title: Succinic Semialdehyde Promotes Prosurvival Capability of Agrobacterium tumefaciens.
abstract: Succinic semialdehyde (SSA), an important metabolite of γ-aminobutyric acid (GABA), is a ligand of the repressor AttJ regulating the expression of the attJ-attKLM gene cluster in the plant pathogen Agrobacterium tumefaciens. While the response of A. tumefaciens to GABA and the function of attKLM have been extensively studied, genetic and physiological responses of A. tumefaciens to SSA remain unknown. In combination with microarray and genetic approaches, this study sets out to explore new roles of the SSA-AttJKLM regulatory mechanism during bacterial infection. The results showed that SSA plays a key role in regulation of several bacterial activities, including C4-dicarboxylate utilization, nitrate assimilation, and resistance to oxidative stress. Interestingly, while the SSA relies heavily on the functional AttKLM in mediating nitrate assimilation and oxidative stress resistance, the compound could regulate utilization of C4-dicarboxylates independent of AttJKLM. We further provide evidence that SSA controls C4-dicarboxylate utilization through induction of an SSA importer and that disruption of attKLM attenuates the tumorigenicity of A. tumefaciens. Taken together, these findings indicate that SSA could be a potent plant signal which, together with AttKLM, plays a vital role in promoting the bacterial prosurvival abilities during infection.
  
  
  OBJECTIVE
  Agrobacterium tumefaciens is a plant pathogen causing crown gall diseases and has been well known as a powerful tool for plant genetic engineering. During the long history of microbe-host interaction, A. tumefaciens has evolved the capabilities of recognition and response to plant-derived chemical metabolites. Succinic semialdehyde (SSA) is one such metabolite. Previous results have demonstrated that SSA functions to activate a quorum-quenching mechanism and thus to decrease the level of quorum-sensing signals, thereby avoiding the elicitation of a plant defense. Here, we studied the effect of SSA on gene expression at a genome-wide level and reported that SSA also promotes bacterial survival during infection. These findings provide a new insight on the biological significance of chemical signaling between agrobacteria and plant hosts.
authors.affiliation: Institute of Molecular and Cell Biology, Singapore, Singapore National Cancer Centre Singapore, Singapore, Singapore.
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.affiliation: School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
authors.forename: Desong
authors.initials: D
authors.lastname: Tang
authors.affiliation: Institute of Molecular and Cell Biology, Singapore, Singapore School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
authors.forename: Yong-Gui
authors.initials: YG
authors.lastname: Gao
authors.affiliation: Institute of Molecular and Cell Biology, Singapore, Singapore Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, China lianhui@imcb.a-star.edu.sg.
authors.forename: Lian-Hui
authors.initials: LH
authors.lastname: Zhang
mesh_terms: D016960:Agrobacterium tumefaciens / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D053858:Metabolic Networks and Pathways / Q000235:genetics; D046228:Microarray Analysis; D050296:Microbial Viability / Q000187:drug effects*; D009566:Nitrates / Q000378:metabolism; D009876:Operon; D018384:Oxidative Stress; D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D009566:Nitrates; D005680:gamma-Aminobutyric Acid; C009338:succinic semialdehyde