A novel genetic functional unit related with stress-response oligosaccharides

GIORGI M. E; KOLMAN M. A.; GIARROCO L. G; SALERNO G. L

Parana

Simposio; LIV Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2018

SAIB

The accumulation of compatible solutes is one of the physiological responses for abiotic stress adaptation of cyanobacteria. Those are low-molecular mass solutes that do not interfere with cell metabolism. In filamentous-heterocystic cyanobacteria, in addition to sucrose we have previously described the synthesis of sucroglucans (polymer series derived from sucrose) in response to salt stress and elucidated the structures. In the present study we analyzed the phenotype of Nostoc mutants in an orf with high similarity with the sucrose synthase gene, and the occurrence of sucrose and sucroglucans in cells subjected to abiotic stresses (e.g. desiccation, high temperature, and salt). Less stress tolerance was shown in cells of mutants lacking the protein product of that orf, which paralleled the absence of oligosaccharide accumulation. Surprisingly, our results revealed a polar effect in one of the mutants that could involve an adjacent gene in the synthesis of the oligosaccharides. RT-PCR analyses revealed that both genes increased their expression under stress treatments. Subsequently, we investigated the presence of this gene arrangement (putative operon) in different cyanobacterial genomes, concluding that it was restricted to filamentous strains belonging to Nostocales and Stigonematales. The two orfs were expressed in Escherichia coli for functional characterization, as part of the elucidation of the metabolic pathway leading to the oligosaccharide biosynthesis in Nostoc sp.