Regulation of carotene biosynthesis through expression of phytoene desaturase gene in Chlamydomonas reinhardtii grown under high light intensity

External phytoene desaturase genes from Arabidopsis (PDS1, AT1G0670.1) and (TP/PDS1 AT4G14210.1) were cloned in PFGC5941 vectors and successfully transformed to Chlamydomonas renhardtii independently via Agrobacterium tumefaciens. TAP medium and basta sensitivity test as a biomarker were suitable for differentiation between the transformed cells and non-transformed one. The result of transformation manifest that the transformed cells resisted basta up to 30 mu g/ml (sub lethal dose) whereas the wild able to grow at 10 mu g/ml only. The transformed colonies were scaled up into liquid TAP media for 8 days and the expression of these colonies confirmed using PCR amplification for PDS1 and TP/PDS1 genes with specific primers. Further the functionality of the inserted desaturase genes was confirmed by restriction enzymes of cloned vectors with Nco1and BamH1. qRT-PCR of most cell lines resists the basta resulted in that the level of PDS1 expression ranged between (2.28-3.26) and for TP/PDS1 (2.62-3.54) under normal light intensity (80 mu mol photon m(-2) s(-1)). Further, the functionality of the inserted desaturase genes was confirmed by the metabolic analysis of transformed cultures grown under high light intensity (100-180 pmol photon m(-2) s(-1)). The elevating of the biosynthesis and accumulation of carotene as a result of light intensity gave good evidence that phytoene desaturase play a role for protection of the plastids from high intensity of light. Not only the elevating in carotene biosynthesis but also the expressions reached 8 and 19 folds for both PDS1 and TP/PDS1 with respect to wild cell at the high light intensity (180 mu mol photon m(-2) s(-1)). Such results indicate that the functionality of TP/PDS1 may be light dependent. The positive correlation between the expression of PDS and carotene synthesis (quality and quantity) suggesting differential regulation between the nature of genes and abiotic stress. Also, the functionality of gene expression under high exposure intensity suggested the priority of TP/PDS1 to be over expressed rather than the PDS1 in cytosol and it plays a role as an auto protective against the stress factor.