Xyloglucan Endotransglucosylase/hydrolase Genes Research Articles

A Genome-Wide Identification and Expression Analysis of the Xyloglucan Endotransglucosylase/Hydrolase Gene Family in Melon (Cucumis melo L.)

The xyloglucan endotransglucosylase/hydrolase (XTH) family is an important multigene family in plants that plays a key role in cell wall reconstruction and stress tolerance. However, the specific traits of XTH genes and their expression patterns under different stresses have not been systematically studied in melon. In this study, based on the genomic data of Cucumis melon, 29 XTH genes were identified; most of these genes contain two conserved domains (Glyco_hydro_16 and XET_C domains). Based on neighbor-joining phylogenetic analysis, the CmXTHs were divided into four subfamilies, I/II, IIIA, and IIIB, which are distributed across nine chromosomes of melon. Collinearity analysis showed that the melon XTH genes have an evolutionary history consistent with three species: Arabidopsis, tomato, and cucumber. The promoter regions of the CmXTH genes contain numerous cis-acting elements, which are associated with plant growth, hormonal response, and stress responses. RNA-Seq analysis indicated that CmXTH genes exhibit different expression patterns under drought and salt stress treatments, suggesting that this gene family plays an important role under abiotic stress. This study provides a theoretical basis for further studies on the molecular function of XTH genes in melon.

Genome-wide analysis of XTH gene family in cucumber (Cucumis sativus) against different insecticides to enhance defense mechanism

This study investigates how plants protect themselves, specifically looking at a group of genes called Xyloglucan Endotransglucosylase/Hydrolase (XTH) in cucumber plants. A detailed investigation of CsXTH genes, uncover their evolutionary background, structural motifs, regulatory networks, and functional responsibilities. The investigation utilized various bioinformatics tools and databases to highlight the dynamic interplay between CsXTH genes and abiotic stress responses. The investigation begins with a phylogenetic analysis that reveals the cladding of CsXTH genes into four categories. Further unraveling the conserved motif and domain analyses expose the coordination of xyloglucan modification, highlighting essential motifs and domains shared among these genes. Analyzing cis-regulatory elements helps us understand the complex networks that control the defense mechanisms of cucumber plants. Among these elements, CGTCA-motif and TGACG-motif stand out as key players in interpreting environmental signals and coordinating stress responses. The microRNA Csa-miR169 is becoming a key player in regulating the expression of CsXTH genes, and controlling the biological responses of cucumber plants. Chromosome mapping, Ka/Ks calculations, and protein-protein interaction analysis offer insights into the structural and evolutionary dynamics of CsXTH genes. Additionally, the study explores sub-cellular localization, uncovering the diverse cellular compartments where CsXTH genes are active. Finally, through chrysophanol and physcion, we unveil the adaptable functions of specific CsXTH genes in response to distinct treatments, underscoring their role in orchestrating cucumber's adaptive strategies.

Genome-wide analysis of wheat xyloglucan endotransglucosylase/hydrolase (XTH) gene family revealed TaXTH17 involved in abiotic stress responses

BackgroundEnvironmental stresses, including high salinity and drought, severely diminish wheat yield and quality globally. The xyloglucan endotransglucosylase/hydrolase (XTH) family represents a class of cell wall-modifying enzymes and plays important roles in plants growth, development and stress adaptation. However, systematic analyses of XTH family genes and their functions under salt and drought stresses have not been undertaken in wheat.ResultsIn this study, we identified a total of 135 XTH genes in wheat, which were clustered into three evolutionary groups. These TaXTHs were unevenly distributed on 21 chromosomes of wheat with a majority of TaXTHs located on homelogous groups 2, 3 and 7. Gene duplication analysis revealed that segmental and tandem duplication were the main reasons for the expansion of XTH family in wheat. Interaction network predictions indicated that TaXTHs could interact with multiple proteins, including three kinases, one methyltransferase and one gibberellin-regulated protein. The promoters of the TaXTH genes harbored various cis-acting elements related to stress and hormone responses. RNA-seq data analyses showed that some TaXTH genes were induced by salt and drought stresses. Furthermore, we verified that TaXTH17 was induced by abiotic stresses and phytohormone treatments, and demonstrated that TaXTH17 was localized in the secretory pathway and cell wall. Functional analyses conducted in heterologous expression systems and in wheat established that TaXTH17 plays a negative role in plant resistance to salt and drought.ConclusionsWe identified 135 XTH genes in wheat and conducted comprehensive analyses of their phylogenetic relationships, gene structures, conserved motifs, gene duplication events, chromosome locations, interaction networks, cis-acting elements and gene expression patterns. Furthermore, we provided solid evidence supporting the notion that TaXTH17 plays a negative role in plant resistance to salt and drought stresses. Collectively, our results provide valuable insights into understanding wheat XTHs, particularly their involvement in plant stress responses, and establish a foundation for further functional and mechanistic studies of TaXTHs.

