on Chromosome 10 of Maize Delays Flowering of .

Maize () is a major cereal crop that originated at low latitudes, and thus photoperiod sensitivity is an important barrier to the use of tropical/subtropical germplasm in temperate regions. However, studies of the mechanisms underlying circadian regulation in maize are at an early stage. In this study we cloned on chromosome 10 of maize by map-based cloning. The gene is homologous to the Myb transcription factor genes / in ; the deduced Myb domain of ZmCCA1a showed high similarity with that of AtCCA1/AtLHY and ZmCCA1b. Transiently or constitutively expressed ZmCCA1a-YFPs were localized to nuclei of mesophyll protoplasts, agroinfiltrated tobacco leaves, and leaf and root cells of transgenic seedlings of . Unlike AtCCA1/AtLHY, ZmCCA1a did not form homodimers nor interact with ZmCCA1b. Transcripts of showed circadian rhythm with peak expression around sunrise in maize inbred lines CML288 (photoperiod sensitive) and Huangzao 4 (HZ4; photoperiod insensitive). Under short days, transcription of in CML288 and HZ4 was repressed compared with that under long days, whereas the effect of photoperiod on expression was moderate in HZ4. In overexpressing () lines, the circadian rhythm was disrupted under constant light and flowering was delayed under long days, but the hypocotyl length was not affected. In addition, expression of endogenous and the downstream genes , , and was repressed in seedlings. The present results suggest that the function of is similar, at least in part, to that of and , implying that is likely to be an important component of the circadian clock pathway in maize.