Hd1, a major photoperiod sensitivity quantitative trait locus in rice, is closely related to the arabidopsis flowering time gene CONSTANS

A major quantitative trait locus (QTL) controlling response to photoperiod, Hdl, was identified by means of a map-based cloning strategy. High-resolut ion mapping using 1505 segregants enabled us to define a genomic region of similar to 12 kb as a candidate for Hdl. Further analysis revealed that the Hdl QTL corresponds to a gene that is a homolog of CONSTANS in Arabidopsis . Sequencing analysis revealed a 43-bp deletion in the first exon of the ph otoperiod sensitivity 1 (se1) mutant HS66 and a 433-bp insertion in the int ron in mutant HS110. Se1 is allelic to the Hdl QTL, as determined by analys is of two se1 mutants, HS66 and HS110. Genetic complementation analysis pro ved the function of the candidate gene. The amount of Hdl mRNA was not grea tly affected by a change in length of the photoperiod. We suggest that Hdl functions in the promotion of heading under short-day conditions and in inh ibition under long-day conditions.