SYMBIOTIC IMPLICATIONS OF TYPE-III PROTEIN SECRETION MACHINERY IN RHIZOBIUM

The symbiotic plasmid of Rhizobium sp. NGR234 carries a cluster of gen es that encodes components of a bacterial type III secretion system (T TSS). In both animal and plant pathogens, the TTSS is an essential com ponent of pathogenicity. Here, we show that secretion of at least two proteins (y4xL and NolX) is controlled by the TTSS of NGR234 and occur s after the induction with flavonoids. Polar mutations in two TTSS gen es, rhcN and the nod-box controlled regulator of transcription y4xl, b lock the secretion of both proteins and strongly affect the ability of NGR234 to nodulate a variety of tropical legumes including Pachyrhizu s tuberosus and Tephrosia vogelii.