The maize PLASTID TERMINAL OXIDASE (PTOX) locus controls the carotenoid content of kernels.

SUMMARY: Carotenoids perform a broad range of important functions in humans; therefore, carotenoid biofortification of maize (Zea mays L.), one of the most highly produced cereal crops worldwide, would have a global impact on human health. PLASTID TERMINAL OXIDASE (PTOX) genes play an important role in carotenoid metabolism; however, the possible function of PTOX in carotenoid biosynthesis in maize has not yet been explored. In this study, we characterized the maize PTOX locus by forward‐ and reverse‐genetic analyses. While most higher plant species possess a single copy of the PTOX gene, maize carries two tandemly duplicated copies. Characterization of mutants revealed that disruption of either copy resulted in a carotenoid‐deficient phenotype. We identified mutations in the PTOX genes as being causal of the classic maize mutant, albescent1. Remarkably, overexpression of ZmPTOX1 significantly improved the content of carotenoids, especially β‐carotene (provitamin A), which was increased by ~threefold, in maize kernels. Overall, our study shows that maize PTOX locus plays an important role in carotenoid biosynthesis in maize kernels and suggests that fine‐tuning the expression of this gene could improve the nutritional value of cereal grains. Significance Statement: We used a genetic approach to show that an important enzyme PLASTID TERMINAL OXIDASE (PTOX) regulates the biosynthesis of carotenoids, a pivotal nutrient for human health, in maize kernels. This work provides the first evidence that PTOX plays an important role in carotenoid biosynthesis in cereal grains, and we successfully increased the nutrient value of maize by overexpressing this gene. [ABSTRACT FROM AUTHOR]