Genome-Wide Analysis of the Xyloglucan Endotransglucosylase/Hydrolase (XTH) Gene Family: Expression Pattern during Magnesium Stress Treatment in the Mulberry Plant (Morus alba L.) Leaves.

Mulberry (Morus alba L.), a significant fruit tree crop, requires magnesium (Mg) for its optimal growth and productivity. Nonetheless, our understanding of the molecular basis underlying magnesium stress tolerance in mulberry plants remains unexplored. In our previous study, we identified several differential candidate genes associated with Mg homeostasis via transcriptome analysis, including the xyloglucan endotransglucosylase/hydrolase (XTH) gene family. The XTH gene family is crucial for plant cell wall reconstruction and stress responses. These genes have been identified and thoroughly investigated in various plant species. However, there is no research pertaining to XTH genes within the M. alba plant. This research systematically examined the M. alba XTH (MaXTH) gene family at the genomic level using a bioinformatic approach. In total, 22 MaXTH genes were discovered and contained the Glyco_hydro_16 and XET_C conserved domains. The MaXTHs were categorized into five distinct groups by their phylogenetic relationships. The gene structure possesses four exons and three introns. Furthermore, the MaXTH gene promoter analysis reveals a plethora of cis-regulatory elements, mainly stress responsiveness, phytohormone responsiveness, and growth and development. GO analysis indicated that MaXTHs encode proteins that exhibit xyloglucan xyloglucosyl transferase and hydrolase activities in addition to cell wall biogenesis as well as xyloglucan and carbohydrate metabolic processes. Moreover, a synteny analysis unveiled an evolutionary relationship between the XTH genes in M. alba and those in three other species: A. thaliana, P. trichocarpa, and Zea mays. Expression profiles from RNA-Seq data displayed distinct expression patterns of XTH genes in M. alba leaf tissue during Mg treatments. Real-time quantitative PCR analysis confirmed the expression of the MaXTH genes in Mg stress response. Overall, this research enhances our understanding of the characteristics of MaXTH gene family members and lays the foundation for future functional genomic study in M. alba.

Genome-wide identification and expression analysis of xyloglucan endotransglucosylase/hydrolase genes family in Salicaceae during grafting

BackgroundPoplar (Populus cathayana)and willow (Salix rehderiana) are important fast-growing trees in China. Grafting plays an important role in improving plant stress resistance and construction of ornamental plants. It is found that willow scions grafted onto poplar rootstocks can form ornamental plants. However, this grafted combination has a low survival rate. Many studies have reported that the xyloglucan endotransglucosylase/hydrolase (XTH) family plays an important role in the healing process of grafts.ResultsA total of 38 PtrXTHs and 32 SpuXTHs were identified in poplar and willow respectively, and were classified into three subfamilies. Tandem duplication was the main reason for the expansion of the PtrXTHs. Grafting treatment and Quantitative real time PCR (RT-qPCR) analysis revealed that five XTH genes differentially expressed between self-grafted and reciprocal grafted combinations. Specifically, the high expression levels of SrXTH16, SrXTH17, SrXTH25, PcXTH22 and PcXTH17 may contribute to the high survival rate of the grafted combination with willow scion and poplar rootstock. Subcellular localization identified that the SrXTH16, SrXTH17, SrXTH25, PcXTH17 and PcXTH22 proteins were located on the cell walls. Transcription factors (NAC, MYB and DOF) may regulate the five XTH genes.ConclusionsThis study provides a new understanding of the roles of PcXTH and SrXTH genes and their roles in grafting. Our results will give some hints to explore the molecular mechanisms of PcXTH and SrXTH genes involved in grafting in the future.

