Chatterjee 9728505 Erwinia carotovora subspecies carotovora (Ecc), a gram-negative bacterial plant pathogen, produces various extracellular enzymes (= exoenzymes) such as pectate lyase (Pel), polygalacturonase (Peh), pecin lyase (Pnl), cellulase (Cel) and protease (Prt) as well as HarpinEcc, an elicitor of the hypersensitive reaction. A long term goal of this research is to elucidate the genetic and molecular mechanisms that, by controlling the production of such exoenzymes and HarpinEcc, affect the outcome of bacterial plant interactions. Based upon recent findings with Ecc strain 71, it is thought that rsmA, aepH and kdgR specify the key components of a regulatory circuit which controls the production of exoenzymes, HarpinEcc and secondary metabolites as well as the cell density (quorum) sensing signal, N-acyl-L-homoserine lactone (AHL). The current model for regulation postulates the following events: RsmA (Regulator of secondary metabolism), a RNA-binding protein, promotes message decay. KdgR (repressor of genes for Pel as well as pectate catabolism) binds aepH (activator of exoenzyme and secondary metabolite production) DNA and negatively controls aepH RNA levels. In the absence of aepH RNA, RsmA remains fully active, promoting message decay. As the level of active KdgR drops, aepH transcription is stimulated, producing a 479 base RNA species which bind RsmA, thereby depleting the pool of free RsmA. The formation of RsmA:aepH RNA complex creates a favorable ribonucleoprotein conformation that facilitates RNA processing. AepH' RNA, the 259 base processed product, negatively controls RsmA levels by affecting translation or turnover of RsmA. Thus, aepH' RNA is postulated to primarily act via RsmA. The major thrust of this project is to produce fundamental knowledge of this novel regulatory system controlling exoenzyme production. The specific objectives are to: examine the effects of RsmA on transcripts of exoenzyme genes and their regulator genes; elucidate the role of KdgR i n aepH expression; examine processing of aepH RNA; and elucidate the role of the processed aepH' RNA on RsmA production. Since RsmA and aepH play pivotal roles in the production of exoenzymes and secondary metabolites (i.e., antibiotics, pigments, polysaccharides) in several other bacteria, this research has broad ramifications. From a practical perspective, the emerging knowledge could be exploited to manipulate the levels of bacterial products useful in various biotechnological applications, including biological control of plant diseases.
