BackgroundPrimulina pungentisepala is suitable for use as a potted plant because of its beautiful leaf variegation, which is significantly different in its selfed offspring. However, the mechanism of P. pungentisepala leaf variegation is unclear. In this study, two types of offspring showing the greatest differences were compared in terms of leaf structure, chlorophyll contents, chlorophyll fluorescence parameters and transcriptomes to provide a reference for studying the molecular mechanism of structural leaf variegation.ResultsAir spaces were found between water storage tissue, and the palisade tissue cells were spherical in the white type. The content of chlorophyll a and total chlorophyll (chlorophyll a + b) was significantly lower in the white type, but there were no significant differences in the content of chlorophyll b, chlorophyll a/b or chlorophyll fluorescence parameters between the white and green types. We performed transcriptomic sequencing to identify differentially expressed genes (DEGs) involved in cell division and differentiation, chlorophyll metabolism and photosynthesis. Among these genes, the expression of the cell division- and differentiation-related leucine-rich repeat receptor-like kinases (LRR-RLKs), xyloglucan endotransglycosylase/hydrolase (XET/H), pectinesterase (PE), expansin (EXP), cellulose synthase-like (CSL), VARIEGATED 3 (VAR3), and ZAT10 genes were downregulated in the white type, which might have promoted the development air spaces and variant palisade cells. Chlorophyll biosynthesis-related hydroxymethylbilane synthase (HEMC) and the H subunit of magnesium chelatase (CHLH) were downregulated, while chlorophyll degradation-related chlorophyllase-2 (CHL2) was upregulated in the white type, which might have led to lower chlorophyll accumulation.ConclusionLeaf variegation in P. pungentisepala was caused by a combination of mechanisms involving structural variegation and low chlorophyll levels. Our research provides significant insights into the molecular mechanisms of structural leaf variegation.

Root cell wall remodeling mediates copper oxide nanoparticles phytotoxicity on lettuce (Lactuca sativa L.)

Root cell wall (RCW) remodeling induced by copper oxide nanoparticles (CuO NPs) and its consequences for root growth of lettuce (Lactuca sativa L.) were investigated in this study. The results showed that a low concentration of CuO NPs (5 mg L−1) stimulated reactive oxygen species (ROS) signaling, led to the degradation of pectin by H2O2, and promoted root elongation by 22.1% by triggering RCW loosening. However, under treatment with a high concentration of CuO NPs (450 mg L−1), the unordered distribution of pectin homogalacturonan enhanced cell wall adhesion. Also, the increased xyloglucan and the decreased xyloglucan endotransglycosylase/hydrolase (XTH) activities caused cell wall stiffening, making it difficult for lettuce roots to extend. Meanwhile, the contents of hemicellulose and low-methylated pectin were increased remarkably due to the downregulation of the encoding genes XTH15, XTH17, XTH31 and the upregulation of PME3, which provided abundant binding sites of RCW with CuO NPs. In addition, the accelerated development of the apoplastic barrier and root lignification blocked the absorption of CuO NPs, and the endodermal cell walls were doubled in thickness, greatly enhancing their retention capacity to CuO NPs. Taken together, the above findings suggest that CuO NPs have concentration-dependent effects on lettuce roots, which are associated with plant tolerance and mediated by RCW remodeling.

Physcomitrium (Physcomitrella) patens endo-glucanase 16 is involved in the cell wall development of young tissue.

