OsPRMT5 methylates OsPAL1 to promote rice resistance, hindered by a <i>Xanthomonas oryzae</i> effector

Rice bacterial blight, caused by the pathogen Xanthomonas oryzae pv. oryzae (Xoo), poses a significant threat to rice crops. Arginine methylation, a post-translational modification of proteins, plays a pivotal role in transcriptional regulation, RNA processing, and the biosynthesis of plant hormones. Previous research has established that protein arginine methyltransferases (PRMTs) significantly influence protein function through arginine methylation. Nonetheless, the specific role of PRMT5 in regulating salicylic acid (SA) biosynthesis and plant immunity has been relatively unexplored. In this study, we elucidate the role of a rice protein arginine methyltransferase, OsPRMT5, in enhancing rice resistance to Xoo infection by interacting with the SA biosynthesis enzyme phenylalanine ammonia lyase 1 in rice (OsPAL1). Our results indicate that OsPRMT5 methylates OsPAL1 at the arginine residue 75, which affects the interaction between OsPRMT5 and OsPAL1 and subsequently boosts phenylalanine ammonia lyase (PAL) enzyme activity, leading to heightened SA accumulation. Conversely, compared to OsPAL1 overexpression plants in wild-type TP309 background, OsPAL1 overexpression plants in osprmt5 knockout (KO) mutants background exhibited diminished PAL activity. Furthermore, osprmt5 ospal1 double mutants demonstrated reduced resistance to bacterial blight compared to the OsPAL1-KO group. Additionally, we discovered that the Xoo effector protein PXO_01039 undermines the interaction between OsPRMT5 and OsPAL1, thereby facilitating Xoo infection. PXO_01039 binds to OsPRMT5, preventing the formation of the OsPRMT5-OsPAL1 complex, which results in decreased PAL activity and lower SA accumulation. In conclusion, our findings unveil how OsPRMT5 modulates the methylation and enzymatic activity of OsPAL1, a crucial enzyme in SA biosynthesis, to bolster plant antibacterial defenses.