Phototropin is a 
blue light receptor, which mediates a variety of blue-light elicited physiological processes in plants and 
algae. In higher plants these processes include 
phototropism, 
chloroplast movement and stomatal opening. In the green alga 
Chlamydomonas reinhardtii, phototropin plays a vital role in progression of the 
sexual life cycle and in the control of the eye spot size and 
light sensitivity Phototropin is also involved in blue-light mediated changes in the synthesis of chlorophylls, carotenoids, 
chlorophyll binding proteins. We compared the 
transcriptome of phototropin knock out (PHOT KO) 
mutant and wild-type parent to analyze differences in 
gene expression in high light grown cultures (500 μmol photons m−2 s−1). Our results indicate the up-regulation of genes involved in photosynthetic 
electron transport chain, carbon fixation pathway, 
starch, lipid, and 
cell cycle control genes. With respect to photosynthetic 
electron transport genes, genes encoding proteins of the 
cytochrome b6f and 
ATP synthase complex were up regulated potentially facilitating 
proton-coupled 
electron transfer. In addition genes involved in limiting steps in the Calvin cycle 
Ribulose-1,5-bisphosphate carboxylase / 
oxygenase (
RuBisCO), Sidoheptulose 1,7 bisphosphatase (SBPase), 
Glyceraldehyde-3-
phosphate dehydrogenase (3PGDH) and that mediate 
cell-
cycle control (CDK) were also up regulated along with 
starch synthase and 
fatty acid biosynthesis genes involved in 
starch and lipid synthesis. In addition, transmission 
electron micrographs show increased accumulation of starch granules in PHOT 
mutant compared to 
wild type, which is consistent with the higher expression of 
starch synthase genes. Collectively, the altered patterns of 
gene expression in the PHOT mutants were associated with a two-fold increase in growth and 
biomass accumulation compared to 
wild type when grown in environmental photobioreactors (Phenometrics) that simulate a pond environment. In conclusion, our studies suggest that phototropin may be a master 
gene regulator that suppresses rapid 
cell growth and promotes gametogenesis and sexual recombination in 
wild type strains.