The Sinorhizobium meliloti SyrM regulon: effects on global gene expression are mediated by syrA and nodD3 (SyrA)

We characterized transcriptomes of a strain overexpressing syrA. Our work shows that the syrA transcriptome shares similar gene expression changes to the syrM and nodD3 transcriptomes and that nodD3 and syrA may be the only targets directly activated by SyrM. We propose that most of the gene expression changes observed when nodD3 is overexpressed are due to NodD3 activation of syrM expression, which in turn stimulates SyrM activation of syrA expression. The subsequent increase in SyrA abundance alters activity of the ChvI-ExoS-ExoR circuit, resulting in broad changes in gene expression. Gene expression profiling of Sinorhizobium meliloti overexpressing syrA was performed using custom Affymetrix GeneChips