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Microbiology 155 (2009), 3270-3280; DOI  10.1099/mic.0.030676-0IMMEDIATE OPEN ACCESS ARTICLE
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Microbiology 155 (2009), 3270-3280; DOI  10.1099/mic.0.030676-0
© 2009 Society for General Microbiology

Small heat-shock protein HspL is induced by VirB protein(s) and promotes VirB/D4-mediated DNA transfer in Agrobacterium tumefaciens

Yun-Long Tsai1, Ming-Hsuan Wang1, Chan Gao3, Sonja Klüsener2, Christian Baron3,4, Franz Narberhaus2 and Erh-Min Lai1

1 Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan
2 Lehrstuhl für Biologie der Mikroorganismen, Ruhr-Universität Bochum, Bochum, Germany
3 Biology Department, McMaster University, Hamilton, ON, Canada
4 Département de Biochimie, Université de Montréal, Montréal, QC, Canada

Agrobacterium tumefaciens is a Gram-negative plant-pathogenic bacterium that causes crown gall disease by transferring and integrating its transferred DNA (T-DNA) into the host genome. We characterized the chromosomally encoded alpha-crystallin-type small heat-shock protein ({alpha}-Hsp) HspL, which was induced by the virulence (vir) gene inducer acetosyringone (AS). The transcription of hspL but not three other {alpha}-Hsp genes (hspC, hspAT1, hspAT2) was upregulated by AS. Further expression analysis in various vir mutants suggested that AS-induced hspL transcription is not directly activated by the VirG response regulator but rather depends on the expression of VirG-activated virB genes encoding components of the type IV secretion system (T4SS). Among the 11 virB genes encoded by the virB operon, HspL protein levels were reduced in strains with deletions of virB6, virB8 or virB11. VirB protein accumulation but not virB transcription levels were reduced in an hspL deletion mutant early after AS induction, implying that HspL may affect the stability of individual VirB proteins or of the T4S complex directly or indirectly. Tumorigenesis efficiency and the VirB/D4-mediated conjugal transfer of an IncQ plasmid RSF1010 derivative between A. tumefaciens strains were reduced in the absence of HspL. In conclusion, increased HspL abundance is triggered in response to certain VirB protein(s) and plays a role in optimal VirB protein accumulation, VirB/D4-mediated DNA transfer and tumorigenesis.

Correspondence
Erh-Min Lai
emlai{at}gate.sinica.edu.tw

Abbreviations: AS, acetosyringone; {alpha}-Hsp, {alpha}-crystallin-type small heat-shock protein; RFU, relative fluorescence units; T4SS, type IV secretion system; T-DNA, transferred DNA; Ti, tumour-inducing (plasmid)

A supplementary table of primers and a supplementary figure showing the reduced tumorigenesis efficiency of the hspL mutant are available with the online version of this paper.






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