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Auxin-responsive SlXTH3 promotes Ralstonia solanacearum infection by modulating lateral root development and root
Xiaoyu Zheng1,2, Xuanwei Du1,2, Junming Chen1,2
1School of Breeding and Multiplication (Sanya Institute of Breeding and Multiplication), Hainan University, Sanya, 572025, China.
Key Message:
SlXTH3 promotes tomato lateral root development and cell wall remodeling, which facilitate early root colonization by Ralstonia solanacearum and increase susceptibility to bacterial wilt. Ralstonia solanacearum is a highly destructive soil-borne bacterial pathogen whose infection typically initiates in the root system and is accompanied by remodeling of host root development and defense responses. The results of this study showed that, during the early infection of tomato roots, R. solanacearum preferentially colonized lateral root emergence sites and promoted lateral root development, thereby generating additional potential sites favorable for bacterial colonization. Further analyses revealed that, during the early stage of R. solanacearum infection, endogenous auxin accumulation was significantly induced in tomato root tissues, accompanied by the transcriptional upregulation of a group of cell wall remodeling-related genes with potential auxin responsiveness. Expression analysis showed that SlXTH3, a xyloglucan endotransglycosylase/hydrolase gene predominantly expressed in roots, was significantly upregulated during the early stage of R. solanacearum infection. Overexpression of SlXTH3 promoted lateral root formation in tomato seedlings and enhanced early colonization of tomato roots by R. solanacearum, whereas RNAi-mediated silencing of SlXTH3 showed the opposite tendency. In addition, XTH3-overexpressing lines showed increased xyloglucan endotransglycosylase (XET) activity and hemicellulose content in root tissues and suppressed flg22-induced reactive oxygen species (ROS) bursts, whereas SlXTH3-silenced lines displayed stronger ROS bursts and root immune outputs. Further experiments showed that overexpression of SlXTH3 promoted disease progression and bacterial proliferation within plants, whereas silencing SlXTH3 helped attenuate disease development. Collectively, SlXTH3 is a key susceptibility factor of R. solanacearum during tomato root infection; pathogen exploitation of SlXTH3-mediated lateral root development and immune-response suppression promotes infection establishment and aggravates disease.