The lemA gene required for pathogenicity of Pseudomonas syringae pv. syringae on bean is a member of a family of two-component regulators

Abstract

The lemA gene of the plant pathogen Pseudomonas syringae pv. syringae is required for disease lesion formation on bean plants. Cosmid clones that complemented a lemA mutant in trans were isolated previously. The lemA gene was localized by subcloning and transposon mutagenesis. The lemA region and flanking DNA were sequenced, and an open reading frame of 2.7 kb was identified. The nucleotide and predicted amino acid sequences of the lemA gene showed sequence similarity to a family of prokaryotic two-component regulatory proteins. Unlike most of the previously described two-component systems, the lemA gene product contained homology to both components in one protein. Mutations introduced upstream and downstream of the lemA gene failed to locate a gene for a second protein component but identified the putative cysM gene of P. syringae pv. syringae. The cysM gene was located upstream of the lemA gene and was divergently transcribed. The lemA gene product was expressed at low levels in P. syringae pv. syringae and appeared to be positively auto-regulated.