RBB1 negatively regulates rice disease resistance by modulating protein glycosylation

ABSTRACT Glycosylation, a prevalent post‐translational modification in eukaryotic secreted and membrane‐associated proteins, plays a pivotal role in diverse physiological and pathological processes. Although UDP‐ N‐ acetylglucosamine (UDP‐GlcNAc) is essential for this modification, the specific glycosylation mechanisms during plant leaf senescence and defense responses remain poorly understood. In our research, we identified a novel rice mutant named rbb1 (resistance to blast and bacterial blight1), exhibiting broad‐spectrum disease resistance. This mutant phenotype results from a loss‐of‐function mutation in the gene encoding glucosamine‐6‐phosphate acetyltransferase, an important enzyme in D‐glucosamine 6‐phosphate acetylation. The rbb1 mutant demonstrates enhanced defense responses, evident in increased resistance to rice blast and bacterial blight, along with the upregulation of defense‐response genes. Various biochemical markers indicate an activated defense mechanism in the rbb1 mutant, such as elevated levels of reactive oxygen species and malondialdehyde, reduced enzyme activity and UDP‐GlcNAc content, and decreased expression of N‐ glycan and O‐ glycan modifying proteins. Moreover, proteome analysis of N‐ glycosylation modifications reveals alterations in the N‐ glycosylation of several disease‐resistance‐related proteins, with a significant reduction in Prx4 and Prx13 in rbb1 ‐1. Additionally, the knockout of Prx4 or Prx13 also enhances resistance to Xanthomonas oryzae pv. oryzae ( Xoo ) and Magnaporthe oryzae ( M. oryzae ). This study uncovers a novel mechanism of defense response in rice, suggesting potential targets for the development of disease‐resistant varieties.