PARENT SESSION
Posters P2C Carbon and nitrogen interactions. Abstracts (614-616)

Sucrose cleavage and photosynthetic carbon assimilation may be co-regulated by the nitrogen source in anabaena. Leonardo Curatti^*,1, Graciela Salerno¹, ¹ Centro de Investigaciones Biológicas (FIBA), CONICET, Mar del Plata, Buenos Aires, Argentina

ABSTRACT- In higher plants, photosynthetic carbon assimilation and nitrogen metabolism have been shown to be coordinated to prevent uncontrolled competition for energy and carbon skeletons. Different signals regulate the expression of the genes involved in both 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 a whole plant nutrient balance, principally by the carbon/nitrogen status. In this study, we investigate the relationship between sucrose catabolism and nitrogen assimilation with the modulation of the expression of rbcLS (the gene coding for Rubisco) in the filamentous heterocystic cyanobacterium Anabaena sp. Cyanobacteria are oxygenic photosynthetic organisms that metabolize sucrose as higher plants do, and are useful model systems for understanding the evolution of the linkage between carbon and nitrogen metabolism and CO₂ fixation. In this report we show that in Anabaena sp. PCC 7120 cells, the expression of both susA (the gene coding for sucrose synthase, responsible for sucrose cleavage in vivo) and rbcLS was stimulated by ammonium. The sequence of an ammonium-responsive promoter of susA was determined and presented high sequence identity to the ammonium-regulated promoter of rbcLS, suggesting a co-regulation between sucrose metabolism and carbon fixation in response to the nitrogen source. Also, the activity of the rbcLS promoter was stimulated in cells of an Anabaena mutant strain that over-expresses susA and accumulates lower levels of sucrose. Taken together, these data suggest that in Anabaena, sucrose metabolism, carbon fixation and nitrogen assimilation may be co-regulated through the transcriptional control of key genes of these pathways. Supported by CONICET, ANPCyT, FIBA and UNMdP.

KEY WORDS: Anabaena, sucrose, carbon, assimilation