Small heat-shock protein HspL is induced by VirB protein(s) and promotes VirB/D4-mediated DNA transfer in Agrobacterium tumefaciens.
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.
Tsai
Yun-Long
YL
Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan.
Wang
Ming-Hsuan
MH
Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan.
Gao
Chan
C
Biology Department, McMaster University, Hamilton, ON, Canada.
Klüsener
Sonja
S
Lehrstuhl für Biologie der Mikroorganismen, Ruhr-Universität Bochum, Bochum, Germany.
Baron
Christian
C
Département de Biochimie, Université de Montréal, Montréal, QC, Canada.|Biology Department, McMaster University, Hamilton, ON, Canada.
Narberhaus
Franz
F
Lehrstuhl für Biologie der Mikroorganismen, Ruhr-Universität Bochum, Bochum, Germany.
Lai
Erh-Min
EM
Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan.
D000098:Acetophenones / Q000378:metabolism; D016960:Agrobacterium tumefaciens / Q000502:physiology*; D001426:Bacterial Proteins / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D022761:Gene Transfer, Horizontal; D050888:Heat-Shock Proteins, Small / Q000096:biosynthesis* / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D000098:Acetophenones; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D050888:Heat-Shock Proteins, Small; C036483:T-DNA; D014157:Transcription Factors; C051667:acetosyringone