Xing-You Gu, Jinfeng Zhang, Heng Ye, Lihua Zhang and Jiuhuan Feng

G3 (Genes, Gwenomes, Genetics) February 1, 2015 vol. 5 no. 2 183-193

Abstract

Seed dormancy is imposed by one or more of the embryo, endosperm, and maternal tissues that belong to two generations and represent two ploidy levels. Many quantitative trait loci (QTL) have been identified for seed dormancy as measured by gross effects on reduced germination rate or delayed germination in crop or model plants. This research developed an endosperm genotype−based genetic approach to determine specific tissues through which a mapped QTL regulates germination using rice as a model. This approach involves testing germination velocity for partially after-ripened seeds harvested from single plants heterozygous for a tested QTL and genotyping endosperms from individual germinated and nongerminated seeds with a codominant DNA marker located on the QTL peak region. Information collected about the QTL includes genotypic frequencies in germinated and/or nongerminated subpopulations; allelic frequency distributions during a germination period; endosperm or embryo genotypic differences in germination velocity; and genotypic frequencies for gametes involved in the double fertilization to form the sampled seeds. Using this approach, the seed dormancy loci SD₁₂, SD_1-2, and SD_7-1 were determined to regulate germination through the embryo, endosperm, and maternal tissues, respectively; SD₁₂ and SD_1-2 acted additively on germination velocity in the offspring tissues; and SD₁₂ also was associated with the preferential fertilization of male gametes in rice. This new genetic approach can be used to characterize mapped genes/QTL for tissue-specific functions in endospermic seeds and for marker-assisted selection of QTL alleles before or immediately after germination in crop breeding.

Figure 1 Electrophoresis patterns of endosperm genotypes for codominant markers. (A) Comparison between endosperm and embryo genotypes of same seeds. (B) Segregation patterns for four endosperm genotypes of F₂ seeds. RID12, RM315, and SD12m13 were selected to mark the seed dormancy loci SD_7-1, SD_1-2, and SD₁₂, respectively. Gel images show electrophoresis patterns for individual F₂ seeds from germinated subpopulations. The genotypes are indicated by combinations of the dormancy-enhancing (D) and/or -reducing (d) alleles, or by the copy number of the D allele (0−3) at a locus.