Abstract
Agrobacterium tumefaciens infects various plants and causes crown gall diseases involving temporal expression of virulence factors. SghA is a newly identified virulence factor enzymatically releasing salicylic acid from its glucoside conjugate and controlling plant tumor development. Here, we report the structural basis of SghR, a LacI-type transcription factor highly conserved in Rhizobiaceae family, regulating the expression of SghA and involved in tumorigenesis. We identified and characterized the binding site of SghR on the promoter region of sghA and then determined the crystal structures of apo-SghR, SghR complexed with its operator DNA, and ligand sucrose, respectively. These results provide detailed insights into how SghR recognizes its cognate DNA and shed a mechanistic light on how sucrose attenuates the affinity of SghR with DNA to modulate the expression of SghA. Given the important role of SghR in mediating the signaling cross-talk during Agrobacterium infection, our results pave the way for structure-based inducer analog design, which has potential applications for agricultural industry.
Highlights
Regulation of gene transcription is essential for bacteria to maintain their cellular function and respond to environmental changes
We found that the accumulated sucrose at the wound sites during healing appears to serve as an environmental stimulus involved in the SghR-SghA pair mediating the signaling cross-talk at the late stage of Agrobacterium infection [7]
To further reveal that SghA is regulated by SghR and that this pair, SghR-SghA, is involved in regulating plant tumor development, we examined the tumor occurrence and growth on carrot disks that are infected by either WT or deletion mutant Agrobacterium strains (DsghA, DsghR, and DsghRA)
Summary
Regulation of gene transcription is essential for bacteria to maintain their cellular function and respond to environmental changes. In addition to the C-terminal core domain and the hinge helix, hydrogen bonds formed between Arg19 in the N-terminal DBD and Thr1339 in the N-subdomain contribute to the dimerization of SghR in our complex (see Fig. 6C).
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