FINE SCALE GENETIC AND PHYSICAL MAPPING OF HD6, A QUANTITATIVE TRAIT LOCUS INVOLVED IN PHOTOPERIOD SENSITIVITY IN RICE.

¹ Institute of the Society for Techno-innovation of Agriculture, Forestry and Fisheries, Tsukuba, Ibaraki 305-0854, Japan

² National Institute of Agrobiological Resources, Tsukuba, Ibaraki 305-8602, Japan

³ Bio-oriented Technology Research Advancement Institution, Omiya, Saitama 331-8537, Japan

Several quantitative trait loci controlling heading date in rice were identified by using a population derived from a cross between japonica variety Nipponbare and indica variety Kasalath. In backcross progeny derived from the same parents, Hd6 was mapped on the long arm of chromosome 3. At the Hd6 locus, the Kasalath allele is dominant and increases days-to-heading. A day length treatment test of a near-isogenic line revealed that Hd6 is a photoperiod-sensitivity gene. To determine the precise location of Hd6, we performed linkage analysis with about 1200 segregating plants using cleaved amplified polymorphic sequence (CAPS) and restriction fragment-length polymorphism (RFLP) markers. We also constructed a yeast artificial chromosome (YAC) contig around Hd6 and identified target YACs. We mapped new RFLP markers from the ends of the YACs or from expressed sequence tags (ESTs) mapped on the YACs for further linkage analysis and mapped Hd6 on these fine scale maps by progeny testing. We next screened a P1-derived artificial chromosome (PAC) library and made a PAC contig encompassing Hd6. A restriction map of these PAC clones indicated that the Hd6 locus was within an 80-kb genomic region. We are now using sequencing analysis of selected PAC clones and construction of a cosmid clone contig of the Hd6 region to identify the gene encoding Hd6.