Loss-of-function mutation of Plastid Terminal Oxidase (ZmPTOX) cause zebra leaf and white kernel by affecting plastid development in maize
Zebra leaf is a special phenotype of variegated leaf in monocotyledonous plant. Here, we characterized a mutant zebra10 (zb10) in maize, which displays defective chloroplast development in white section of leaves at the seedling stage and pale-white kernels. Map based cloning revealed that ZB10 encodes plastid terminal oxidase (ZmPTOX) which is localized in chloroplasts. ZmPTOX protein is highest expressed in leaves and also highly expressed in endosperm. Expression and metabolism analysis showed that function-loss of PTOX interferes with carotenoid synthesis and chloroplast biogenesis by affecting phytoene desaturase activity. In-depth observation showed that crossband formation of zebra leaf could be related to photoperiodic rhythm, and expression of alternative oxidases 2 (ZmAOX2) could be regulated by circadian rhythm and light intensity in zb10. Further studies revealed ectopic expression of ZmAOX2 protein can function in chloroplasts and rescue the defective phenotype of im. We conclude that ZmPTOX plays an vital role in carotenoid synthesis and plastid biogenesis in maize. ZmAOX2 involve in formation of zebra crossbands with diurnal rhythm and green-revertible process of leaves in zb10. Overall design: Leaves of WT and zb10 at 4th-leaf stage [WT_V4, zb10_V4G (green section),  zb10_V4W (white section)] and 9th-leaf stage (WT_V9, zb10_V9) and 16DAP endosperms (WT_16d endo,  zb10_16d endo) were selected for transcriptome sequencing samples (three biological replicates per tissue).  To compare the effect of ZB10 gene mutation on the expression of carotenoid synthesis pathway genes and AOX family genes in maize.