Diversified mechanisms for regulating flowering time in a short-day plant rice

Abstract

Flowering in rice is influenced by not only endogenous factors that comprise an autonomous pathway, but also environmental effects, such as photoperiod, water availability, and temperature just before floral initiation. Recent molecular genetics studies have elucidated the functional roles of genes involved in the photoperiod pathway, e.g., photoreceptors, circadian clock components, and short-day (SD) promotion factors. Although these molecular players are well conserved between rice and Arabidopsis, their actual genetic functions are distinct. This is exemplified by Hdl (a CO counterpart) and phytochromes, in particular, rice PHYA. Hdl has a dual role in regulating flowering time and the expression of Hd3a (an FT counterpart) repression under long-day (LD) conditions while promotion under SDs. Models have been proposed to explain these photoperiod-dependent antagonistic activities. Some regulatory factors are present in only one of the model systems, e.g., FLC in Arabidopsis or Ehd1 in rice. Furthermore, epistatic relationships vary among such flowering regulators as Hd3a (FT), OsMADS50 (SOC1), and OsMADS14 (AP1). further experiments to probe these differences will be essential to enlarging our understanding of the diversified flowering regulation mechanisms in rice.