Plants maintain large repertoires of carbohydrate-active enzymes (CAZymes)-comprising between 3% and 10% of their genomes-to synthesize, modify, and degrade the polysaccharide components of the cell wall. We recently identified a unique group of plant endo-glucanases from Glycoside Hydrolase Family 16, viz. EG16 orthologs, which constitute a sister clade to the well-known XYLOGLUCAN ENDO-TRANSGLYCOSYLASE/HYDROLASE (XTH) gene products. Biochemical analysis of EG16 orthologs from poplar (Populus trichocarpa), grapevine (Vitis vinifera), and spreading earthmoss (Physcomitrium patens) has demonstrated that these endo-glucanases are distinctly active on cell wall matrix glycans, mixed-linkage β(1,3);β(1,4)-glucan and xyloglucan (XyG), and that enzyme structure and specificity is highly conserved across diverse plant lineages. However, the physiological role of EG16 orthologs in any species is presently unknown. To shed light on EG16 function in vivo, here we performed reverse genetics and protein localization analyses of the single EG16 ortholog in the model moss P. patens, where this gene is highly expressed in young, expanding tissues, particularly in protonema. Surprisingly, deletion of the PpEG16 gene by homologous recombination led to an increase in growth, as well as accelerated senescence. Notably, the PpEG16 protein was shown to co-localize with XyG in the cell wall of protonema tissue, specifically at cell tips, despite lacking a secretion signal peptide. Although the precise biological role of EG16 orthologs remains elusive, our results implicate these highly conserved glycoside hydrolases in cell wall polysaccharide remodeling and recycling. We anticipate that these foundational results will inform future studies on EG16 function across plant lineages.

In silico analysis of XTH gene family from barley (Hordeum vulgare L.) and their comparative expression analysis during germination

Changes in plant cell walls are critical for expansion and growth. Xyloglucan endotransglycosylase/hydrolase (XTH) enzymes are the major modifiers of xyloglucan within the cell wall and are present as large gene families. Despite the paucity of xyloglucan in barley, our analyses of the barley genome revealed at least 42 XTH genes, the most XTH members recorded for a monocot genome to date. In this paper, we show a detailed look at the barley XTH gene family, including detailed bioinformatics analyses of conserved protein motifs and structure, phylogenetic relationships, and a comparison of the expression patterns during germination and seedling growth using RT-qPCR and RNA-Seq analyses. Overall, there was a good correlation between RT-qPCR and RNA-Seq data for similar tissues. RNA-Seq data showed many different expression profile patterns, from broad, high level expression for some XTH genes to highly tissue specific patterns for others. RT-qPCR expression patterns also varied widely between genes. The highest expressing gene, HvXET4, had levels around five times that of the highest control gene tubulin. Given the low levels of xyloglucan found in barley, this high level of expression suggests that the enzyme may be catalysing reactions with other cell wall polysaccharides. We propose roles for many of the HvXTH genes based on the results shown here.

Transcriptome-wide characterization and functional analysis of Xyloglucan endo-transglycosylase/hydrolase (XTH) gene family of Salicornia europaea L. under salinity and drought stress

BackgroundSalicornia europaea is a halophyte that has a very pronounced salt tolerance. As a cell wall manipulating enzyme, xyloglucan endotransglycosylase/hydrolase (XTH) plays an important role in plant resistance to abiotic stress. However, no systematic study of the XTH gene family in S. europaea is well known. PacBio Iso-Seq transcriptome sequence data were used for bioinformatics and gene expression analysis using real-time quantitative polymerase chain reaction (RT-qPCR).ResultsTranscriptome sequencing (PacBio Iso-Seq system) generated 16,465,671 sub-reads and after quality control of Iso-Seq, 29,520 isoforms were obtained with an average length of 2112 bp. A total of 24,869 unigenes, with 98% of which were obtained using coding sequences (CDSs), and 6398 possible transcription factors (TFs) were identified. Thirty-five (35) non-redundant potential SeXTH proteins were identified in S. europaea and categorized into group I/II and group III based on their genetic relatedness. Prediction of the conserved motif revealed that the DE(I/L/F/V)DF(I)EFLG domain was conserved in the S. europaea proteins and a potential N-linked glycosylation domain N(T)V(R/L/T/I)T(S/K/R/F/P)G was also located near the catalytic residues. All SeXTH genes exhibited discrete expression patterns in different tissues, at different times, and under different stresses. For example, 27 and 15 SeXTH genes were positively expressed under salt stress in shoots and roots at 200 mM NaCl in 24 h, and 34 SeXTH genes were also positively regulated under 48 h of drought stress in shoots and roots. This indicates their function in adaptation to salt and drought stress.ConclusionThe present study discovered SeXTH gene family traits that are potential stress resistance regulators in S. europaea, and this provides a basis for future functional diversity research.

Conservation of endo-glucanase 16 (EG16) activity across highly divergent plant lineages.