Cloning and Analysis of Xyloglucan Endotransglucosylase/ Hydrolase Gene in Cotton

Xyloglucan endotransglucosylase/Hydrolase (XTH) can loosening cell wall by breaking and re-forming the xyloglucan-cellulose crosslinks. Therefore, XTHs in cotton are related to elongation of cotton fibers. To investigate the relation, two XTH genes were cloned, respectively named as GhXTH1（GenBank:AY189971）and GhXTH2（GenBank:JN968478）.GhXTH1 contained 885 nucleotides, encoding 289 aa. GhXTH2 consisted of 885 nucleotides, encoding 289 aa. GhXTH1 and GhXTH2 contained the conserved motif (DEIDFEFLG) , characteristic of XTH family. Bioinformatic analyses showed that they possessed a transmembrane helice and signal peptide respectively. Phylogenetic analysis suggested that GhXTH1 was orthologous gene to AtXTH6、AtXTH7. GhXTH2 was orthologous gene to AtXTH9. In addition,we analysed the expression of GhXTH1 and GhXTH2, respectively in Gossypium hirsutum and Gossypium barbadense. The results showed that transcript levels were lower during cotton fiber development, and transcript level of GhXTH2 were higher than that of GhXTH1.

Exogenous 6-BA inhibited hypocotyl elongation under darkness in Picea crassifolia Kom revealed by transcriptome profiling.

Hypocotyl elongation is an important process in plant growth and development, and is under hormonal regulatory signaling pathways. In our study, exogenous 6-BA significantly inhibited Picea crassifolia hypocotyl elongation more than ethylene in the dark, indicating the existence of different regulatory strategies in conifers, therefore, the P. crassifolia transcriptome was studied to explore the responsive genes and their regulatory pathways for exogenous N6-benzyladenine (6-BA) inhibition of hypocotyl elongation using RNA-Sequencing approach. We present the first transcriptome assembly of P. crassifolia obtained from 24.38 Gb clean data. With lowly-expressed and short contigs excluded, the assembly contains roughly 130,612 unigenes with an N50 length of 1,278 bp. Differential expression analysis found 3,629 differentially expressed genes (DEGs) and found that the differential expression fold of genes was mainly concentrated between 2 and 8 (1 ≤ log2FoldChange ≤ 3). Functional annotation showed that the GO term with the highest number of enriched genes (83 unigenes) was the shoot system development (GO: 0048367) and the KEGG category, plant hormone signal transduction (ko04075), was enriched 30 unigenes. Further analysis revealed that several cytokinin dehydrogenase genes (PcCTD1, PcCTD3 and PcCTD6) catabolized cytokinins, while xyloglucan endotransglucosylase hydrolase gene (PcXTH31), WALLS ARE THIN 1-like gene (PcWAT1-1) and Small auxin-induced gene (PcSAUR15) were strongly repressed thus synergistically completing the inhibition of hypocotyl elongation in P. crassifolia. Besides, PcbHLH149, PcMYB44 and PcERF14 were predicted to be potential core TFs that may form a multi-layered regulatory network with the above proteins for the regulation of hypocotyl growth.

Genome-wide analysis of the XTH gene family and functional analysis of DlXTH23.5/25 during early longan somatic embryogenesis.

