Developmental order of upper floral meristem (UFM) and lower floral meristem (LFM) contribute to inflorescence architecture and kernel orientations in maize

he developmental plasticity of inflorescence in maize depends on meristems, which are highly regulated structures that directly affect reproductive potential and yield. Although mutations of inflorescence meristem (IM) and spikelet meristem (SM) had been reported to affect inflorescence in maize, whether and how upper floral meristem (UFM) and lower floral meristem (LFM) affect inflorescence and kernel development is largely unknown. Here, we characterized the reversed kernel1(rk1) mutant that displays reveals kernels with giant embryos but normal vegetative growth, compared to its wild type (WT). The grain crude protein and crude fat in rk1 were significantly higher than that in WT. The mutant phenotype of rk1 in the ear only occurs when rk1 is transmitted through the female. Histocytology demonstrated that developmental order of UFM and LFM of rk1 was reversed, UFM differentiation was inhibited while LFM differentiation was initiated in rk1. Transcriptome analysis also showed that differential gene expression in rk1 was strongly related to multiple biological processes, especially cell differentiation, organ development, hormone response and carbohydrate metabolism. The homeostasis of auxin (IAA), gibberellins (GA), cytokinin (CTK), and abscisic acid (ABA) varied in the inflorescence differentiation stage in rk1, and immunohistochemistry also showed that the localization signals for IAA, GA, CTK, and ABA significant difference in the pistillate inflorescence developmental stage. In this study, it is a novel discovery that developmental order of UFM and LFM can contribute to produced reversed kernels with giant embryos. The results of this study provide novel insights into maize inflorescence development.