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POSTERS: Molecular plant-microbe interactions

small RNA rprA modulates the pathogenesis of Erwinia amylovora
Jingyu Peng - Michigan State University. George Sundin- Michigan State University

Fire blight, caused by Erwinia amylovora, is a devastating disease infecting many rosaceous plants, such as apple and pear. E. amylovora initiates the infection through migration from nectarthodes of host floral cups to xylem vessels. Formation of biofilms within xylem vessels blocks water transport and cause wilting of a host. E. amylovora cells that detach from biofilms are translocated and cause infections in the new site. A previous study of the RNA chaperone protein Hfq in E. amylovora yielded the identification of a small RNA rprA, which contributes to the pathogenesis of E. amylovora on both immature pear fruits and apple shoots, respectively. In this study, we demonstrate that rprA positively regulates two critical virulence factors of E. amylovora: amylovoran, the main exopolysaccharide in E. amylovora, and HrpS, the global regulator of type III secretion system in E. amylovora. Interestingly, we also found that rprA acted as a negative modulator of levansucrase activity, cellulose production and motility of E. amylovora, which function synergically in biofilm formation of E. amylovora cells. In view of these results, we further showed the positive involvement of rprA in coordinating dispersal events of biofilm cells in an in vitro assay. Ongoing research related to the in vivo visualization of the rprA-mediated dispersal movement of biofilm in E. amylovora will be discussed. Taken together, our results shed light on a better understanding of the decision-making process of E. amylovora in transitions from biofilm to planktonic modes of growth within a host.