ROSE elements occur in disparate rhizobia and are functionally interchangeable between species.

ABSTRACT

Expression of at least ten genes in Bradyrhizobium japonicum, seven of which code for small heat shock proteins (sHsps), is under the control of ROSE (repression of heat shock gene expression). This negatively cis-acting DNA element confers temperature control to a sigma(70)-type promoter. Here, we show that ROSE elements are not restricted to B. japonicum but are also present in Bradyrhizobium sp. (Parasponia), Rhizobium sp. strain NGR234 and Mesorhizobium loti. An overall alignment of all ROSE sequences reveals a highly conserved and probably functionally important region towards the 3'-end of the element. Moreover, we provide genetic evidence for the previously proposed presence of multiple sHsps in these organisms. Primer-extension data of five newly identified ROSE-associated operons show that transcription is repressed at low temperatures and induced after a temperature upshift. Translational ROSE-hsp'-'lacZ fusions of Bradyrhizobium sp. (Parasponia) and Rhizobium sp. strain NGR234 integrated into the chromosome of B. japonicum were heat-responsive. The functionality of these heterologous ROSE elements hints at a common regulatory principle conserved in various rhizobia.