Xyloglucan endotransglucosylase (XET)/hydrolase (XTH) is a cell wall-modifying protein that affects cell expansion and loosening of the cell wall. This study focused on the regulatory mechanism of DlXTH genes during early somatic embryogenesis (SE) and the heat stress response in longan. Mining of the available D. longan genome sequence yielded 25 putative XTH genes. Transcript profiles based on RNA sequencing (RNA-seq) data showed that most of the 17 detected DlXTH genes were highly expressed in the embryogenic callus (EC) (8) and globular embryo (GE) (8), and 13 of them responded significantly to heat stress. The assay for transposase-accessible chromatin sequencing (ATAC-seq) data analysis showed that in terms of chromatin accessibility, 22 of the 25 DlXTH genes were open during early SE, and most of the peak DlXTH genes with transcription differences during early SE were associated with high levels of H3K4me1. The most differentially expressed genes, DlXTH23.5 and DlXTH25, were selected for analysis. According to subcellular localization and quantitative real-time PCR (qRT-PCR) analysis, DlXTH23.5/25, which encode cell membrane-localized proteins, were expressed at the highest level in the GE and significantly responded to heat stress. Dual-luciferase assays and transient transformation showed that the transcription factors (TFs) DlWRKY31, DlERF1, and DlERF5 might bind to the DlXTH23.5/25 promoters to activate gene transcription. Transient overexpression of TFs and DlXTH23.5/25 induced XET activity in Nicotiana benthamiana leaves. Under heat stress in the longan EC, the XET activities and expression levels of TFs and DlXTH23.5/25 were significantly increased, and a high concentration of XET might inhibit longan SE. Thus, the regulatory network composed of DlXTH23.5/25 and its related TFs may regulate early longan SE and participate in the regulatory pathway of longan under heat stress via cell wall repair through the action of XET.

Genome-wide identification of XTH genes in Liriodendron chinense and functional characterization of LcXTH21.

Liriodendron chinense is a relic tree species of the family Magnoliaceae with multiple uses in timber production, landscape decoration, and afforestation. L. chinense often experiences drought stress in arid areas. However, the molecular basis underlying the drought response of L. chinense remains unclear. Many studies have reported that the xyloglucan endotransglucosylase/hydrolase (XTH) family plays an important role in drought stress resistance. Hereby, to explore the drought resistance mechanism of L. chinense, we identify XTH genes on a genome-wide scale in L. chinense. A total of 27 XTH genes were identified in L. chinense, and these genes were classified into three subfamilies. Drought treatment and RT-qPCR analysis revealed that six LcXTH genes significantly responded to drought stress, especially LcXTH21. Hence, we cloned the LcXTH21 gene and overexpressed it in tobacco via gene transfer to analyze its function. The roots of transgenic plants were more developed than those of wild-type plants under different polyethylene glycol (PEG) concentration, and further RT-qPCR analysis showed that LcXTH21 highly expressed in root compared to aboveground organs, indicating that LcXTH21 may play a role in drought resistance through promoting root development. The results of this study provide new insights into the roles of LcXTH genes in the drought stress response. Our findings will also aid future studies of the molecular mechanisms by which LcXTH genes contribute to the drought response.

SHORT-ROOT Controls Cell Elongation in the Etiolated Arabidopsis Hypocotyl.

Transcriptional regulation, a core component of gene regulatory networks, plays a key role in controlling individual organism’s growth and development. To understand how plants modulate cellular processes for growth and development, the identification and characterization of gene regulatory networks are of importance. The SHORT-ROOT (SHR) transcription factor is known for its role in cell divisions in Arabidopsis (Arabidopsis thaliana). However, whether SHR is involved in hypocotyl cell elongation remains unknown. Here, we reveal that SHR controls hypocotyl cell elongation via the transcriptional regulation of XTH18, XTH22, and XTH24, which encode cell wall remodeling enzymes called xyloglucan endotransglucosylase/hydrolases (XTHs). Interestingly, SHR activates transcription of the XTH genes, independently of its partner SCARECROW (SCR), which is different from the known mode of action. In addition, overexpression of the XTH genes can promote cell elongation in the etiolated hypocotyl. Moreover, confinement of SHR protein in the stele still induces cell elongation, despite the aberrant organization in the hypocotyl ground tissue. Therefore, it is likely that SHR-mediated growth is uncoupled from SHR-mediated radial patterning in the etiolated hypocotyl. Our findings also suggest that intertissue communication between stele and endodermis plays a role in coordinating hypocotyl cell elongation of the Arabidopsis seedling. Taken together, our study identifies SHR as a new crucial regulator that is necessary for cell elongation in the etiolated hypocotyl.

