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Overexpression of the HspL Promotes Agrobacterium tumefaciens Virulence in Arabidopsis Under Heat Shock Conditions

February 2015 , Volume 105 , Number  2
Pages  160 - 168

Hau-Hsuan Hwang, Yin-Tzu Liu, Si-Chi Huang, Chin-Yi Tung, Fan-Chen Huang, Yun-Long Tsai, Tun-Fang Cheng, and Erh-Min Lai

First author: Department of Life Sciences and Ph.D. Program in Microbial Genomics, National Chung Hsing University, Taichung, 402, Taiwan; second, third, fourth, fifth, and seventh authors: Department of Life Sciences, National Chung Hsing University; fifth author: Ph.D. Program in Microbial Genomics, National Chung Hsing University and Academia Sinica, Taichung, Taiwan, 402; and sixth and eighth authors: Institute of Plant and Microbial Biology, Academia Sinica, Taipei, 115, Taiwan.

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Accepted for publication 15 August 2014.

Agrobacterium tumefaciens transfers a specific DNA fragment from the resident tumor-inducing (Ti) plasmid and effector virulence (Vir) proteins to plant cells during infection. A. tumefaciens VirB1-11 and VirD4 proteins assemble as the type IV secretion system (T4SS), which mediates transfer of the T-DNA and effector Vir protein into plant cells, thus resulting in crown gall disease in plants. Previous studies revealed that an α-crystallin-type, small heat-shock protein (HspL) is a more effective VirB8 chaperone than three other small heat-shock proteins (HspC, HspAT1, and HspAT2). Additionally, HspL contributes to efficient T4SS-mediated DNA transfer and tumorigenesis under room-temperature growth. In this study, we aimed to characterize the impact of HspL on Agrobacterium-mediated transformation efficiency under heat-shock treatment. During heat shock, transient transformation efficiency and VirB8 protein accumulation were lower in the hspL deletion mutant than in the wild type. Overexpression of HspL in A. tumefaciens enhanced the transient transformation efficiency in root explants of both susceptible and recalcitrant Arabidopsis ecotypes. In addition, the reduced transient transformation efficiency during heat stress was recovered by overexpression of HspL in A. tumefaciens. HspL may help maintain VirB8 homeostasis and elevate Agrobacterium-mediated transformation efficiency under both heat-shock and nonheat-shock growth.

© 2015 The American Phytopathological Society