Poster: Photosynthesis

Abs # 338: Carbon and nitrogen assimilation and photosynyhesis in Anabaena sp.

Presenter:	Salerno, Graciela L, fibamdq@infovia.com.ar
Authors	Salerno, Graciela L (A)   Curatti, Leonardo  (A)
Affiliations:	(A): Fundacion para Inves Biol Ap

In higher plants, nitrogen assimilation, carbohydrate production and CO₂ assimilation have been shown to be coordinated and regulated to prevent uncontrolled competition for energy and carbon skeletons. Different signals regulate the expression of genes involved in those metabolisms. Thus, a close interaction between carbon and nitrogen signaling was shown to regulate Rubisco levels. Recent data suggest that photosynthesis responds to and is controlled by whole plant nutrient balance, principally by the carbon to nitrogen status. In this study, we investigate the relationship between sucrose metabolism and nitrogen assimilation with the modulation of the expression of rbcLS (encoding for Rubisco) in the filamentous heterocystic cyanobacterium Anabaena sp., a model system that could be useful in understanding how could have evolved the linkage between carbon and nitrogen metabolism and CO₂ fixation. Cyanobacteria metabolize sucrose essentially as higher plants do. The expression of susA (encoding for sucrose synthase, responsible of sucrose cleavage in vivo), susB, and rbcLS is stimulated by ammonium in cells of Anabaena sp. PCC 7120. Both susA and susB promoters were shown to be upregulated by ammonium and to share a high sequence similarity with the rbcLS promoter, suggesting a co-regulation of sucrose metabolism and carbon fixation genes in response to the nitrogen source. The activity of the rbcLS promoter is modulated by sucrose, either exogenously supplied or in Anabaena mutants that produce different levels of sucrose. Taken together, these data suggest that sucrose levels, and particularly sucrose cleavage in Anabaena, are involved in the interaction between carbon and nitrogen metabolism and photosynthesis.