A major QTL and a candidate gene for heading date in an early maturing rice mutant induced by gamma ray irradiation

Abstract

Flowering time is an important trait associated with crop yield and quality. In a previous report, genome variation of significant DNA polymorphism was observed in the early maturing type rice mutant (EMT1) compared to that of wild type (WT). To identify quantitative trait loci (QTL) for flowering time, we constructed a linkage map of 36 InDel- and 6 SNP-markers with F₂ plants derived from the cross "WT × EMT1". One potential major QTL region was detected on chromosome 6. One gene of the QTL region, Heading date 1 (Hd1), exhibited relatively high nonsynonymous substitutions in the QTL region. To evaluate reliable allele segregation related to expected Mendelian ratio, M6-3 marker developed in the Hd1 gene exhibited clear monogenic segregation (1:2:1) in heterozygous F₃ plants. Both GI and Hd1 were highly induced at 56 days after sowing (DAS) in EMT1 and at 70 DAS in WT. The expression of Hd3a was significantly induced at 63 DAS, when Hd1 transcripts were slightly decreased compared with those at 56 DAS, while Hd1 was induced up to 84 DAS. These findings suggested that in EMT1, Hd1 could not suppress Hd3a under LD conditions, while OsMADS50 and LFY, which are involved in temperature responsive pathways, were significantly induced at 56 DAS, 14 days earlier than in WT.

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