A new model for virulence in the emerging Gram-positive phytopathogen, Rhodococcus fascians
E. SAVORY (1), A. Creason (1), S. Fuller (1), D. Stevens (1), J. Chang (1) (1) Oregon State University, U.S.A.

Rhodococcus fascians is a Gram-positive phytopathogenic bacteria of emerging importance that causes abnormal growths such as leafy galls or witch’s brooms on a wide range of plants. Disease attributed to R. fascians has been an increasing problem for wholesale and nursery growers in the United States. Diseased plants are unmarketable leading to significant economic losses for the nursery industry. The extant model predicts that R. fascians synthesizes a mixture of the plant hormone, cytokinin, to disrupt host homeostasis and induce shoot proliferation. Virulence is linked to three loci, att, fasR, and fas, which are found on a linear plasmid in most pathogenic strains of R. fascians. We have generated mutants with non-polar deletions, as well as complemented and overexpression strains in genes previously described as necessary for virulence. Our results suggest that fasR encoding a putative transcription factor and fasD encoding an isopententyltransferase are the genes that affect virulence. The others, fasA, fasB, fasE, and fasF are not necessary. Additionally, we previously reported on a pathogenic strain that lacks the linear plasmid but encodes att, fasR, and a gene encoding two domains of FasD and FasF. Together, our data are inconsistent with the extant model and new models for the role of microbial-synthesized cytokinins in pathogenicity of plants will be described.

Abstract Number: C21-5, P19-711
Session Type: Concurrent