A GGDEF and EAL domain-containing protein in Pseudomonas syringae pv. actinidiae regulates virulence via its diguanylate cyclase activity

Abstract Kiwifruit bacterial canker (KBC), caused by Pseudomonas syringae pv. actinidiae ( Psa ), poses a severe threat to the global kiwifruit industry, highlighting the urgent need to elucidate its pathogenic mechanisms. Cyclic diguanylate monophosphate (c-di-GMP) is a bacterial second messenger synthesized by GGDEF domain-containing diguanylate cyclases and degraded by EAL or HD-GYP domain-containing phosphodiesterases. In this study, we characterized PSA_2989, a protein containing both GGDEF and EAL domains, hereafter referred to as DcvP ( D iguanylate c yclase regulating v irulence in Psa ). Biochemical assays demonstrated that DcvP exhibits both DGC and PDE activities in vitro, with DGC activity being more prominent in vivo. Deletion of dcvP enhanced the virulence of Psa on kiwifruit leaves. Transcriptomic and RT-qPCR analyses revealed that DcvP suppresses the expression of type III secretion system (T3SS) genes, flagellar biosynthesis genes, and catalase genes, thereby reducing virulence, motility, and oxidative stress tolerance, primarily through its GGDEF domain. Furthermore, under microaerobic conditions, the expression of dcvP was significantly upregulated, accompanied by increased intracellular c-di-GMP levels and repression of T3SS genes. These results identify DcvP as a negative regulator of Psa virulence through DGC activity and also as being involved in the environmental oxygen response. This work provides new insights into the pathogenic mechanisms of Psa and highlights DcvP as a potential target for KBC control.