Proteomic profiling of Nostoc flagelliforme reveals the common mechanism in promoting polysaccharide production by different light qualities

Different light qualities have been found to effectively promote polysaccharide production of cyanobacteria, to elucidate the underlying mechanism, the effects of four typical light qualities including ultraviolet radiation B (UVB), red light (R), blue light (B), and mixed light (R:B = 7:15) (RB) on polysaccharide production in Nostoc flagelliforme were comprehensively investigated with white fluorescent light as control. In this study, an iTRAQ-based proteomic approach was employed to explore the proteomes of N. flagelliforme, and 126, 177, 208, and 200 differentially expressed proteins were identified in UVB-, R-, B- and RB-treated N. flagelliforme. Functional classification analysis showed that differentially expressed proteins were mainly involved in photosynthesis, antioxidant activity, and carbohydrate metabolism. Analysis of differentially expressed proteins involved in polysaccharide synthesis revealed that different light qualities shared a common mechanism to promote polysaccharide production by altering carbon allocation and increasing carbon flow into sugar nucleotide synthesis pathway. Activity assay of selected enzymes further verified the proteomic analysis. Our results provide novel insights into the molecular mechanisms of light quality affecting polysaccharide production.