Inhibition of grape crown gall by agrobacterium vitis f2/5 requires two nonribosomal peptide synthetases and one polyketide synthase

Abstract

Agrobacterium vitis nontumorigenic strain F2/5 is able to inhibit crown gall disease on grapevines. The mechanism of grape tumor inhibition (GTI) by F2/5 has not been fully determined. In this study, we demonstrate that two nonribosomal peptide synthetase (NRPS) genes (F-Avi3342 and F-Avi5730) and one polyketide synthase gene (F-Avi4330) are required for GTI. Knockout of any one of them resulted in F/25 losing GTI capacity. We previously reported that F-Avi3342 and F-Avi4330 but not F-Avi5730 are required for induction of grape tissue necrosis and tobacco hypersensitive response. F-Avi5730 is predicted to encode a single modular NRPS. It is located in a cluster that is homologous to the siderophore vicibactin biosynthesis locus in Rhizobium species. Individual disruption of F-Avi5730 and two immediate downstream genes, F-Avi5731 and F-Avi5732, all resulted in reduced siderophore production; however, only F-Avi5730 was found to be required for GTI. Complemented F-Avi5730 mutant (DF-Avi5730+) restored a wild-type level of GTI activity. It was determined that, over time, populations of DF-Avi4330, DF-Avi3342, and DF-Avi5730 at inoculated wound sites on grapevine did not differ from those of DF-Avi5730+ indicating that loss of GTI was not due to reduced colonization of wound sites by mutants.