ARS | Publication request: Natural variation in the sequence of PSY1 enhances provitamin A biofortification of yellow maize

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 2012
Publication Date: December 17, 2012
Citation: Fu, Z., Chai, Y., Zhou, Y., Yang, X., Warburton, M.L., Xu, S., Cai, Y., Zhang, D., Li, J., Yan, J. 2012. Natural variation in the sequence of PSY1 and frequency of favorable polymorphisms among tropical and temperate maize germplasm. Theoretical and Applied Genetics. doi:10.1007/s00122-012-2026-0.

Interpretive Summary: Provitamin A (Pro-VA) is converted to Vitamin A in the human body, and is necessary for human vision and immune system health, especially in growing children. The metabolic pathway in plants that creates Pro-VA is the carotenoid synthesis pathway, and all steps and enzymes in the process have been identified. In maize, some enzymes are more important in the production of high levels of Pro-VA than others, and identifying these has been an important goal in order to breed for very high Pro-VA lines. High Pro-VA lines created quickly and efficiently via marker assisted selection would allow for varieties to be grown by farmers as quickly as possible, thus reducing the health and mortality problems caused by a lack of Pro-VA in the developing world. In this article, we identify the DNA sequence variation from three important genes in the pathway and determine the best possible combination of alleles (genetic differences between different maize individuals) that leads to optimum levels of Pro-VA in a single maize line. We also present markers and strategies to create these high Pro-VA lines as quickly and efficiently as possible.

Technical Abstract: Provitamin A (Pro-VA) is necessary for human vision and immune system health, especially in growing children. The first committed step in the maize carotenoid biosynthesis pathway starts with the PSY1 (phytoene synthase 1) gene, which controls flux of substrates into the pathway. A model of the carotenoid pathway that would theoretically achieve the highest levels of Pro-VA would involve shunting high levels of substrates into the pathway, and then shifting the flow of these substrates towards the branch of the pathway leading to the production of zeaxanthin (the step controlled by the lcye gene) but stopping flow at the step that accumulates ß-carotene and not allowing it to be converted to the next metabolite (the step controlled by the crtRB1 gene). In this study, PSY1 was subjected to association mapping in two diverse maize populations, QTL mapping in one segregating population, and expression analysis of lines polymorphic for sites within PSY1. Results suggest that a 378 Insertion/Deletion (InDel) upstream of the transcription start site and a single nucleotide polymorphism (SNP) (SNP7) in the fifth exon.