Genetic and Biochemical Characterization of AIN3 in Plant Immunity

Gram-negative phytobacteria deliver a collection of type III effectors inside of host cells during pathogenesis, where some type III effectors were confirmed to have roles of suppressing host immunity in compatible plants. However, the exact biological and biochemical functions of most effector is still exclusive. We identified a bacterial type III effector, AvrRxo1, from Xanthomonas oryzae pv. oryzicola that could be translocated into plant nucleus. In aim to identify Arabidopsis genes regulated by AvrRxo1, we performed RNA-seq based gene expression profiling by using transgenic Arabidopsis plants expressing either wild type or mutant AvrRxo1. A NAC transcription factor, designated as AIN3, was identified as one of the AvrRxo1 induced genes.  Interestingly, Ain3 could specifically interact with AvrRxo1 in yeast two-hybrid assays and co-immunoprecipitation in vivo. We generated transgenic Arabidopsis with overexpression of AIN3 (AIN3-ox) and also identified T-DNA knockout line of ain3. Spray-inoculated Pseudomonas syringae pv. tomato DC3000 (delta CEL) caused more severe disease lesions on AIN3-ox plants than that of the wild type plants. However, the bacterial proliferation was not significant difference between AIN3-ox and wild type Arabidopsis plants. Therefore, AIN3 may have a role of AvrRxo1-induced lesion development, and AvrRxo1 can control AIN3 both on transcription and protein levels. More detailed biochemical analysis of AIN3/AvrRxo1 interactions will be presented in the poster.