Molecular dissection of a dormancy QTL region near the chromosome 7 (5H) L telomere in barley

Abstract

Moderate seed dormancy is desirable in barley (Hordeum vulgare L.). It is difficult for breeders to manipulate seed dormancy in practical breeding programs because of complex inheritance and large environmental effects. Quantitative trait locus (QTL) mapping opens a way for breeders to manipulate quantitative trait genes. A seed dormancy QTL, SD2, was mapped previously in an 8-cM interval near the chromosome 7 (5H) L telomere from a cross of 'Steptoe' (dormant)/'Morex' (non-dormant) by the North American Barley Genome Project using an interval mapping method and a relatively low-resolution genetic map. SD2 has a moderate dormancy effect, which makes it a promising candidate gene for moderate seed dormancy in barley cultivar development. The fine mapping of SD2 is required for efficient manipulation of SD2 in breeding and would facilitate the study of dormancy in barley. Ten different Morex isolines were generated, including regenerated Morex, of which nine lines had duplicates. The isolines together with Steptoe and Morex were grown in growth room and field environments for 2 years (2000 and 2001). In the growth room, relatively low growing temperatures (25 degrees C day/15 degrees C night) were employed to promote seed dormancy development. Seed germination percentage, determined at different post-harvest after-ripening periods, was used to measure seed dormancy. Fine mapping using the substitution mapping method based on differences among isolines resolved the SD2 QTL into an 0.8-cM interval between molecular markers MWG851D and MWG851B near the chromosome 7 (5H) L telomere. Relatively low temperatures (< or =25 degrees C) during seed development promoted the expression of the SD2 dormancy QTL. The chromosome region above the MWG851D-MWG851B interval might play a role in reducing barley seed dormancy during after-ripening.

Isolation of three dormancy QTLs as Mendelian factors in rice

“…Several dormancy QTL regions have been isolated in introgression or near isogenic lines for Arabidopsis, barley, and rice (Han et al, 1999;Alonso-Blanco et al, 2003;Gao et al, 2003;Takeuchi et al, 2003). Fine mapping these regions suggests: (1) a dormancy QTL may consist of a gene cluster (Han et al, 1999); (2) some dormancy QTLs may lose their effect in a nondormant genetic background (Alonso-Blanco et al, 2003); (3) some QTLs are especially sensitive to the environment during seed development (Gao et al, 2003); and (4) an influence of flowering time on dormancy may be due to tight linkage between loci for both traits (Takeuchi et al, 2003).…”

“…Fine mapping these regions suggests: (1) a dormancy QTL may consist of a gene cluster (Han et al, 1999); (2) some dormancy QTLs may lose their effect in a nondormant genetic background (Alonso-Blanco et al, 2003); (3) some QTLs are especially sensitive to the environment during seed development (Gao et al, 2003); and (4) an influence of flowering time on dormancy may be due to tight linkage between loci for both traits (Takeuchi et al, 2003). Some of the introgression lines were used to estimate geneadditive effects for the QTL.…”

Genetic analysis of seed dormancy QTL in barley

“…A similar strategy was taken to develop substitution lines from crosses between selected Steptoe/Morex DH lines. By using these sets of lines, mapped the SD1 locus to a 4.4 cM marker interval, and Gao et al (2003) mapped the SD2 locus to a 0.8 cM marker interval. As illustrated by these two examples, specific populations are a key resource for developing high resolution maps for cloning QTL.…”

Phenotypic Selection for Dormancy Introduced a Set of Adaptive Haplotypes From Weedy Into Cultivated Rice

“…Both dormancy and PHS are complex traits controlled by many genes (Chang and Tagumpay 1973) or quantitative trait loci (QTL) such as in Arabidopsis (Alonso-Blanco et al 2003), barley (Oberthur et al 1995;Li et al 2003;Prada et al 2004;Zhang et al 2005), rice (Lin et al 1998;Cai and Morishima 2000;Dong et al 2003;Gu et al 2004), sorghum (Lijavetzky et al 2000), and wheat (Anderson et al 1993;Kato et al 2001;Mares and Mrva 2001;Groos et al 2002;Osa et al 2003;Kulwal et al 2004). Dormancy alleles at a few QTL have been introduced into the nondormant genetic background to validate their effects or to explore their potential in breeding programs (Han et al 1999;Gao et al 2003;Takeuchi et al 2003). Validated QTL may be cloned to characterize molecular mechanisms directly regulating germination and dormancy (Koornneef et al 2002).…”