Suppression of expression of the putative receptor-like kinase gene NRRB enhances resistance to bacterial leaf streak in rice.

Bacterial leaf streak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc) is an important disease of rice, which is responsible for the economic losses worldwide. Functional investigation of differentially expressed protein genes (DEPGs) from rice (Oryza sativa L.) upon Xoc infection provides insight into the molecular mechanism of rice-Xoc interactions. Here, we show that one of DEPGs designated NRRB plays a role in rice-Xoc interactions. NRRB, a receptor-like cytoplasmic kinase gene was preferentially expressed in leaf blades and leaf sheaths where the pathogen colonized. Its transcription was depressed by two defense-signal compounds salicylic acid and 1-aminocyclopropane-1-carboxylic-acid, but was activated by wounding and abscisic acid. Additionally, a plenty of cis-elements associated with stress responses were discovered in the promoter region of NRRB. These data suggest that NRRB is involved in stress responses. More importantly, the NRRB-suppressing rice plants exhibited enhanced resistance against BLS, with the markedly shorter average lesion length than that of the wild type. Furthermore, transcription of some salicylic acid synthesis-related and pathogenesis-related genes including PAD4, PR1a and WRKY13 in transgenic plants was activated, implying that enhanced resistance to BLS might be mediated by the activation of the SA signaling pathway. In conclusion, NRRB gene is involved in various stress responses and regulating resistance to BLS, therefore it might be one of useful genes for rice improvement in future.