Temporal Shift of Circadian-Mediated Gene Expression and Carbon Fixation Contributes to Biomass Heterosis in Maize Hybrids

we determine genome-wide binding profiles of a maize CCA1 homolog, ZmCCA1b, in maize inbreds and F1 hybrids at different times of the day. ZmCCA1b is characterized as a central clock regulator gene with evolutionarily conserved molecular and circadian functions and nonadditively expressed in F1 hybrid seedlings. ZmCCA1b binds to over 4,300 target genes in the maize genomes, of which annotation confirms energy metabolic pathways as the main output. We report that an altered temporal binding activity of ZmCCA1b in the hybrid seedlings, which increases expression of carbon fixation genes, increases carbon fixation rates and biomass, demonstrating a novel example of how circadian-regulatory networks directly contribute to growth vigor in maize hybrids. These results collectively offer new insights into clock-mediated regulation of growth vigor in hybrid plants and crops. Overall design: Profiling genome-wide binding events of ZmCCA1b in the maize inbreds and F1 hybrids at ZT3, ZT9 and ZT15 using chromatin immunoprecipitation followed by deep sequencing (ChIP-seq). 2 biological replicates for each sample were used. Input DNA sample corresponding to each ChIP sample was also sequenced in parallel. We have developed a native antibody for the protein (GRMZM2G014902; epitope: residues 11-77) for the ChIP-seq study.