Sdr7, A Quantitative Trait Locus for Seed Dormancy in Rice, Encodes an Ortholog of the Arabidopsis Protein Delay of Germination 1

Preharvest sprouting resistance is an important agronomic trait of rice, since preharvest sprouting reduces grain quality. The level of seed dormancy is an important component of varietal variation in the resistance. To isolate a gene involved in seed dormancy and to understand the genetic control of dormancy, we attempted to delimit the candidate region of Seed dormancy 7 (Sdr7), a quantitative trait locus, in progeny of ‘Sasanishiki’ ´ ‘Habataki’. High-resolution mapping identified a 46-kb genomic region on chromosome 1 as a candidate. Sequence comparison of the candidate region of each parent identified a homolog of Arabidopsis Delay of Germination 1 (DOG1) as a probable candidate. Transgenic plants with a 4-kb Habataki genomic fragment of this DOG1-like gene region showed sprouting resistance, confirming that this region encodes Sdr7. Overexpression of Sdr7 cDNA under the control of the CaMV35S promoter inhibited germination. The transcription of Sdr7 mRNA was induced in imbibed dormant seeds after 9 h, but not in non-dormant seeds. These results suggest that transcriptional regulation of Sdr7 plays an important role in seed dormancy. We found several DOG1-like genes in the rice genome. To investigate their function, we isolated 2 mutant alleles, OsDOG1-L2 and OsDOG1-L3, from japonica rice by TILLING (targeting induced local lesions in genomes). Germination experiments revealed that plants with each mutant allele were viviparous. These observations indicate the conservation of at least part of the genetic control of seed dormancy between rice and Arabidopsis.