Roles of Effectors RSp0213 and PopP3 in Virulence of Ralstonia solanacearum
Date Issued
2014
Date
2014
Author(s)
Chu, Tai-Hsiang
Abstract
Ralstonia solanacearum, the causal bacterium of bacteria wilt (BW), causes severe production losses on many important crops worldwide. R. solanacearum phylotype I strains confer varied degrees of virulence/aggressiveness on tomato plants; however, genetic information on pathogen virulence-related factors is still very limited. To uncover virulence-related factors, genomes of four R. solanacearum phylotype I strains with different virulence were sequenced. A putative effector protein RSp0213 is present in medium-virulence and low-virulence strain such as Pss4 and Pss216, but absent in high-virulnece strain such as Pss190. This study aimed to elucidate roles of RSp0213 in R. solanacearum virulence and plant-bacterium interaction. Diruption of RSp0213 in medium-virulence strain Pss4 resulted in increased bacterial virulence in tomato, while RSp0213 overexpression in high-virulence strain Pss190 leads to decreased bacterial virulence, evidencing a decisive role of RSp0213 in R. solanacearum virulence. Additionally, transient local overexpression of RSp0213 in Nicotiana benthamiana leaves led to cell death. Virus-mediated overexpression of RSp0213 in tomato also caused cell death, reduced plant growth, increased expression of marker genes involved in defense hormones and hypersensitive-response signaling pathways, and enhanced resistance to the high-virulence strain Pss190. Furthermore, GFP-tagged RSp0213 colocalizes with cell membrane of N. benthamiana and membrane localization is required for its functions. These results suggest that RSp0213 can be recognized by host cell, leading to induced defense response and thus reduced virulence of RSp0213-containing R. solanacearum strains. The absence of this effector enables high-virulence strains escape from host recognition, leading to the high virulence. The second part of this thesis aimed to uncover a YopJ-type effector protein Pseudomonas outer protein P 3 (PopP3) unique to a high-virulence strain Pss190. Our previous study showed that overexpression of popP3 in Rs medium-virulence strain Pss4 led to increased bacterial virulence in tomato. Transient overexpression of popP3 in tomato suppresses pathogen-associated molecular patterns (PAMPs)-triggered immunity (PTI) related callose deposition. popP3 transcripts was positively regulated by the type III secretion system (T3SS) regulator HrpG. Furthemore, This study proved the mitochondria localization of PopP3 in plant cell is critical to it function on tomato. These results together suggest that PopP3 is a T3SS effector and contributes to the virulence of R. solanacearum by suppressing plant defense response which related to mitochondrial functions.
Subjects
青枯病菌
效應蛋白
RSp0213
PopP3
致病力
effector-triggered immunity
effector-triggered susceptibility
Type
thesis
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