Plant cell walls are highly dynamic structures that are composed predominately of polysaccharides. As such, endogenous carbohydrate active enzymes (CAZymes) are central to the synthesis and subsequent modification of plant cells during morphogenesis. The endo-glucanase 16 (EG16) members constitute a distinct group of plant CAZymes, angiosperm orthologs of which were recently shown to have dual β-glucan/xyloglucan hydrolase activity. Molecular phylogeny indicates that EG16 members comprise a sister clade with a deep evolutionary relationship to the widely studied apoplastic xyloglucan endo-transglycosylases/hydrolases (XTH). A cross-genome survey indicated that EG16 members occur as a single ortholog across species and are widespread in early diverging plants, including the non-vascular bryophytes, for which functional data were previously lacking. Remarkably, enzymological characterization of an EG16 ortholog from the model moss Physcomitrella patens (PpEG16) revealed that EG16 activity and sequence/structure are highly conserved across 500 million years of plant evolution, vis-à-vis orthologs from grapevine and poplar. Ex vivo biomechanical assays demonstrated that the application of EG16 gene products caused abrupt breakage of etiolated hypocotyls rather than slow extension, thereby indicating a mode-of-action distinct from endogenous expansins and microbial endo-glucanases. The biochemical data presented here will inform future genomic, genetic, and physiological studies of EG16 enzymes.

Plasma-activated water regulates root hairs and cotyledon size dependent on cell elongation in Nicotiana tabacum L.

Tobacco is an excellent model plant to study developmental processes and cellular biology. Surface dielectric barrier discharge (sDBD) was used to generate plasma activated water (PAW), and the PAW was indirectly applied to study tobacco plant growth during the early developmental stages. Solid media were treated with the PAW for 8- and 18-day-old seedlings, and the effects on both the vegetative and root phenotypes were observed during the early developmental stages. In the vegetative tissue, the cotyledon size was large for the seedling that was cultivated by plasma activated water for the 12 min PAW (PAW12) treatment. The PAW dramatically elongated the cotyledon by 40% due to increased cell expansion in the leaf-length direction, not cell proliferation. In addition to the vegetative tissue, the root length due to the PAW was significantly enhanced at the primary root with elongated root hairs. According to molecular analysis, the NT_ COBRA-LIKE 9 (COBL) and two NT_ XYLOGLUCAN ENDO-TRANSGLYCOSYLASE/HYDROLASE (XTH) genes, NT_XTH9 and NT_XTH15, were significantly over-expressed by the PAW treatment compared with untreated deionized water (DW), indicating that the PAW effects are from modulating the expression of target genes. These results demonstrate that PAW might promote tobacco plant growth both in the cotyledon and root hair tissues via the NT_COBL, NT_XTH9 and NT_XTH15 genes.

Isolation and characterization of Populus xyloglucan endotransglycosylase/hydrolase (XTH) involved in osmotic stress responses

Xyloglucan endotransglycosylase/hydrolase (XTH) belongs to the GH16 subfamily of the glycoside hydrolases of carbohydrate active enzymes and plays an important role in the structure and function of plant cell walls. In this study, 11 members of the XTH gene family were cloned from Populus tomentosa. A bioinformatics analysis revealed that 11 PtoXTHs could be classified into three groups, where PtoXTH27 and PtoXTH34 were most likely to exhibit XTH activity. Biochemical analyses of purified PtoXTHs demonstrated that PtoXTH27 and PtoXTH34 had detectable xyloglucan endotransglucosylase (XET) activity, while the others did not exhibit XET or XEH activity. Moreover, enzymatic assays revealed that the optimum reaction temperature of both PtoXTH27 and PtoXTH34 was 37 °C, while their optimum pH values differed, such that PtoXTH27 was 6.0 and PtoXTH34 was 5.0. Enzyme kinetic parameters indicated that PtoXTH34 had higher affinity for the receptor substrate, XXXG, implying that PtoXTH34 and PtoXTH27 in plants have different substrate structure specificity. Finally, heterologous expression of XTH significantly increased intracellular total sugar content and osmotolerance of yeast cells, indicating that PtoXTH27 and PtoXTH34 are potentially involved in osmotic stress responses. These results clearly demonstrate the enzymatic characteristics and putative role of XTH in osmotic stress responses.

