Light induces the circadian rhythm and chloroplast development during seedling de-etiolation in maize

Light plays a crucial role in seedling de-etiolation, initiating the circadian rhythm, chloroplast development, and autotrophic establishment in plants. Although de-etiolation has been extensively studied in various plant species, the specific regulatory network involved in the light quality effects on seedling de-etiolation in maize remains largely unknown. In this study, we investigated the universal effects of far-red, red, and blue light irradiation on seedling de-etiolation in two maize inbred lines (B73 and Mo17) and their two hybrid genetic backgrounds (B73xMo17 and Mo17xB73). A sequential increase in the chlorophyll content of maize seedlings was observed during dark-to-light transitions. Intriguingly, 18.56-36.02 % of expressed genes and 61.13-73.02 % of accumulated metabolites were discernibly regulated by different types of light exposure. Co-expression network analysis revealed unique gene regulation patterns in maize seedlings subjected to different light conditions. In darkness, differentially expressed genes were predominantly associated with phenylpropanoid biosynthesis, DNA replication, and DNA repair processes. Far-red light was significantly associated with the circadian rhythm through ZmCCA1 and ZmLHY1 gene expression. Notably, red and blue light activated photosynthesis and glucose metabolism; ZmPIF5.1 emerged as a crucial regulator, upregulating the expression of light-harvesting complex subunits of the photosystem (ZmLHCA1 and ZmLHCB3), chloroplast lipoprotein (ZmCHL), and ribulose-1,5bisphosphate carboxylases (ZmRbcS1 and ZmRbcS2; i.e., carbon fixation enzymes), thereby facilitating chloroplast development and photosynthesis. This study elucidated the regulatory effects of different light treatments on maize seedling de-etiolation, providing greater understanding of maize growth and flowering in response to various light conditions.