Genome-Wide Identification of the Xyloglucan endotransglucosylase/Hydrolase (XTH) and Polygalacturonase (PG) Genes and Characterization of their Role in Fruit Softening of Sweet Cherry

Fruit firmness is an important economical trait in sweet cherry (Prunus avium L.) where the change of this trait is related to cell wall degradation. Xyloglucan endotransglycosylase/hydrolase (XTH) and polygalacturonases (PGs) are critical cell-wall-modifying enzymes that occupy a crucial position in fruit ripening and softening. Herein, we identified 18 XTHs and 45 PGs designated PavXTH1-18 and PavPG1-45 based on their locations in the genome of sweet cherry. We provided a systematical overview of PavXTHs and PavPGs, including phylogenetic relationships, conserved motifs, and expression profiling of these genes. The results showed that PavXTH14, PavXTH15 and PavPG38 were most likely to participated in fruit softening owing to the substantial increment in expression during fruit development and ripening. Furthermore, the phytohormone ABA, MeJA, and ethephon significantly elevated the expression of PavPG38 and PavXTH15, and thus promoted fruit softening. Importantly, transient expression PavXTH14, PavXTH15 and PavPG38 in cherry fruits significantly reduced the fruit firmness, and the content of various cell wall components including hemicellulose and pectin significantly changed correspondingly in the transgenic fruit. Taken together, these results present an extensive analysis of XTHs and PGs in sweet cherry and provide potential targets for breeding softening-resistant sweet cherry cultivars via manipulating cell wall-associated genes.

COMPARATIVE PROTEOMIC ANALYSIS OF THE THICK-WALLED RAY FORMATION PROCESS OF HALOXYLON AMMODENDRON IN THE GURBANTUNGGUT DESERT, CHINA

Thick-walled ray cells of Haloxylon ammodendronwere first reported by Zhou and Gong in 2017, but their formation mechanism remains unknown. In this study, we performeda proteomic analysis of ray cell wall formation in the xylem. H. ammodendronin Shihezi exhibits a thicker ray cell wall than that in Jinghe. During the process of cell wall biosynthesisin the xylem of H. ammodendron, the nonspecific lipid-transfer protein and beta expansin EXPB2.1 (Mirabilis jalapa) first loosen the cell wall, and this step is followed by extension and expansion. Subsequently, xyloglucan endotransglycosylase/hydrolase 1 cleaves and linksthe xyloglucan chains. Photosystem I P700 apoprotein A1, reversibly glycosylated polypeptide 1 and GDP-mannose-3′,5′-epimerase are involved in the cellulose, hemicellulose and pectin biosynthesis processes in the cell wall by providing components or energy. Finally, the proteins involved in phenylpropanoid biosynthesis promote lignification of the ray cell wall and complete the biosynthetic process of the cell wall.

Identification and response analysis of xyloglucan endotransglycosylase/hydrolases (XTH) family to fluoride and aluminum treatment in Camellia sinensis

Background Xyloglucan endotransglycosylase/hydrolases (XTH) can disrupt and reconnect the xyloglucan chains, modify the cellulose-xyloglucan complex structure in the cell wall to reconstruct the cell wall. Previous studies have reported that XTH plays a key role in the aluminum (Al) tolerance of tea plants (Camellia sinensis), which is a typical plant that accumulates Al and fluoride (F), but its role in F resistance has not been reported. Results Here, 14 CsXTH genes were identified from C. sinensis and named as CsXTH1–14. The phylogenetic analysis revealed that CsXTH members were divided into 3 subclasses, and conserved motif analysis showed that all these members included catalytic active region. Furthermore, the expressions of all CsXTH genes showed tissue-specific and were regulated by Al3+ and F− treatments. CsXTH1, CsXTH4, CsXTH6–8 and CsXTH11–14 were up-regulated under Al3+ treatments; CsXTH1–10 and CsXTH12–14 responded to different concentrations of F− treatments. The content of xyloglucan oligosaccharide determined by immunofluorescence labeling increased to the highest level at low concentrations of Al3+ or F− treatments (0.4 mM Al3+ or 8 mg/L F−), accompanying by the activity of XET (Xyloglucan endotransglucosylase) peaked. Conclusion In conclusion, CsXTH activities were regulated by Al or F via controlling the expressions of CsXTH genes and the content of xyloglucan oligosaccharide in C. sinensis roots was affected by Al or F, which might finally influence the elongation of roots and the growth of plants.

The Sequence and Integrated Analysis of Competing Endogenous RNAs Originating from Tea Leaves Infected by the Pathogen of Tea Leaf Spot, Didymella segeticola

Tea leaf spot, caused by Didymella segeticola (Q. Chen) Q. Chen, Crous & L. Cai, is an important disease, which negatively affects the productivity and the quality of tea leaves. During infection by the pathogen, competing endogenous RNAs (ceRNAs) from tea leaves could contribute to achieving pathogenicity. In this study, circular RNAs (circRNAs) and long non-coding RNAs (lncRNAs), constituting ceRNAs, which share binding sites on microRNAs (miRNAs), and messenger RNAs (mRNAs), from infected and uninfected leaves of tea (Camellia sinensis cv. Fuding-dabaicha) were sequenced and analyzed, and the identity and expression levels of the target genes of miRNA-mRNA and miRNA-lncRNA/circRNA were predicted. Analysis indicated that ten mRNAs were bound by 18 miRNAs, 66 lncRNAs were bound by 40 miRNAs, and 29 circRNAs were bound by 17 miRNAs, respectively. For the regulation modes of ceRNAs, five ceRNA pairs were identified by the correlation analysis of lncRNA–miRNA–mRNA. For instance, expression of the xyloglucan endotransglycosylase (XET) gene in infected leaves was down-regulated at the level of mRNA through miRNA PC-5p-3511474_3 binding with lncRNA TEA024202.1:MSTRG.37074.1. Gene annotation indicated that expression of this gene was significantly enriched in cell wall biogenesis and in the pathway of plant hormone signal transduction. The functional analysis of ceRNAs isolated from infected tea leaves will provide a valuable resource for future research on D. segeticola pathogenicity.

