Mutagenesis of the enolase-phosphatase gene in Xanthomonas oryzae pv. oryzae affects growth on methylthioadenosine and in vivo S-adenosylmethionine pools.

Enolase-phosphatase (E1), as an enzyme, is involved in methionine salvage pathway in many prokaryotic and eukaryotic organisms. But the identity and function of E1 in Xanthomonas oryzae pv. oryzae (Xoo) remain undetermined. Here, we report the cloning and characterization of E1 gene, named xep, from Xoo. Sequence analysis shows that XEP is highly conserved among the six Xoo strains we investigated and all other Xanthomonas species. The strain with an insertion mutation in xep could not grow when methylthioadenosine (MTA) was used as the sole sulfur source, but its growth in rice leaves was comparable to that of wild-type strain. Furthermore, the mutant also showed less S-adenosylmethionine (SAM) and lower gene expression of sulfate reduction gene raxQ, compared to wild-type bacterial cells. Introduction of wild-type xep gene to the mutant resulted in the full restoration of growth on MTA, the SAM quantity and the expression level of raxQ. The results demonstrate that xep is involved in the predicted methionine salvage pathway and an inactive form of this gene results in a decreased SAM level in vivo. Our data also indicate that SAM may play a role in the regulation of sulfur reduction at the transcriptional level in Xoo.