Genetic Action Of Hd1 When Its Functional Allele Loses Photoperiod Sensibility

Heading date( HD) is the most vital factor determining the regional and seasonal adaptation of rice, which is closely associated with yield potential. Therefore, exploration the molecular mechanism for flowering and investigation the genetic relationship between heading date and yield traits are crucial important in high-yield breeding of rice. Hd1 is a key regulator for rice HD and photoperiod sensitivity(PS), which contributes to diversity of flowering time in cultivated rice. The PS allele of Hd1 loses its photoperiod sensibility, which plays an improtant role in adpation of long-day condition for early-season rice variety. Zhenshan97(ZS97) and Milyang46(MY46) are early season variety with non- PS and middle season variety with weak-PS, respectively. In this study, several segregation populations constucted from ZS97/MY46 were used for charecterization of QTL for HD. Genetic effects of PS allele of Hd1 when it loses its photoperiod sensibility allele on HD, plant height and yield traits were elucidated. And effects of Hd2 in the presence of photoperiod-insensitive functional allele of Hd1 were also analyzed. The main results were summarized as follow:A near isogenic line-F2(NIL-F2) population was constructed from a residual heterozygote of ZS97/MY46. In this population with the background of the parental mixture, the PS allele der ived from ZS97 promoted and delayed flowering by 6.99 and 6.98 d in the natural short-day and long-day conditions, respectively. Eight backcross populations were developed using ZS97 as the recurrent parent and MY46 as the donor, including two BC2F6 populations, three BC2F7 populations and three sets of NIL. In these backcross populations with the background of ZS97, no response to the photoperiod was observed, whereas ZS97 allele functioned in promoting flowering, decreasing plant height and grain productivity. The additive effects estimated in two NIL sets were 6.14 and 6.14 d for heading date, 4.46 and 5.55 cm for plant height, 10.82 and 11.54 for the number of spikelets per panicle, 6.82 and 8.00 for the number of grains per panicle, and 2.16 and 2.23 g for grain yield per plant.Rice populations in which the photoperiod-sensitive allele at Hd1 has become insensitive to photoperiod but remained to affect HD were constructed, including seven NIL-F2 populations and one set of NIL. The NIL-F2 populations were segreated in the region on the distal end of the long arm of chromosome 7, which covered a QTL for HD detected previously. The NIL contained the four homozygous genotypic combinations of the target QTL and Hd1. Using the seven populations, the QTL was delimitated to a 96.3-kb region on the distal end of the long arm of chromosome 7. Sequence comparison revealed that this QTL is identical to Hd2. In all the NIL-F2 populations and the NIL set, the functional Hd2 allele from MY46 was insensitive to photoperiod and it delayed f lowering under both natural short and long day condition. The digenetic interaction between non-photoperiod-sensitive components of Hd1 and Hd2 were analyzed using the NIL set by two-way ANOVA. They were found to largely act additively in regulating HD and yield traits, and showed duplicate action in increasing plant height.