Genome-Wide Identification and Characterization of Xyloglucan Endotransglycosylase/Hydrolase in Ananas comosus during Development.

Xyloglucan endotransglycosylase/hydrolase (XTH) is a cell-wall-modifying enzyme participating in diverse cell morphogenetic processes and adaptation to stress. In this study, 48 XTH genes were identified from two pineapple (Ananas comosus) cultivars (‘F153’ and ‘MD2’) and designated Ac(F153)XTH1 to -24 and Ac(MD2)XTH1 to -24 based on their orthology with Arabidopsis thaliana genes. Endoglucanase family 16 members were identified in addition to XTHs of glycoside hydrolase family 16. Phylogenetic analysis clustered the XTHs into three major groups (Group I/II, III and Ancestral Group) and Group III was subdivided into Group IIIA and Group IIIB. Similar gene structure and motif number were observed within a group. Two highly conserved domains, glycosyl hydrolase family 16 (GH16-XET) and xyloglucan endotransglycosylase C-terminus (C-XET), were detected by multiple sequences alignment of all XTHs. Segmental replication were detected in the two cultivars, with only the paralogous pair Ac(F153)XTH7-Ac(F153)XTH18 presented in ‘F153’ prior to genomic expansion. Transcriptomic analysis indicated that XTHs were involved in the regulation of fruit ripening and crassulacean acid metabolism with tissue specificity and quantitative real-time PCR analysis suggested that Ac(MD2)XTH18 was involved in root growth. The results enhance our understanding of XTHs in the plant kingdom and provide a basis for further studies of functional diversity in A. comosus.

Engineering the acceptor substrate specificity in the xyloglucan endotransglycosylase TmXET6.3 from nasturtium seeds (Tropaeolum majus L.).

The knowledge of substrate specificity of XET enzymes is important for the general understanding of metabolic pathways to challenge the established notion that these enzymes operate uniquely on cellulose-xyloglucan networks. Xyloglucan xyloglucosyl transferases (XETs) (EC 2.4.1.207) play a central role in loosening and re-arranging the cellulose-xyloglucan network, which is assumed to be the primary load-bearing structural component of plant cell walls. The sequence of mature TmXET6.3 from Tropaeolum majus (280 residues) was deduced by the nucleotide sequence analysis of complete cDNA by Rapid Amplification of cDNA Ends, based on tryptic and chymotryptic peptide sequences. Partly purified TmXET6.3, expressed in Pichia occurred in N-glycosylated and unglycosylated forms. The quantification of hetero-transglycosylation activities of TmXET6.3 revealed that (1,3;1,4)-, (1,6)- and (1,4)-β-D-glucooligosaccharides were the preferred acceptor substrates, while (1,4)-β-D-xylooligosaccharides, and arabinoxylo- and glucomanno-oligosaccharides were less preferred. The 3D model of TmXET6.3, and bioinformatics analyses of identified and putative plant xyloglucan endotransglycosylases (XETs)/hydrolases (XEHs) of the GH16 family revealed that H94, A104, Q108, K234 and K237 were the key residues that underpinned the acceptor substrate specificity of TmXET6.3. Compared to the wild-type enzyme, the single Q108R and K237T, and double-K234T/K237T and triple-H94Q/A104D/Q108R variants exhibited enhanced hetero-transglycosylation activities with xyloglucan and (1,4)-β-D-glucooligosaccharides, while those with (1,3;1,4)- and (1,6)-β-D-glucooligosaccharides were suppressed; the incorporation of xyloglucan to (1,4)-β-D-glucooligosaccharides by the H94Q variant was influenced most extensively. Structural and biochemical data of non-specific TmXET6.3 presented here extend the classic XET reaction mechanism by which these enzymes operate in plant cell walls. The evaluations of TmXET6.3 transglycosylation activities and the incidence of investigated residues in other members of the GH16 family suggest that a broad acceptor substrate specificity in plant XET enzymes could be more widespread than previously anticipated.

Characterization of the XTH Gene Family: New Insight to the Roles in Soybean Flooding Tolerance.

