The rice serine/threonine protein kinase OsPBL1 (ORYZA SATIVA ARABIDOPSIS PBS1-LIKE 1) is potentially involved in resistance to rice stripe disease

Rice stripe disease is caused by the rice stripe virus (RSV) which is transmitted by the small brown plant hopper (SBPH). This disease significantly restricts rice productivity in East Asia. Major RSV resistance quantitative trait loci (QTLs) have been shown to be located on chromosome 11 in several resistant cultivars. However, the molecular identities of these QTLs are largely unknown. In this study, we identified the serine/threonine protein kinase OsPBL1 (ORYZA SATIVA ARABIDOPSIS PB S1-LIKE 1), a potential resistance gene to rice stripe disease, by reverse genetic screening with T-DNA insertional mutant lines. The OsPBL1 protein is highly conserved among various monocots and dicots, including Arabidopsis. Specifically, OsPBL1 exhibits 67 % amino acid sequence identity to AtPBS1 (AVRPPHB SUSCEPTIBLE1), a positive regulator of effector-triggered immunity (ETI) in Arabidopsis. Moreover, we show here that OsPBL1 transcripts are abundantly expressed in the leaves of Dongjin seedlings-an RSV-resistant-under normal growth conditions. Exogenous treatment with defense-related phytohormones such as cytokinin and salicylic acid increased the expression of OsPBL1. This gene is also modulated by the circadian rhythm. Furthermore, OsPBL1, OsPR1b, and OsPR2 transcripts were up-regulated to higher levels by SBPH treatment, which was specifically observed in RSV-resistant varieties. The OsPBL1 protein was found to localize to the nucleus and to be cleaved upon attack with either healthy or infected SBPHs. Taken together, our data indicate that OsPBL1 undergoes various transcriptional and post-translational modifications upon SBPH and/or RSV attack, similar to Arabidopsis PBS1. We propose that OsPBL1 is involved in antiviral defense signaling pathways in rice.