Altered Expression of Genes Implicated in Xylan Biosynthesis Affects Penetration Resistance against Powdery Mildew

Abstract

Heteroxylan has recently been identified as an important component of papillae, which are formed during powdery mildew infection of barley leaves. Deposition of heteroxylan near the sites of attempted fungal penetration in the epidermal cell wall is believed to enhance the physical resistance to the fungal penetration peg and hence to improve pre-invasion resistance. Several glycosyltransferase (GT) families are implicated in the assembly of heteroxylan in the plant cell wall, and are likely to work together in a multi-enzyme complex. Members of key GT families reported to be involved in heteroxylan biosynthesis are up-regulated in the epidermal layer of barley leaves during powdery mildew infection. Modulation of their expression leads to altered susceptibility levels, suggesting that these genes are important for penetration resistance. The highest level of resistance was achieved when a GT43 gene was co-expressed with a GT47 candidate gene, both of which have been predicted to be involved in xylan backbone biosynthesis. Altering the expression level of several candidate heteroxylan synthesis genes can significantly alter disease susceptibility. This is predicted to occur through changes in the amount and structure of heteroxylan in barley papillae.

Plant cell wall‐mediated immunity: cell wall changes trigger disease resistance responses

“…For example, plants with enhanced levels of wall-bound xylose, as occurs in the Arabidopsis de-etiolated3 (det3) and irx6 mutants (Brown et al, 2005;Rogers et al, 2005), or with modifications in the xyloglucan structure, as in the case of the Arabidopsis xyl1-2 mutant (Sampedro et al, 2010), show an enhanced resistance to the necrotrophic fungus P. cucumerina (Table 1, Figure 1d; Delgado-Cerezo et al, 2012). Similarly, barley transgenic plants co-expressing glycosyltransferase-encoding genes responsible for xylan biosynthesis affected penetration resistance against Blumeria graminis (Table S1; Chowdhury et al, 2017). In contrast, Arabidopsis er plants, impaired in ERECTA receptor-like kinase that harbours a leucine-rich repeat (LRR) ectodomain (ED), and agb1 and agg1 agg2 mutants, impaired in the Gß and Gc subunits of heterotrimeric G proteins, havebesides other cell wall alterationsa reduced xylose content, and are hyper-susceptible to the necrotrophic fungus P. cucumerina (Table 1; Llorente et al, 2005;S anchez-Rodr ıguez et al, 2009;Delgado-Cerezo et al, 2012).…”

Non-Starch Polysaccharides in Durum Wheat: A Review

“…These papillae contain the (1,3)-β-glucan, callose, as their main polysaccharide component but, in addition, contain arabinoxylans, cellulose and phenolics; most of the latter is probably ferulic acid [111]. Furthermore, genes involved in arabinoxylan biosynthesis influence resistance to fungal penetration in barley [112]. This situation is likely to also occur in durum, where it has been highlighted how xylan arabinosylation explain a protective function against the cell wall from fungal enzymatic degradation [113].…”

A Genomic Perspective on the Evolutionary Diversity of the Plant Cell Wall

“…GT43 family genes encode putative xylosyltransferases required for synthesizing the xylan backbone [ 85 , 86 ]. Some members of the GT61 family encode putative arabinosyltransferases that mediate the α-1,3-Ara f substitutions of xylan [ 87 , 88 ]. Given that the attachment of ferulate to the arabinosyl residue leads to the formation of cross-links between the arabinoxylans via oxidative coupling of ferulic acid residues, the arabinosyl side chains of arabinoxylans is considered essential for the formation of the xylan network.…”

“…It is speculated that an increase in gene copy number could contribute to enhancing the potential for differential expression regulation in different types of cells in the commelinid monocotyledons, and may also facilitate the acquisition of novel functions associated with the synthesis of glucuronoarabinoxylan. The GT61 family also contains a gene encoding a putative xylosyltransferase involved in mediating the xylosyl substitution of arabinosyl residues in the xylan backbone [ 88 , 92 ], and functional analysis of O. sativa GT43 has revealed the functional diversity of certain GT43 members in xylan biosynthesis [ 93 ]. Additionally, the members of GT43 show a diversity not only with respect to predicted protein structures, but also in gene expression patterns.…”