Two genes encoding GH10 xylanases are essential for the virulence of the oomycete plant pathogen Phytophthora parasitica

Abstract

Plant cell walls are pivotal battlegrounds between microbial pathogens and their hosts. To penetrate the cell wall and thereby to facilitate infection, microbial pathogens are equipped with a wide array of cell wall-degrading enzymes to depolymerize the polysaccharides in the cell wall. However, many of these enzymes and their role in the pathogenesis of microbial pathogens are not characterized, especially those from Oomycetes. In this study, we analyzed the function of four putative endo-beta-1,4-xylanase-encoding genes (ppxyn1-ppxyn4) from Phytophthora parasitica, an oomycete plant pathogen known to cause severe disease in a wide variety of plant species. All four genes belong to the glycoside hydrolase family 10 (GH10). Recombinant proteins of ppxyn1, ppxyn2, and ppxyn4 obtained from the yeast Pichia pastoris showed degrading activities toward birch wood xylan, but they behaved differently in terms of the conditions for optimal activity, thermostability, and durability. Quantitative RT-PCR revealed upregulated expression of all four genes, especially ppxyn1 and ppxyn2, during plant infection. In contrast, ppxyn3 was highly expressed in cysts and its close homolog, ppxyn4, in germinating cysts. To uncover the role of ppxyn1 and ppxyn2 in the pathogenesis of P. parasitica, we generated silencing transformants for these two genes by double-stranded RNA-mediated gene silencing. Silencing ppxyn1 and ppxyn2 reduced the virulence of P. parasitica toward tobacco (Nicotiana benthamiana) and tomato plants. These results demonstrate the crucial role of xylanase-encoding ppxyn1 and ppxyn2 in the infection process of P. parasitica.

Global Characterization of GH10 Family Xylanase Genes in Rhizoctonia cerealis and Functional Analysis of Xylanase RcXYN1 During Fungus Infection in Wheat

“…Early expression has also been observed for some xylanase genes from other fungal pathogens [25,39]. Induced expression at the early infection time suggested the importance of ppxyn1 and ppxyn2 in the pathogenicity of P. parasitica [25]. Similarly, transcriptions of both GH10 members from B. cinerea were the most abundant at the early stage, and continued increasing throughout the infection process [39].…”

“…Interestingly, RcXYN1, RcXYN2, RcXYN5, and RcXYN9 expressed at high levels even from the beginning infection to wheat and maintained the high transcriptional levels for all the tested time points (the whole infection process to wheat). Early expression has also been observed for some xylanase genes from other fungal pathogens [25,39]. Induced expression at the early infection time suggested the importance of ppxyn1 and ppxyn2 in the pathogenicity of P. parasitica [25].…”

“…Several xylanases from other fungal pathogens were also shown to have activity as necrotrophic effectors. For instance, ppxyn1 and ppxyn2 have been shown to play a crucial role in the infection process of P. parasitica [25]. In B. cinerea, BcXyl1, acting as an effector, is able to induce plant defense responses and contributes to pathogenicity [44].…”

“…Disruption of a Xyn11A of GH11 family from Botrytis cinerea had a profound effect on virulence, including delayed appearance of secondary lesions and a reduction inaverage lesion size by more than 70% [24]. In Phytophthora parasitica, ppxyn1 and ppxyn2, two xylanases from the GH10 family, play a crucial role in the pathogen infection process [25]. In Septorianodorum, xylan-degrading enzymes were highly induced when infecting Graminaceous monocotyledons, but the contribution of xylanases to pathogenicity is not clear [26,27].…”

FoEG1, a secreted glycoside hydrolase family 12 protein from Fusariumoxysporum, triggers cell death and modulates plant immunity

“…The plant cell wall is the first barrier encountered when pathogens infect plants and it is mainly composed of polysaccharide components such as pectins, hemicelluloses, celluloses, and β‐1,3‐glucans (Lai & Liou, 2018). Pathogens secrete numerous cell‐wall‐degrading enzymes (CWDEs), such as pectinases, cellulases, hemicellulases, and ligninases, to overcome the plant cell wall (Kubicek et al., 2014).…”