Exogenously Applied Chitosan and Chitosan Nanoparticles Improved Apple Fruit Resistance to Blue Mold, Upregulated Defense-Related Genes Expression and Maintained Fruit Quality

Blue rot disease caused by Penicillium expansum is one of the most widespread fungal diseases that affects apples worldwide. This work was to verify the effect of chitosan (2 and 4 g/L) and its nano-form (0.2 and 0.4 g/L) against blue rot disease on apples and their effect on the expression of six defense-related genes as well as fruit quality parameters. Regarding disease incidence, in most cases, chitosan NPs performed better as compared to their raw materials for both artificial and natural infections. The highest efficacy was obtained for chitosan NPs at 0.4 g/L for artificial and natural infection in both 2019 and 2020 seasons. All treatments kept fruit quality parameters regarding firmness, total soluble solids, and titratable acidity for artificial and natural infection in both seasons. As expected, the exogenous application of chitosan NPs and bulk form triggered an increase in the expression levels of six defense-related genes including chitinase, peroxidase, β-1,3-glucanase, Xyloglucan endotransglycosylase (XET), pathogenesis-related protein (PR8), and phenylalanine ammonia lyase-1 (PAL1). Moreover, the highest mRNA quantity of all the studied genes was detected in leaves treated with chitosan NPs at both concentrations compared to other treatments. Chitosan NPs can be considered an eco-friendly and effective approach against blue mold of apples and can be integrated into management programs to maintain postharvest quality and extend the shelf life of fruits.

Xyloglucan endotransglycosylase/hydrolase increases tightly-bound xyloglucan and chain number but decreases chain length contributing to the defense response that Glycine max has to Heterodera glycines

The Glycine max xyloglucan endotransglycosylase/hydrolase (EC 2.4.1.207), GmXTH43, has been identified through RNA sequencing of RNA isolated through laser microdissection of Heterodera glycines-parasitized root cells (syncytia) undergoing the process of defense. Experiments reveal that genetically increasing XTH43 transcript abundance in the H. glycines-susceptible genotype G. max[Williams 82/PI 518671] decreases parasitism. Experiments presented here show decreasing XTH43 transcript abundance through RNA interference (RNAi) in the H. glycines-resistant G. max[Peking/PI 548402] increases susceptibility, but it is unclear what role XTH43 performs. The experiments presented here show XTH43 overexpression decreases the relative length of xyloglucan (XyG) chains, however, there is an increase in the amount of those shorter chains. In contrast, XTH43 RNAi increases XyG chain length. The experiments show that XTH43 has the capability to function, when increased in its expression, to limit XyG chain extension. This outcome would likely impair the ability of the cell wall to expand. Consequently, XTH43 could provide an enzymatically-driven capability to the cell that would allow it to limit the ability of parasitic nematodes like H. glycines to develop a feeding structure that, otherwise, would facilitate parasitism. The experiments presented here provide experimentally-based proof that XTHs can function in ways that could be viewed as being able to limit the expansion of the cell wall.

Genome-wide characterization and expression profiling analysis of the xyloglucan endotransglycosylase/hydrolase gene family in Brachypodium distachyon

Background: Xyloglucan endotransglucosylase/hydrolases (XTHs) are a class of cell wall-associated enzymes involved in the construction and remodeling of cellulose/xyloglucan crosslinks. However, knowledge of this gene family in the model monocot Brachypodium distachyon is limited. Results: A total of 29 BdXTH genes were identified from the reference genome, and these were further divided into three main groups (Group I/II, Group III, and the Ancestral Group) through comparative phylogenetic analysis. Gene structure and protein motif analysis indicate that closely clustered BdXTH genes are relatively conserved within each group. A highly conserved amino acid domain (DEIDFEFLG) responsible for catalytic activity was identified in all BdXTH proteins. We detected three pairs of segmentally duplicated BdXTH genes and five groups of tandemly duplicated BdXTH genes, which have played important roles in the expansion of the BdXTH gene family. Cis -elements related to hormones, growth, and abiotic stress responses were identified in the promoters of each BdXTH gene. Most BdXTH genes have distinct expression patterns in different tissues and growth stages. Furthermore, when roots were treated with two abiotic stresses (salinity and drought) and four plant hormones (IAA, auxin; GA3, gibberellin; ABA, abscisic acid and BR, brassinolide), the expression levels of many BdXTH genes changed significantly, suggesting possible roles in response to various environmental stimuli and plant hormones. Conclusion: In this study, we performed genome-wide identification, characterization, and expression pattern analysis of the XTH gene family in Brachypodium, which provide valuable information for further elucidation of the biological functions of BdXTH genes in the model grass B. distachyon.