[en] Flowering time in plants is controlled by a number of environmental factors, among which photoperiod plays a key role. Maize ancestors are short-day (SD) plants, but breeding programs have selected genotypes whose flowering is largely autonomous and occurs after production of a constant number of leaves regardless of photoperiod. Only few flowering time genes have been identified in maize; one of them is INDETERMINATE1 (ID1), cloned from a late-flowering mutant and encoding a zinc finger transcription factor. By contrast, the genetical control of flowering by photoperiod is best understood in the long-day (LD) dicot Arabidopsis and the SD monocot rice. A key regulator is the CONSTANS gene that mediates between the circadian clock – the time-keeper of the plant – and the synthesis of flowering signals. Here we report the analysis of a CONSTANS homolog in maize, ZmCO, in SD and in LD, and in different parts of the plant. Expression of ZmCO was found to be rhythmic and to be much higher in young leaf primordia than in mature leaf blades. Striking coincidence was observed with expression of ID1.