Soluble carbohydrate concentration and expression of expansin and xyloglucan endotransglucosylase/hydrolase genes in epidermal and parenchyma cells during lily flower opening

To understand the biochemical mechanism underlying flower opening, the manner of cell expansion, soluble carbohydrate concentration, and expression of expansin and xyloglucan endotransglucosylase/hydrolase (XTH) genes were investigated in the petals of Oriental lily (Lilium ‘Sorbonne’). Microscopic observation revealed that petal growth during flower opening mainly depended on cell expansion, which was accompanied by increases in glucose and fructose concentrations in the petals. The adaxial and abaxial sides of the petals grew at different rates during flower opening with petal reflection. To determine the concentration of soluble carbohydrates and the expression of expansin and XTH genes in adaxial and abaxial epidermal cells and parenchyma cells, these cells were separated using tweezers. We confirmed that these cells could be sufficiently separated. Glucose and fructose concentrations were higher in adaxial epidermal cells than in abaxial epidermal cells at the stage immediately preceding flower opening, but these differences diminished during flower opening. Three expansin genes, LhEXPA1, LhEXPA2, and LhEXPA3, and two XTH genes, LhXTH1 and LhXTH2 were isolated. LhXTH1 transcript levels in the petals markedly increased during flower opening and were higher in adaxial epidermal cells than in other types of cells. Conversely, the levels of the three EXPA transcripts decreased during flower opening and there were slight differences in their levels among different cell types, with a few exceptions. In conclusion, differences in glucose and fructose concentrations between adaxial and abaxial epidermal cells, together with the expression of LhXTH1, may contribute to cell expansion associated with flower opening.

The effect of 24-epibrassinolide on gene expression related to cell walls under boron deficiency and toxicity in the leaves of Arabidopsis thaliana

The changing composition of plant cell walls allows for the continuation of the existing structure under normal conditions and also the protection of physical integrity under altering environmental conditions. In this study, the possible effects of the 24-Epibrassinolide (EBL) hormone under boron (B) deficiency and toxicity conditions on the expression of cell wall-related genes [cellulose synthase (CESA), expansin (EXP), xyloglucan endotransglucosylase/hydrolase (XTH) and pectin methylesterase (PME)] were investigated in the rosette leaves of Arabidopsis thaliana. For this purpose, 0 or 3000 ?M of boric acid (BA) and/or 1 ?M of EBL were applied to the plants which were grown in a hydroponic medium for five and ten weeks. While B-toxicity elevated the mRNA levels of the CESA4 and CESA8 genes in the leaves of the five-week-old plants, B-stress (B-deficiency and -toxicity) caused an increase in the expression of the CESA4, CESA6, and CESA8 genes in the ten-week-old plants. The transcript levels of the EXPA5 gene increased under B-stress in the ten-week-old plants whereas the expression of the EXPA8 gene decreased when compared to the control at two developmental stages. Co-treatment of EBL and B-stress strongly elevated the transcript level of the EXPA5 gene in the ten-week-old plants and the EXPA8 gene at both developmental stages. The EXPA14 and XTH23 genes exhibited distinct expression profiles under B-deficiency and -toxicity in both the five- and ten-week-old plants. The transcript level of the XTH21 gene was upregulated in the leaves of the plants exposed to B-stress. The mRNA level of the PME2 and PME41 genes was generally upregulated in response to B-stress in both the five- and ten-week-old plants. 24-Epibrassinolide alone and in combination with B-stress led to a remarkable increase in the expression of the XTH and PME genes compared to the control. These results demonstrate that cell wall genes generally show a similar pattern of expression at both developmental stages and the EBL hormone induces changes in the expression levels of cell wall-related genes under B-stress.

