The Arabidopsis Malectin-Like/LRR-RLK IOS1 Is Critical for BAK1-Dependent and BAK1-Independent Pattern-Triggered Immunity

• Published in: The Plant cell 2016-07, Vol.28 (7), p.1701-1721
• Main Authors: Yeh, Yu-Hung, Panzeri, Dario, Kadota, Yasuhiro, Huang, Yi-Chun, Huang, Pin-Yao, Tao, Chia-Nan, Roux, Milena, Chien, Hsiao-Chiao, Chin, Tzu-Chuan, Chu, Po-Wei, Zipfel, Cyril, Zimmerli, Laurent
• Format: Article
• Language: English
• Subjects: Aminobutyrates - metabolism; Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - microbiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; Oomycetes; Plant Immunity - genetics; Plant Immunity - physiology; Protein Kinases - genetics; Protein Kinases - metabolism; Protein Serine-Threonine Kinases - genetics; Protein Serine-Threonine Kinases - metabolism; Pseudomonas syringae; Pseudomonas syringae - pathogenicity
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.16.00313

Plasma membrane-localized pattern recognition receptors (PRRs) such as FLAGELLIN SENSING2 (FLS2), EF-TU RECEPTOR (EFR), and CHITIN ELICITOR RECEPTOR KINASE1 (CERK1) recognize microbe-associated molecular patterns (MAMPs) to activate pattern-triggered immunity (PTI). A reverse genetics approach on genes responsive to the priming agent β-aminobutyric acid (BABA) revealed IMPAIRED OOMYCETE SUSCEPTIBILITY1 (IOS1) as a critical PTI player. Arabidopsis thaliana ios1 mutants were hypersusceptible to Pseudomonas syringae bacteria. Accordingly, ios1 mutants showed defective PTI responses, notably delayed upregulation of the PTI marker gene FLG22-INDUCED RECEPTOR-LIKE KINASE1, reduced callose deposition, and mitogen-activated protein kinase activation upon MAMP treatment. Moreover, Arabidopsis lines overexpressing IOS1 were more resistant to bacteria and showed a primed PTI response. In vitro pull-down, bimolecular fluorescence complementation, coimmunoprecipitation, and mass spectrometry analyses supported the existence of complexes between the membrane-localized IOS1 and BRASSINOSTEROID INSENSITIVE1-ASSOCIATED KINASE1 (BAK1)-dependent PRRs FLS2 and EFR, as well as with the BAK1-independent PRR CERK1. IOS1 also associated with BAK1 in a ligand-independent manner and positively regulated FLS2-BAK1 complex formation upon MAMP treatment. In addition, IOS1 was critical for chitinmediated PTI. Finally, ios1 mutants were defective in BABA-induced resistance and priming. This work reveals IOS1 as a novel regulatory protein of FLS2-, EFR-, and CERK1-mediated signaling pathways that primes PTI activation.