Flower Development and Photoperiodic Control of Flowering in Rice

Floral transition,which is referred to as a plant＇s transition from vegetative stage to reproductive stage,is considered to be a critical developmental switch in higher plants,for a timely flowering is a major factor of reproductive success.Endogenous and environmental cues,such as photoperiod,light quality,plant hormones concentrations and temperature,provide information to the plants whether the environment is favorable for flowering.These cues promote,or prevent,flowering through a complex genetic network,mediated by a careful orchestration of temporal and spatial gene expression.One of such cues is photoperiod.Rice（Oryza sativa L.） serves as a powerful model species for the understanding of flowering in higher plants,including flower development and photoperiodic control of flowering.In this review,we overviewed and discussed the flower development and its model.We also overviewed the photoperiodic pathways in rice flowering control,and summarized the pathways at molecular level.

Nonfunctional alleles of long-day suppressor genes independently regulate flowering time

Due to the remarkable adaptability to various environments, rice varieties with diverse flowering times have abeen domesticated or improved from Oryza rufipogon.Detailed knowledge of the genetic factors controlling flowering time will facilitate understanding the adaptation mechanism in cultivated rice and enable breeders to design appropriate genotypes for distinct preferences. In this study,four genes（Hd1, DTH8, Ghd7 and OsPRR37） in a rice long-day suppression pathway were collected and sequenced in 154, 74,69 and 62 varieties of cultivated rice（Oryza sativa）respectively. Under long-day conditions, varieties with nonfunctional alleles flowered significantly earlier than those with functional alleles. However, the four genes have different genetic effects in the regulation of flowering time： Hd1 and Os PRR37 are major genes that generally regulate rice flowering time for all varieties, while DTH8 and Ghd7 only regulate regional rice varieties. Geographic analysis and network studies suggested that the nonfunctional alleles of these suppression loci with regional adaptability were derived recently and independently. Alleles with regional adaptability should be taken into consideration for genetic improvement. The rich genetic variations in these four genes,which adapt rice to different environments, provide the flexibility needed for breeding rice varieties with diverse flowering times.