An Ustilaginoidea virens glycoside hydrolase 42 protein is an essential virulence factor and elicits plant immunity as a PAMP

Abstract

Rice false smut, caused by the ascomycete fungus Ustilaginoidea virens, which infects rice florets before heading, severely threatens rice grain yield and quality worldwide. The U. virens genome encodes a number of glycoside hydrolase (GH) proteins. So far, the functions of these GHs in U. virens are largely unknown. In this study, we identified a GH42 protein secreted by U. virens, named UvGHF1, that exhibits β‐galactosidase activity. UvGHF1 not only functions as an essential virulence factor during U. virens infection, but also serves as a pathogen‐associated molecular pattern (PAMP) in Nicotiana benthamiana and rice. The PAMP activity of UvGHF1 is independent of its β‐galactosidase activity. Moreover, UvGHF1 triggers cell death in N. benthamiana in a BAK1‐dependent manner. Ectopic expression of UvGHF1 in rice induces pattern‐triggered immunity and enhances rice resistance to fungal and bacterial diseases. RNA‐seq analysis revealed that UvGHF1 expression in rice not only activates expression of many defence‐related genes encoding leucine‐rich repeat receptor‐like kinases and WRKY and ERF transcription factors, but also induces diterpenoid biosynthesis and phenylpropanoid biosynthesis pathways. Therefore, UvGHF1 contributes to U. virens virulence, but is also recognized by the rice surveillance system to trigger plant immunity.

UvHOS3‐mediated histone deacetylation is essential for virulence and negatively regulates ustilaginoidin biosynthesis in Ustilaginoidea virens

“…The UvHos3 deletion mutants were generated through homologous recombination induced by the CRISPR/Cas9 system (Li et al., 2019 ; Zou et al., 2023 ). Briefly, both flanking sequences (c. 1 kb) of the target gene were PCR‐amplified with the primers listed in Table S1 .…”

Tilletia horrida glycoside hydrolase family 128 protein, designated ThGhd_7, modulates plant immunity by blocking reactive oxygen species production

“…Recently, the GH42 protein UvGHF1 from Ustilaginoidea virens was found to be an essential virulence factor and is recognised ad a PAMP in N. benthamiana and rice (Zou et al, 2023).…”