Location: Emerging Pests and Pathogens ResearchTitle: Pseudomonas syringae pv. tomato DC3000 CmaL (PSPTO4723), a DUF1330 family member, is needed to produce L-allo-isoleucine, a precursor for the phytotoxin coronatine Author
Submitted to: Journal of Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2013
Publication Date: 1/31/2013
Citation: Worley, J.N., Russell, A.B., Wexler, A.G., Bronstein, P., Kvitko, B.H., Krasnoff, S., Munkvold, K.R., Swingle, B.M., Gibson, D.M., Collmer, A. 2013. Pseudomonas syringae pv. tomato DC3000 CmaL (PSPTO4723), a DUF1330 family member, is needed to produce L-allo-isoleucine, a precursor for the phytotoxin coronatine. Journal of Bacteriology. 195(2):287-296. Interpretive Summary: Many bacteria that cause diseases in plants have the ability to produce toxins that help the bacteria grow and cause disease in plants. Some strains of Pseudomonas syringae bacteria make a specific toxin, called coronatine that causes the plant to turn yellow, interferes with the plants immune system and makes pores in the leaves open so that the bacteria can get inside the leaves easier. The bacteria make coronatine toxin out of several smaller parts. The Pseudomonas syringae bacteria have genes that provide the functions needed to make all the parts of coronatine and to assemble those parts to make the complete and perfect toxin. We know most of the genes involved with this process and what most of them do to put coronatine together, except for one gene - cmaL. In this report, we explain experiments that were done to figure out what the cmaL gene is doing. We found that this gene is necessary to make one of the small parts used by the cell to build coronatine. The small part is called L-allo-isoleucine, which is a rare form of an amino acid. Knowing what this gene does is important because if the bacteria don’t have this gene, then they cannot make coronatine. This work helps to complete humankinds understanding of how bacteria cause disease in plants.
Technical Abstract: Pseudomonas syringae pathovar tomato DC3000 produces the phytotoxin coronatine, a major determinant of the leaf chlorosis associated with DC3000 pathogenesis. The DC3000 PSPTO4723 (cmaL) gene is located in a genomic region encoding type III effectors, however it promotes chlorosis in the model plant Nicotiana benthamiana in a manner independent of type III secretion. Coronatine is produced by ligation of two moieties, coronafacic acid (CFA) and coronamic acid (CMA), which are produced by biosynthetic pathways encoded in separate operons. Cross-feeding experiments, performed in N. benthamiana with cfa, cma, and cmaL mutants, implicate CmaL in CMA production. Furthermore, analysis of bacterial supernatants under coronatine-inducing conditions revealed that mutants lacking either the cma operon or cmaL accumulate CFA rather than coronatine, supporting a role for CmaL in the regulation or biosynthesis of CMA. CmaL does not appear to regulate CMA production, as cmaL mutants are unaltered in the expression of proteins with known roles in CMA production. Rather, CmaL is needed for the first step in CMA synthesis, as wild-type levels of coronatine production are restored to a delta cmaL mutant when supplemented with 50 ug/ml L-allo-isoleucine, the starting unit for CMA production. cmaL is found in all other sequenced P. syringae strains with coronatine biosynthesis genes. This characterization of CmaL identifies a critical missing component in coronatine production and provides a foundation for further investigation of a member of the widespread DUF1330 protein family.