Natural variation in rice flowering time
Accumulating evidence for the SD flowering pathway
allowed us to explore the molecular nature of flowering
time diversity in rice [16
]. Cultivated rice varieties show
substantial diversity in flowering time under SD conditions, and comprehensive analyses by combining gene
expression studies, sequence comparisons and transient
expression assays revealed that early flowering during SD
is well correlated with high expression of Hd3a. Moreover, this crucial variation in Hd3a expression is contributed mainly by the Hd3apromoter sequence, Hd1
functional polymorphisms, and Ehd1expression level
(Figure 1). These results share an important aspect in
the natural variation of florigen genes because recent
reports identified that the ArabidopsisFTpromoter also
has variations contributing to flowering time differences
[33], but there is a striking contrast with the situation in
Arabidopsis in which the major determinant of flowering
time diversity was found at vernalization related loci [34].
The allelic variation of another flowering time gene in
rice,Ghd7(forGrain number, plant height, and heading date
7), is also associated with the latitude of the cropping area