Xyloglucan endotransglycosylases/hydrolases (XTHs) are a class of enzymes involved in the construction and remodeling of cellulose/xyloglucan crosslinks and play an important role in regulating cell wall extensibility. However, little is known about this class of enzymes in soybean. Here, 61 soybean XTH genes (GmXTHs) were identified and classified into three subgroups through comparative phylogenetic analysis. Genome duplication greatly contributed to the expansion of GmXTH genes in soybean. A conserved amino acid motif responsible for the catalytic activity was identified in all GmXTHs. Further expression analysis revealed that most GmXTHs exhibited a distinct organ-specific expression pattern, and the expression level of many GmXTH genes was significantly associated with ethylene and flooding stress. To illustrate a possible role of XTH genes in regulating stress responses, the Arabidopsis AtXTH31 gene was overexpressed in soybean. The generated transgenic plants exhibited improved tolerance to flooding stress, with a higher germination rate and longer roots/hypocotyls during the seedling stage and vegetative growth stages. In summary, our combined bioinformatics and gene expression pattern analyses suggest that GmXTH genes play a role in regulating soybean stress responses. The enhanced soybean flooding tolerance resulting from the expression of an Arabidopsis XTH also supports the role of XTH genes in regulating plant flooding stress responses.

Comprehensive cross-genome survey and phylogeny of glycoside hydrolase family 16 members reveals the evolutionary origin of EG16 and XTH proteins in plant lineages.

Carbohydrate-active enzymes (CAZymes) are central to the biosynthesis and modification of the plant cell wall. An ancient clade of bifunctional plant endo-glucanases (EG16 members) was recently revealed and proposed to represent a transitional group uniting plant xyloglucan endo-transglycosylase/hydrolase (XTH) gene products and bacterial mixed-linkage endo-glucanases in the phylogeny of glycoside hydrolase family 16 (GH16). To gain broader insights into the distribution and frequency of EG16 and other GH16 members in plants, the PHYTOZOME, PLAZA, NCBI and 1000 PLANTS databases were mined to build a comprehensive census among 1289 species, spanning the broad phylogenetic diversity of multiple algae through recent plant lineages. EG16, newly identified EG16-2 and XTH members appeared first in the green algae. Extant EG16 members represent the early adoption of the β-jellyroll protein scaffold from a bacterial or early-lineage eukaryotic GH16 gene, which is characterized by loop deletion and extension of the N terminus (in EG16-2 members) or C terminus (in XTH members). Maximum-likelihood phylogenetic analysis of EG16 and EG16-2 sequences are directly concordant with contemporary estimates of plant evolution. The lack of expansion of EG16 members into multi-gene families across green plants may point to a core metabolic role under tight control, in contrast to XTH genes that have undergone the extensive duplications typical of cell-wall CAZymes. The present census will underpin future studies to elucidate the physiological role of EG16 members across plant species, and serve as roadmap for delineating the closely related EG16 and XTH gene products in bioinformatic analyses of emerging genomes and transcriptomes.

Changes in Activities of Key Enzymes in Sugarcane Stem at Different Growing Stages

Sugarcane is the most important sugar crop in China, which mainly focuses on the upper stem of the harvested land. The proper regulation of the proportion of internode elongation is the key to determine the yield and sugar. Therefore, it is of great significance to study the mechanism of the dynamic change of elongation between cane joints in order to improve the yield of sugar cane and sucrose. To investigate the biochemical mechanism of stem elongation in sugarcane, stem samples were collected at the pre-elongation stage (9-10 leaves) (Ls1), early elongation stage (12-13 leaves) (Ls2) and rapid elongation stage (15-16 leaves) (Ls3). The change trends in the activities of NAD kinase (NADK), calcium-dependent protein kinase (CDPKs), α-mannosidase, α-galactosidase, β-glucosidase, cellulase, xyloglucan endo-transglycosylase/hydrolase (XTH) and catalase (CAT) were completely consistent, showing rapid elongation stage > early elongation stage > pre-elongation stage, while the activities of β-glucosidase, peroxidase (POD) and α-glucosidase were in opposite, and the activities of calmodulin and β-mannosidase showed the same single-peak trend, and the peak was at early elongation stage. The enzyme activities of β-galactosidase and pectinase did not show significant difference at different stages. The results indicate that the elongation of internodes was closely related to the complex physiological metabolism of sugarcane, and the key enzymes play roles at different time but β-galactosidase and pectinase have little effect on internodes elongation in sugarcane.

