Cyclic di-GMP interact with putrescine via a PilZ domain receptor YcgR

The cell motility is one of the key pathogenic factors that contribute to the virulence of Dickeya oryzea, which is a prevalent bacterial pathogen capable of infecting a range of crops and plants. We showed recently that the bacterial second messenger c-di-GMP, and the putrescine-mediated quorum sensing (QS) system, are both involved in the regulation of the bacterial motility in D. oryzea EC1. In this study, we set to determine whether and how there two signaling mechanisms work together to modulate the bacterial motility. The results showed that the second messenger signaling system interacts with the putrescine QS system via the c-di-GMP receptor YcgR, which could promote the activity of SpeA, the rate-limiting enzyme in the putrescine biosynthesis pathway, thereby increasing the intracellular putrescine levels. However, it was shown that this facilitative effect could be inhibited by c-di-GMP molecules. In addition, we demonstrated the dominance of c-di-GMP over putrescine in the regulation of bacterial motility. The findings from this study provide the first insight into the interaction between c-di-GMP and putrescine in bacteria and provide a valuable reference for the study of intracellular second messenger system and polyamine-mediated quorum sensing system in other bacteria. ImportanceDickea oryzea is a major bacterial pathogen capable of infesting many plants and crops, causing significant economic damage to rice and banana production especially. Bacterial motility is a key pathogenic factor of D. oryzea to compete for food resources and infect their host species, which is negatively regulated by c-di-GMP and positively regulated by putrescine, respectively. However, the connection between c-di-GMP and putrscine in regulating the motility of D.oryzea is not understood. Here we revealed the link and the mechanism of interaction between them, showing that c-di-GMP interact with putrescine via a receptor of c-di-GMP. The significance of our research is in providing the first insight into the interaction between c-di-GMP and putrescine and the methods and experimental designs in our study will provide a valuable reference for subsequent studies on the link between c-di-GMP and putrescine in other bacteria and even the regulatory mechanisms of complex bacterial motility networks, respectively.