Comparison of gene expression patterns of Kappaphycus alvarezii (Rhodophyta, Solieriaceae) under different light wavelengths and CO2 enrichment

Abstract

Transcriptomes associated with the process of photosynthesis and carbon fixation have offered insights into the mechanism of gene regulation in terrestrial plants, however limited information is available as far as macroalgae are concerned. Intertidal red alga, Kappaphycus alvarezii is exposed to different wavelengths of light in their lives as light quantity and quality changes at different depths in seawater. This investigation aims to study the underlying mechanisms associated with photosynthesis and carbon fixation under specific light qualities and CO2 enrichment. Light regulation of gene expression has not been previously described for red algae. By using next generation sequencing, transcriptome profiling of K. alvarezii generated 76,871 qualified transcripts with a mean length of 979bp and a N50 length of 1,707bp and 55.83% transcripts were annotated on the basis of function. Blue, green and red light all have demonstrated roles in modulating light responses, such as changes in gene expression. Here we analysed the effects of light regulation on four selected photosynthesis aspects (light-harvesting complex, phycobilisomes, photosystems and photoreceptors). We observed that light-regulated gene expression in this species is not a single light response and different light qualities are transduced to regulate the same metabolic pattern. The carbon fixation pathway was analysed and key genes encoding enzymes involved in the carbon fixation pathway such as ppc, pepc, prk, pgk, ppdk, provided that unequivocal molecular evidence that most of the C3 and C4 pathway genes were actively transcribed in K. alvarezii. In addition to this the CO2 induced transcriptome suggested the possibility of shifting carbon metabolism pathway after acclimation to increased level of CO2. Impact of CO2 enrichment on the cultures has provided new insight into the response to rising CO2.