The rice Raf‐like MAPKKK OsILA1 confers broad‐spectrum resistance to bacterial blight by suppressing the OsMAPKK4–OsMAPK6 cascade

• Published in: Journal of integrative plant biology 2021-10, Vol.63 (10), p.1815-1842
• Main Authors: Chen, Jie, Wang, Lihan, Yang, Zeyu, Liu, Hongbo, Chu, Chuanliang, Zhang, Zhenzhen, Zhang, Qinglu, Li, Xianghua, Xiao, Jinghua, Wang, Shiping, Yuan, Meng
• Format: Article
• Language: English
• Subjects: Blight; Disease Resistance; Domains; Genetic analysis; Genomes; Host-Pathogen Interactions; Kinases; Leaf angle; MAP kinase; MAP Kinase Kinase 4 - metabolism; MAP Kinase Kinase Kinases - metabolism; MAP Kinase Signaling System; MAPK cascade; Mitogen-Activated Protein Kinase 6 - metabolism; Oryza - enzymology; Oryza sativa; OsILA1; Phosphorylation; Protein kinase; Raf protein; Raf‐like MAPKKK; Rice; Threonine; Xanthomonas; Xanthomonas oryzae
• ISSN: 1672-9072; 1744-7909
• DOI: 10.1111/jipb.13150

Mitogen‐activated protein kinase kinase kinase (MAPKKK) are the first components of MAPK cascades, which play pivotal roles in signaling during plant development and physiological processes. The genome of rice encodes 75 MAPKKKs, of which 43 are Raf‐like MAPKKKs. The functions and action modes of most of the Raf‐like MAPKKKs, whether they function as bona fide MAPKKKs and which are their downstream MAPKKs, are largely unknown. Here, we identified the osmapkkk43 mutant, which conferred broad‐spectrum resistance to Xanthomonas oryzae pv. oryzae (Xoo), the destructive bacterial pathogen of rice. Oryza sativa (Os)MAPKKK43 encoding a Raf‐like MAPKKK was previously known as Increased Leaf Angle 1 (OsILA1). Genetic analysis indicated that OsILA1 functioned as a negative regulator and acted upstream of the OsMAPKK4–OsMAPK6 cascade in rice–Xoo interactions. Unlike classical MAPKKKs, OsILA1 mainly phosphorylated the threonine 34 site at the N‐terminal domain of OsMAPKK4, which possibly influenced the stability of OsMAPKK4. The N‐terminal domain of OsILA1 is required for its homodimer formation and its full phosphorylation capacity. Taken together, our findings reveal that OsILA1 acts as a negative regulator of the OsMAPKK4–OsMAPK6 cascade and is involved in rice–Xoo interactions. The rice Raf‐like MAPKKK INCREASED LEAF ANGLE 1 (OsILA1) negatively modulates broad‐spectrum resistance to bacterial blight. OsILA1 mainly directly phosphorylates the T34 residue in the N terminus of OsMAPKK4 and reduces its protein stability, thereby negatively regulating the OsMAPKK4‐OsMAPK6 cascade.