OsRACK1A Scaffolds MAPK Signaling to Mediate Rice Immunity Against Xanthomonas oryzae pv. oryzicola

Bacterial leaf streak (BLS), caused by Xanthomonas oryzae pv. oryzicola (Xoc), poses a severe threat to rice production. Despite its agricultural impact, the molecular mechanisms underlying rice resistance to Xoc remain largely elusive. In this study, we report that OsRACK1A, a conserved scaffold protein, positively regulates rice resistance to Xoc by modulating the MAPK signaling. Transgenic rice plants overexpressing OsRACK1A exhibit enhanced resistance to Xoc, whereas knockdown lines display heightened susceptibility. This compromised resistance was associated with attenuated activation of mitogen-activated protein kinase (MAPK) cascades and suppressed expression of defense-related genes. Further analysis reveals that OsRACK1A physically interacts with OsMPK3 and OsMPK6 in both the nucleus and the cytoplasm. Additionally, we find that OsRACK1A associates with its homolog, OsRACK1B, suggesting these proteins may form a heteromeric complex to coordinate MAPK activation. Collectively, our findings identify OsRACK1A as a critical positive regulator of rice immunity against Xoc and highlight its potential as a genetic target for breeding disease-resistant crops.