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POSTERS: Molecular plant-microbe interactions

Stringent Response Regulators DksA and ppGpp Positively Regulate Virulence and Host Adaptation of Xanthomonas citri
Yanan Zhang - University of florida. Nian Wang- Citrus Research and Education Center, University of Florida

The stringent response is a response of bacteria to nutrition deprivation and other stress conditions. Regulation of this process involves small signal molecule guanoisine pentaphosphate pppGpp, guanosine tetraphosphate ppGpp (collectively referred to ppGpp) and the RNA polymerase-binding transcription factor DksA. Accumulation of ppGpp in bacteria is mediated by the ppGpp synthetase RelA and the bifunctional ppGpp synthase/hydrolase SpoT. Here, we investigated DksA and ppGpp of Xanthomonas citri subsp. citri (Xcc), the causal agent of citrus canker. ?dksA and ?spoT?relA caused reduced virulence and compromised bacterial growth in host plants, indicating that stringent response regulators are required for full virulence of Xcc. To characterize the effect of DksA and ppGpp on gene expression, transcriptome analyses were conducted on ?dksA, ?spoT?relA double mutant and the wild-type strains grown in XVM2 medium. Transcriptome analyses showed that DksA and ppGpp repress the expression of coding genes for tRNAs, ribosome proteins, iron acquisition, flagellar assembly and enhance the expression of coding genes for histidine metabolism, T3SS, T2SS and TonB-dependent transporters. Phenotypically, the ?dksA and ?spoT?relA strains display altered motility, enhanced siderophore production and are unable to cause hypersensitive response on non-host plant. In conclusion, DksA and ppGpp play an important role in virulence, nutrition uptake and host adaptation of Xcc.