ZmMADS69 functions as a flowering activator through the ZmRap2.7-ZCN8 regulatory module and contributes to maize flowering time adaptation.

Flowering time is a major determinant of the local adaptation of plants. Although numerous loci affecting flowering time have been mapped in maize, their underlying molecular mechanisms and roles in adaptation remain largely unknown. Here, we report the identification and characterization of MADS-box transcription factor ZmMADS69 that functions as a flowering activator through the ZmRap2.7-ZCN8 regulatory module and contributes to adaptation. We show that ZmMADS69 underlies a quantitative trait locus controlling the difference in flowering time between maize and its wild ancestor, teosinte. Maize ZmMADS69 allele is expressed at a higher level at floral transition and confers earlier flowering than the teosinte allele under long days and short days. Overexpression of ZmMADS69 causes early flowering, while a transposon insertion mutant of ZmMADS69 exhibits delayed flowering. ZmMADS69 shows pleiotropic effects for multiple traits of agronomic importance. ZmMADS69 functions upstream of the flowering repressor ZmRap2.7 to downregulate its expression, thereby relieving the repression of the florigen gene ZCN8 and causing early flowering. Population genetic analyses showed that ZmMADS69 was a target of selection and may have played an important role as maize spread from the tropics to temperate zones. Our findings provide important insights into the regulation and adaptation of flowering time.

The circadian clock-associated gene gigantea1 affects maize developmental transitions.

The circadian clock is an internal timing mechanism that allows plants to make developmental decisions in accordance with environmental conditions. In model plants, circadian clock-associated gigantea (gi) genes are directly involved in control of growth and developmental transitions. The maize gigantea1 (gi1) gene is the more highly expressed of the two gi homeologs, and its function is uncharacterized. To understand the role of gi1 in the regulatory networks of the maize circadian clock system, gi1 mutants were evaluated for changes in flowering time, phase change and growth control. When grown in long-day (LD) photoperiods, gi1 mutants flowered earlier than non-mutant plants, but this difference was not apparent in short-day (SD) photoperiods. Therefore, gi1 participates in a pathway that suppresses flowering in LD photoperiods, but not in SD. Part of the underlying cause of early flowering was up-regulated expression of the FT-like floral activator gene zea mays centroradialis8 (zcn8) and the CONSTANS-like flowering regulatory gene constans of zea mays1 (conz1). gi1 mutants also underwent vegetative phase change earlier and grew taller than non-mutant plants. These findings indicate gi1 has a repressive function in multiple regulatory pathways that govern maize growth and development.