Photoperiodic regulation of flowering in perennial ryegrass involving a CONSTANS -like homolog.

Photoperiod and vernalization are the two key environmental factors of the floral induction of perennial ryegrass (Lolium perenne L.). Transition from vegetative to reproductive growth will only occur after an extended vernalization period, followed by an increase in day length and temperature. Here we report on the isolation and characterization of a L. perenne gene (LpCO ) that is homologous to CONSTANS , and which is tightly coupled to the floral inductive long day signal. Like other monocot CO-like proteins, the LpCO contains a zinc finger domain with a non-conserved B-Box2. Although the B-Box2 has been demonstrated to be essential for the function of the Arabidopsis CO (AtCO), LpCO is able to complement the Arabidopsis co-2 mutant, and ectopic expression in Arabidopsis wild type leads to early flowering. The LpCO transcript exhibits diurnal oscillations and is expressed at higher levels during long days.