AUTHOR=Shi Yong , Zhao Xiyong , Guo Sha , Dong Shifeng , Wen Yanpeng , Han Zanping , Jin Weihuan , Chen Yanhui 

TITLE=ZmCCA1a on Chromosome 10 of Maize Delays Flowering of Arabidopsis thaliana

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 11 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00078

DOI=10.3389/fpls.2020.00078

ISSN=1664-462X

ABSTRACT=Maize (Zea mays) is a major cereal that originated from low latitude zones, thus photoperiod sensitivity is one of the most important barriers for the use of tropical/subtropical germplasm in temperate regions.  However, studies into the mechanisms underlying circadian regulation in maize are just at the beginning.  We cloned ZmCCA1 on chromosome 10, which is a homolog of AtCCA1/AtLHY, by map-based cloning.  The Myb domain of the deduced amino acid sequence of ZmCCA1 shared high similarity with the Myb domain sequences of AtCCA1/AtLHY and ZmLHY (another homolog of AtCCA1/AtLHY mapped on chromosome 4 in maize); however, the C-terminal sequences were highly variable.  Transiently or constitutively expressed ZmCCA1-YFP localized to the nuclei of several plant cell systems.  Unlike AtCCA1 and AtLHY, ZmCCA1 did not form a homodimer or interact with ZmLHY.  Transcripts of ZmCCA1 showed circadian rhythm and peak expression around sunrise in maize inbred lines CML288 (photoperiod sensitive) and HZ4 (photoperiod insensitive).  Under short-day conditions the expression of ZmCCA1 in CML288 and HZ4 was repressed compared with under long-day conditions, but the effect on its expression in HZ4 was mild.  Overexpression of ZmCCA1 in Arabidopsis thaliana delayed flowering under the long-day condition, but the length of hypocotyl was not affected under short-day and constant dark conditions.  In addition, expression of endogenous AtCCA1/AtLHY and the downstream genes AtGI, AtCO, and AtFt was repressed in ZmCCA1-overexpressing seedlings.  Our results suggest that the function of ZmCCA1 is similar, at least in part, to the function of AtCCA1/AtLHY and ZmLHY, implying that ZmCCA1 may be a major component of the circadian clock pathway in maize.