Xanthomonas oryzae pv. oryzae is the causal agent of the bacterial blight in rice, which invades the host rice plant through injecting a myriad of effector proteins through a structure called type Ⅲ secretion system, thereafter, these effectors are also called type Ⅲ effectors. There are two groups of type Ⅲ effectors: TAL (Transcription Activator-Like) effectors that specifically bind to the promoter region of particular host genes and regulate host gene transcription and Non-TAL effectors that bind to host gene products and manipulate the host immune system.

In this thesis, I present the work of three projects. First, I, and my colleagues demonstrated two TAL effectors, PthXo3 and AvrXa7 mediate susceptibility in rice by specifically binding to the promoter EBE (Effector-Binding Element) and activating transcription of the host gene Os-11N3 (Chapter 2). Second, I elucidated that another major virulence effector PthXo2 specifically targets EBE in the promoter of another host gene OsSWEET13 and induces susceptibility to bacterial blight only in indica rice but not in japonica rice, functional analysis confirmed that OsSWEET13 is a sucrose transporter that mediates the sucrose efflux from cytoplasm to apoplasm (Chapter 3). Finally, I investigated the XopZ-mediated virulence function in rice and found that it stabilizes a putative host E3 ubiquitin ligase PBP in the nucleus (Chapter 4). The revelation of modes of action of these bacterial effectors in rice leads to a better mechanistic understanding of host-pathogen interactions and the plant immune system, as well as effective strategies to defeat plant pathogens.