Magnetic Bead Adsorption Extraction of Xyloglucan Endoglucosidase/Hydrolase Gene and Its Expression Analysis in Land Cotton

The xyloglucan Endotransglucosylase/hydrolase (XTH) genes are proposed to encode enzymes responsible for cleaving and reattaching xyloglucan polymers. Despite prior identification of the XTH gene family in Arabidopsis and rice, the XTH family in upland cotton, a tetraploid plant whose fiber cell is an excellent model for the study of plant cell elongation, is yet uncharacterized. In this study, iron tetroxide based magnetic nanobead (Fe3O4 NPs) was successfully prepared and applied to extract xyloglucan endoglucosidase/hydrolase genes. Analysis of the genes can provide insight into the evolutionary significance and function of the XTH gene family. A total of 41 XTH genes found by searching the phytozomev 10 database were classified into three groups based on their phylogeny and the motifs of individual genes. The 25 and 5 GhXTH genes occurred as clusters resulting from the segmental and tandem duplication. More frequent duplication events in cotton contributed to the expansion of the family. Global microarray analysis of GhXTH gene expression in cotton fibers showed that 18 GhXTH genes could be divided into two clusters and four subclusters based on their expression patterns. Accumulated expression levels were relatively high at the elongation stages of the cotton fibers, suggesting that cotton fiber elongation requires high amounts of the GhXTH protein. The expression profiles of GhXTH3 and GhXTH4 showed by quantitative realtime PCR were similar to those determined by microarray. Additionally, the expression levels of GhXTH3 and GhXTH4 in Gossypium barbadense were higher than those in Gossypium hirsutum at developmental stages, indicating that expression levels of GhXTH3 and GhXTH4 in fibers varied among cultivars differing in fiber length.

Expression Analysis of XTH in Stem Swelling of Stem Mustard and Selection of Reference Genes.

Accurate analysis of gene expression requires selection of appropriate reference genes. In this study, we report analysis of eight candidate reference genes (ACTIN, UBQ, EF-1α, UBC, IF-4α, TUB, PP2A, and HIS), which were screened from the genome and transcriptome data in Brassica juncea. Four statistical analysis softwares geNorm, NormFinder, BestKeeper, and RefFinder were used to test the reliability and stability of gene expression of the reference genes. To further validate the stability of reference genes, the expression levels of two CYCD3 genes (BjuB045330 and BjuA003219) were studied. In addition, all genes in the xyloglucan endotransglucosylase/hydrolase (XTH) family were identified in B. juncea and their patterns at different periods of stem enlargement were analyzed. Results indicated that UBC and TUB genes showed stable levels of expression and are recommended for future research. In addition, XTH genes were involved in regulation of stem enlargement expression. These results provide new insights for future research aiming at exploring important functional genes, their expression patterns and regulatory mechanisms for mustard development.

Higher expression of the strawberry xyloglucan endotransglucosylase/hydrolase genes FvXTH9 and FvXTH6 accelerates fruit ripening.

SummaryFruit softening in Fragaria (strawberry) is proposed to be associated with the modification of cell wall components such as xyloglucan by the action of cell wall‐modifying enzymes. This study focuses on the in vitro and in vivo characterization of two recombinant xyloglucan endotransglucosylase/hydrolases (XTHs) from Fragaria vesca, FvXTH9 and FvXTH6. Mining of the publicly available F. vesca genome sequence yielded 28 putative XTH genes. FvXTH9 showed the highest expression level of all FvXTHs in a fruit transcriptome data set and was selected with the closely related FvXTH6 for further analysis. To investigate their role in fruit ripening in more detail, the coding sequences of FvXTH9 and FvXTH6 were cloned into the vector pYES2 and expressed in Saccharomyces cerevisiae. FvXTH9 and FvXTH6 displayed xyloglucan endotransglucosylase (XET) activity towards various acceptor substrates using xyloglucan as the donor substrate. Interestingly, FvXTH9 showed activity of mixed‐linkage glucan:xyloglucan endotransglucosylase (MXE) and cellulose:xyloglucan endotransglucosylase (CXE). The optimum pH of both FvXTH9 and FvXTH6 was 6.5. The prediction of subcellular localization suggested localization to the secretory pathway, which was confirmed by localization studies in Nicotiana tabacum. Overexpression showed that Fragaria × ananassa fruits infiltrated with FvXTH9 and FvXTH6 ripened faster and showed decreased firmness compared with the empty vector control pBI121. Thus FvXTH9 and also FvXTH6 might promote strawberry fruit ripening by the modification of cell wall components.

