Photoperiodic flowering without CO: promotion of Medicago flowering by PHYA and legume-specific E1

M Jaudal, L Zhang, G Thomson and J Putterill

University of Auckland, New Zealand

Day length (photoperiod) is crucial to the control of flowering time in many plants. In eudicots, the photoperiod pathway is best studied in Arabidopsis – where long day (LD) floral induction depends on interactions among the circadian clock, photoreceptors and flowering time genes such as CO. CO is activated by LD and directly triggers expression of the powerful floral activator FT. However, CO does not appear to function in the temperate-climate legumes pea and Medicago. On the other hand, the photoreceptor PHYA is an important regulator of photoperiodic flowering in Arabidopsis, pea and short-day soybean. Work in soybean has also uncovered legume-specific responses downstream of PHYA. For example, in non-inductive LD, soybean PHYA promotes expression of the legume-specific E1 gene that represses flowering. We are using the powerful genetic and genomic resources of Medicago to investigate how flowering time is regulated in this reference legume. We will present data indicating that MtPHYA and MtE1 both promote flowering in Medicago. PHYA appears to function as a major player in Medicago flowering time control in LD that positively regulates E1 and FT-like transcript accumulation and modulates expression of some clock genes.