PSY is a rate-limiting enzyme in carotenoid biosynthesis pathway in maize (Zea mays) leaves

Aim and Carotenoids are one of the most abundant pigments in nature and an essential compound of photosynthesis apparatus. In addition, carotenoids play a significant role in human and animal diet, because they are precursors for vitamin A and act as antioxidants. Thus, increasing carotenoid levels in plants, especially cereals as the main food for human and animals, could have a dramatic impact on improving plant yield and nutritional value. Among several enzymes involved in carotenoid biosynthesis pathway, PSY has been known as a key enzyme. So far, three PSY genes have been identified in maize; however, all related enzymes do not show similar activity in all tissues. Considering existing of three PSY genes, whether over-expression of this enzyme can still increase carotenoid biosynthesis levels in maize, is largely unknown. Tissue culture and transformation was carried out using the method developed by Ahmadabadi et al. (1). Total DNA was extracted from maize leaves according to Doyle&Doyle method (5). To confirm transgene presence in regenerated transgenic plants, PCR reaction was performed using specific primers. Pigment content of transgenic plants was analyzed by HPLC method. In this study, through expression of a foreign PSY gene in maize, we showed that maize include a high potential to increase carotenoid levels via over-expression of PSY, and thus, the PSY gene is a rate-limiting enzyme in carotenoid biosynthesis pathway in maize. It should be mentioned that transgenic plants were similar to wild-type plants in terms of growth, development and yield, while the general carotenoid levels was significantly increased. In particle, the level of beta-carotene as a precursor of vitamin A was improved considerably. Our results show that maize has a high potential for increasing carotenoid levels, especially beta-carotene, that can have a significant role in maize breeding programs in order to improve its nutritional value without any negative effect on yield quantity.