Effect of phytohormones from different classes on gene expression of Chlorella sorokiniana under nitrogen limitation for enhanced biomass and lipid production

Recently, the use of phytohormones has been found to be expedient for improving biomass and lipid productivity for algal biofuel production. The comparative effect of phytohormones from different classes on biomass and lipid productivity, and the expression of the related genes under nitrogen-limitation is not yet explored. In the present study, the optimized concentrations of different phytohormones, auxin - indole acetic acid (IAA), gibberellin - gibberellic acid (GA) and cytokinin - kinetin (K) showed 45.55%, 35.94% and 37.37% increase in biomass productivity in Chlorella sorokiniana as compared to nitrogen-limited control (ON) respectively. The highest biomass productivity of 146.07 mg L(-1)d(-1) and relative rbcL gene expression was observed in IAA (7.5 mg L-1) supplemented treatment. However, K (10 mg L-1) supplementation under N-limitation showed highest lipid content of 35.85% and accD gene expression as compared to other treatments. Overall, highest lipid productivities of 50.24 and 49.43 mg L(-1)d(-1) were observed in optimized IAA and K supplemented treatments respectively. Findings from the present study illustrated the differential response of phytohormones from different classes on biomass and lipid enhancement, fatty acid composition and expression of related genes. These novel findings could be advantageous for the development of promising strategies for improving microalgal biomass and lipid productivity using phytohormones for sustainable biofuel production.