XTHs from Fragaria vesca: genomic structure and transcriptomic analysis in ripening fruit and other tissues

BackgroundFragaria vesca or ‘woodland strawberry’ has emerged as an attractive model for the study of ripening of non-climacteric fruit. It has several advantages, such as its small genome and its diploidy. The recent availability of the complete sequence of its genome opens the possibility for further analysis and its use as a reference species. Fruit softening is a physiological event and involves many biochemical changes that take place at the final stages of fruit development; among them, the remodeling of cell walls by the action of a set of enzymes. Xyloglucan endotransglycosylase/hydrolase (XTH) is a cell wall-associated enzyme, which is encoded by a multigene family. Its action modifies the structure of xyloglucans, a diverse group of polysaccharides that crosslink with cellulose microfibrills, affecting therefore the functional structure of the cell wall. The aim of this work is to identify the XTH-encoding genes present in F. vesca and to determine its transcription level in ripening fruit.ResultsThe search resulted in identification of 26 XTH-encoding genes named as FvXTHs. Genetic structure and phylogenetic analyses were performed allowing the classification of FvXTH genes into three phylogenetic groups: 17 in group I/II, 2 in group IIIA and 4 in group IIIB. Two sequences were included into the ancestral group. Through a comparative analysis, characteristic structural protein domains were found in FvXTH protein sequences. In complement, expression analyses of FvXTHs by qPCR were performed in fruit at different developmental and ripening stages, as well as, in other tissues. The results showed a diverse expression pattern of FvXTHs in several tissues, although most of them are highly expressed in roots. Their expression patterns are not related to their respective phylogenetic groups. In addition, most FvXTHs are expressed in ripe fruit, and interestingly, some of them (FvXTH 18 and 20, belonging to phylogenic group I/II, and FvXTH 25 and 26 to group IIIB) display an increasing expression pattern as the fruit ripens.ConclusionA discrete group of FvXTHs (18, 20, 25 and 26) increases their expression during softening of F. vesca fruit, and could take part in cell wall remodeling required for softening in collaboration with other cell wall degrading enzymes.

Interaction between calcium and potassium modulates elongation rate in cotton fiber cells

Calcium (Ca2+) is necessary for fiber cell development in cotton (Gossypium hirsutum), both as a cell wall structural component and for environmental signaling responses. It is also known that potassium (K+) plays a critical role in cotton fiber cell elongation. However, it is unclear whether Ca2+ integrates its activities with K+ to regulate fiber elongation. Here, we report the novel discovery that Ca2+ deficiency, when integrated with K+ signaling, promotes fiber elongation. Using inductively coupled plasma-mass spectrometry (ICP-MS), we determined dynamic profiles of the ionome in ovules and fibers at different developmental stages, and found that a high accumulation of macro-elements, but not Ca2+, was associated with longer fibers. Using an in vitro ovule culture system, we found that under Ca2+-deficient conditions, sufficient K+ (52 mM) rapidly induced ovule and fiber browning, while reduced K+ (2 or 27 mM) not only suppressed tissue browning but also altered fiber elongation. Reduced K+ also enhanced reactive oxygen species scavenging ability and maintained abscisic acid and jasmonic acid levels, which in turn compensated for Ca2+ deficiency. Ca2+ deficiency combined with reduced K+ (0 mM Ca2+ and 27 mM K+) produced longer fibers in cultured ovules, due to cell wall loosening by phytosulfokine (PSK), expansin (EXP), and xyloglucan endotransglycosylase/hydrolase (XTH), and an increase of the K+ content of fiber cells. Using transgenic cotton, we showed that the CBL-INTERACTING PROTEIN KINASE 6 (GhCIPK6) gene mediates the uptake of K+ under Ca2+-deficient conditions. This study establishes a new link between Ca2+, K+, and fiber elongation.