Contribution of the cold shock protein CspA to virulence in Xanthomonas oryzae pv. oryzae.

Xanthomonas oryzae pv. oryzae (Xoo) causes a damaging bacterial leaf blight disease in rice. Cold shock proteins (Csps) are highly conserved nucleic acid-binding proteins present in various bacterial genera， but relatively little is known about their functions in Xanthomonas. Herein， we identified four Csps (CspA-CspD) in the Xoo PXO99 strain. Deletion of cspA decreased cold adaptation and a few known pathogenic factors， including bacterial pathogenicity， biofilm formation and polysaccharide production. Furthermore， we performed transcriptomic and chromosome immunoprecipitation (ChIP) experiments to identify direct targets of CspA and to determine its DNA-binding sequence. Integrative data analysis revealed that CspA directly regulates two genes， PXO_RS11830 and PXO_RS01060， by binding to a conserved CCAAT sequence in the promoter region. We generated single-deletion mutants of each gene and the results indicate that both are responsible for Xanthomonas pathogenicity. In addition， quantitative real-time polymerase chain reaction and western blotting showed that CspA suppressed the expression of its direct targets. In summary， our study clarifies the characteristics of Csps in Xanthomonas and greatly advances our understanding of the mechanisms underlying the contribution of CspA to bacterial virulence.