Systematic Analysis and Functional Validation of Citrus XTH Genes Reveal the Role of Csxth04 in Citrus Bacterial Canker Resistance and Tolerance.

In this study, we performed a comprehensive survey of xyloglucan endotransglucosylase/hydrolase (XTH) and a functional validation of Citrus sinensis (Cs) XTH genes to provide new insights into the involvement of XTHs in Xanthomonas citri subsp. citri (Xcc) infection. From the genome of sweet orange, 34 CsXTH genes with XTH characteristic domains were identified and clustered into groups I/II, IIIA, and IIIB. Except for chromosome 9, the CsXTH genes were unevenly distributed and duplicated among all chromosomes, identifying a CsXTH duplication hot spot on chromosome 4. With Xcc induction, a group of citrus canker-related CsXTHs were detected. CsXTH04 was identified as a putative candidate gene, which is up-regulated in citrus bacterial canker (CBC)-resistant varieties and induced by exogenous treatment with salicylic acid (SA) and methyl jasmonate (MeJA). CsXTH04 overexpression conferred CBC susceptibility to transgenic citrus, while CsXTH04 silencing conferred CBC resistance. Taken together, the annotation of the CsXTH family provides an initial basis for the functional and evolutionary study of this family as potential CBC-susceptible genes. CsXTH04, validated in this study, can be used in citrus breeding to improve CBC resistance.

Analysis of the Xyloglucan Endotransglucosylase/Hydrolase Gene Family during Apple Fruit Ripening and Softening.

Ethylene and xyloglucan endotransglucosylase/hydrolase (XTH) genes were important for fruit ripening and softening in 'Taishanzaoxia' apple. In this study, we found it was ACS1-1/-1 homozygotes in 'Taishanzaoxia' apple, which determined the higher transcription activity of ACS1. XTH1, XTH3, XTH4, XTH5, and XTH9 were mainly involved in the early fruit softening independent of ethylene, while XTH2, XTH6, XTH7, XTH8, XTH10, and XTH11 were predominantly involved in the late fruit softening dependent on ethylene. Overexpression of XTH2 and XTH10 in tomato resulted in the elevated expression of genes involved in ethylene biosynthesis (ACS2, ACO1), signal transduction (ERF2), and fruit softening (XTHs, PG2A, Cel2, and TBG4). In summary, the burst of ethylene in 'Taishanzaoxia' apple was predominantly determined by ACS1-1/-1 genotype, and the differential expression of XTH genes dependent on and independent of ethylene played critical roles in the fruit ripening and softening. XTH2 and XTH10 may act as a signal switch in the feedback regulation of ethylene signaling and fruit softening.

DkXTH8, a novel xyloglucan endotransglucosylase/hydrolase in persimmon, alters cell wall structure and promotes leaf senescence and fruit postharvest softening.

Fruit softening is mainly associated with cell wall structural modifications, and members of the xyloglucan endotransglucosylase/hydrolase (XTH) family are key enzymes involved in cleaving and re-joining xyloglucan in the cell wall. In this work, we isolated a new XTH gene, DkXTH8, from persimmon fruit. Transcriptional profiling revealed that DkXTH8 peaked during dramatic fruit softening, and expression of DkXTH8 was stimulated by propylene and abscisic acid but suppressed by gibberellic acid and 1-MCP. Transient expression assays in onion epidermal cells indicated direct localization of DkXTH8 to the cell wall via its signal peptide. When expressed in vitro, the recombinant DkXTH8 protein exhibited strict xyloglucan endotransglycosylase activity, whereas no xyloglucan endohydrolase activity was observed. Furthermore, overexpression of DkXTH8 resulted in increased leaf senescence coupled with higher electrolyte leakage in Arabidopsis and faster fruit ripening and softening rates in tomato. Most importantly, transgenic plants overexpressing DkXTH8 displayed more irregular and twisted cells due to cell wall restructuring, resulting in wider interstitial spaces with less compact cells. We suggest that DkXTH8 expression causes cells to be easily destroyed, increases membrane permeability and cell peroxidation, and accelerates leaf senescence and fruit softening in transgenic plants.

