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SUMMARY Carotenoids perform a broad range of important functions in humans; therefore, carotenoid biofortification of maize (Zea maysL.), 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 ofPTOXin carotenoid biosynthesis in maize has not yet been explored. In this study, we characterized the maizePTOXlocus by forward‐ and reverse‐genetic analyses. While most higher plant species possess a single copy of thePTOXgene, 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 thePTOXgenes as being causal of the classic maize mutant,albescent1. Remarkably, overexpression ofZmPTOX1significantly improved the content of carotenoids, especially β‐carotene (provitamin A), which was increased by ~threefold, in maize kernels. Overall, our study shows that maizePTOXlocus 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. 

Summary Herbivore‐induced plant volatiles act as danger signals to prime defense responses in neighboring plants, yet in many cases the mechanism behind this priming is not known. Volatile signals may be recognized directly by receptors and/or converted into other active compounds. Here we investigate the metabolic fate of volatile indole, a known priming signal in maize (Zea mays), to determine if its conversion to other compounds could play a role in its priming of defenses.We identified benzoxazinoids as major products from volatile indole using heavy isotope‐labeled volatile indole and Pathway of Origin Determination in Untargeted Metabolomics (PODIUM) analysis. We then used benzoxazinoid biosynthesis maize mutants to investigate their role in indole‐mediated priming.Labeled volatile indole was converted into DIMBOA‐glucoside in abx2(benzoxazinone synthesis2)‐dependent manner. Thebx2mutant plants showed elevated green leaf volatile (GLV) production in response to wounding andSpodoptera frugiperdaregurgitant irrespective of indole exposure.Thus, volatile indole is converted into benzoxazinoids, and part of its priming mechanism may be due to the enhanced production of these phytoanticipins. However, indole‐mediated enhanced GLV production does not rely on the conversion of indole to benzoxazinoids, so indole also has other signaling functions. 

SUMMARY Zea mays(maize) makes phytoalexins such as sesquiterpenoid zealexins, to combat invading pathogens. Zealexins are produced from farnesyl diphosphate in microgram per gram fresh weight quantities. As farnesyl diphosphate is also a precursor for many compounds essential for plant growth, the question arises as to howZ. maysproduces high levels of zealexins without negatively affecting vital plant systems. To examine if specific pools of farnesyl diphosphate are made for zealexin synthesis we made CRISPR/Cas9 knockouts of each of the three farnesyl diphosphate synthases (FPS) inZ. maysand examined the resultant impacts on different farnesyl diphosphate‐derived metabolites. We found that FPS3 (GRMZM2G098569) produced most of the farnesyl diphosphate for zealexins, while FPS1 (GRMZM2G168681) made most of the farnesyl diphosphate for the vital respiratory co‐factor ubiquinone. Indeed,fps1mutants had strong developmental phenotypes such as reduced stature and development of chlorosis. The replication and evolution of thefpsgene family inZ. maysenabled it to produce dedicated FPSs for developmentally related ubiquinone production (FPS1) or defense‐related zealexin production (FPS3). This partitioning of farnesyl diphosphate production between growth and defense could contribute to the ability ofZ. maysto produce high levels of phytoalexins without negatively impacting its growth.