Abstract
Heading date 3a (Hd3a) has been detected as a heading-date-related quantitative trait locus in a cross between rice cultivars. Kasalath allele of Hd3a confers earlier heading than the Nipponbare allele under short-day (SD) condition. We identified Hd3a gene by map-based cloning. Hd3a is an ortholog of FT, a flowering inducer in Arabidopsis. We showed that the accumulation of Hd3a mRNA induces floral transition in rice and Arabidopsis. Expression analysis revealed that the amount of Hd3a mRNA is up-regulated by Hd1, a homolog of CONSTANS (CO), under SD condition. Our results indicate that the function and regulatory relationship with Hd1 and CO, respectively, of Hd3a and FT genes are conserved between rice (an SD plant) and Arabidopsis (a long-day plant). We demonstrated that Hd3a and FT response to opposite photoperiods, although the diurnal oscillation pattern of Hd1 mRNA abundance was similar to that of CO.