Identification of a group of XTHs genes responding to heavy metal mercury, salinity and drought stresses in Medicago truncatula

Xyloglucan endotransglucosylase/hydrolases (XTH) are one of the key enzymes regulating cell wall construction, extension and metabolism. In the study, 44 XTH protein genes from Medicago truncatula genome were identified using bioinformatics, microarray and RT-PCR. Each XTH was showed to possess a highly conserved domain ((D/N)-E-(I/L/F/V)-D-(F/I/L)-E-(F/L)-L-G), and most of XTHs possess four Cys in the C terminal region, which suggests the potential for generating disulfide bonds. Based on the XTH protein sequences, these XTHscan be classified into three major families and each family can be subdivided into more groups. Examination of the genomic location of XTH genes on M. truncatula chromosomes showed that the evolutional expansion of the genes was possibly attributed to localized gene duplications. To investigate the possible involvement of the XTHs responding to heavy metals and other abiotic stresses, the XTH genes were exposed to heavy metal (Hg or Cu), salt and drought stresses. There were 28, 21 and 21 MtXTH genes found to respond to HgCl2, salt and drought stresses, respectively, but their expression were different under the stresses. Some of the XTH genes were well confirmed by quantitative RT-PCR (qRT-PCR). We further specified expression of a XTH gene Medtr4g128580 (MtXTH3) under different environmental stresses, and showed that MtXTH3 was induced by Hg exposure. These results indicated that a group of MtXTHs could be differentially expressed under the environmental stresses.

Function of xyloglucan endotransglucosylase/hydrolases in rice

Although xyloglucans are ubiquitous in land plants, they are less abundant in Poales species than in eudicotyledons. Poales cell walls contain higher levels of β-1,3/1,4 mixed-linked glucans and arabinoxylans than xyloglucans. Despite the relatively low level of xyloglucans in Poales, the xyloglucan endotransglucosylase/hydrolase (XTH) gene family in rice (Oryza sativa) is comparable in size to that of the eudicotyledon Arabidopsis thaliana. This raises the question of whether xyloglucan is a substrate for rice XTH gene products, whose enzyme activity remains largely uncharacterized. This study focused on OsXTH19 (which belongs to Group IIIA of the XTH family and is specifically expressed in growing tissues of rice shoots), and two other XTHs, OsXTH11 (Group I/II) and OsXTH20 (Group IIIA), for reference, and measurements were made of the enzymatic activities of three recombinant rice XTHs, i.e. OsXTH11, OsXTH20 and OsXTH19. All three OsXTH gene products have xyloglucan endohydrolase (XEH, EC 3·2·1·151) activity, and OsXTH11 has both XEH and xyloglucan endotransglycosylase (XET, EC 2·4·1207) activities. However, these proteins had neither hydrolase nor transglucosylase activity when glucuronoarabinoxylan or mixed-linkage glucan was used as the substrate. These results are consistent with histological observations demonstrating that pOsXTH19::GUS is expressed specifically in the vicinity of tissues where xyloglucan immunoreactivity is present. Transgenic rice lines over-expressing OsXTH19 (harbouring a Cauliflower Mosaic Virus 35S promoter::OsXTH19 cDNA construct) or with suppressed OsXTH19 expression (harbouring a pOsXTH19 RNAi construct) did not show dramatic phenotypic changes, suggesting functional redundancy and collaboration among XTH family members, as was observed in A. thaliana. OsXTH20 and OsXTH19 act as hydrolases exclusively on xyloglucan, while OsXTH11 exhibits both hydrolase and XET activities exclusively on xyloglucans. Phenotypic analysis of transgenic lines with altered expression of OsXTH19 suggests that OsXTH19 and related XTH(s) play redundant roles in rice growth.