Study Of After-ripening Mechanism On Seed Dormancy Release And QTL Analysis Of Seed Dormancy In Rice

Seed dormancy provides a strategy to survive adverse natural conditions in plants,while deep dormancy leads to inhibiting germination thereafter affecting crop production.Rice(Oryza sativa L.)is one of the most important food crop in the world.To understand the mechanism of seed dormancy release,and to explore dormancy gene are important for understanding the regulation of seed dormancy and germination in rice.It is valuable to prevent pre-harvest sprouting and to improve seed quality in future rice breeding programs.Therefore,the analysis of mechanism of after-ripening on seed dormancy release and QTL(quantitative trait loci)mapping for seed dormancy were conducted in this study.The main results as follows:1.After-ripening is a common method for dormancy release in rice.In this study,the variety Jiucaiqing(Oryza sativa L.subsp.japonica)was used to determine the dormancy release by different after-ripenings(1,2 and 3 months).The germination speed,germination percentage and seedling emergence were increased with after-ripening;a greater than 95%and 85%germination percentage and seedling emergence were observed after one month of after-ripening within 10 days of imbibition,respectively,while less than 45%and 20%germination percentage and seedling emergence in the freshly harvested seeds.Dormancy release by after-ripening is mainly correlated with the rapid decline of ABA content and the increases of GA and IAA content during imbibition.Subsequently,the GAs/ABA and IAA/ABA ratios were increased and GAs/IAA ratio was decreaed in after-ripened seeds thereby altering the a-amylase activities during seed germination.The peak of ?-amylase activities occurred at the earlier germination stage in after-ripened seeds than the freshly harvested seeds.The expressions of ABA,GA and IAA metabolism genes and dormancy related genes were regulated by after-ripening upon imbibition.By comparison,three months of after-ripening could be considered as a suitable treatment period for rice dormancy release.The increased expressions of OsCYP707A5,OsGA2ox1,OsGA2ox2,OsGA2ox3,OsILR1,OsGH3-2,qLTG3-1 and OsVPl while decreased expression of Sdr4 were obviously observed in imbibed seeds after 3 months of after-ripening.The dormancy release by after-ripening might be involved in the weakening of tissues covering embryo though qLTG3-1 and in the decreased ABA signaling and sensitivity though Sdr4 and OsVP1.2.A recombinant inbred line(RILs)population,derived from Jiucaiqing(japonica)and IR26(indica),was used to detect QTLs for seed dormancy.Three QTLs(qSD4.1,qSD9.1 and qSD9.2)were detected on chromosomes 4 and 9,respectively,each QTL explained 28.3%,30.6%and 20.6%of total phenotype variation.The chromosome segment substitution lines(CSSLs)popution,origined from the cross of Jiucaiqing(donor)and IR26(receptor),was used to identify and verify the QTLs for seed dormany among two years.Based on the phenotype of CSSLs,two lines CSSL36 and CSSL38 with the highest germinaiton percentage were selected.The germination percentage of CSSL36 and CSSL38 was significant higher than IR26(receptor),which indicating they had weak dormancy and the chromosome fragment from Jiucaiqing could reduce seed dormancy level.By the analysis of genotypes in CSSL36 and CSSL38,three QTLs(qSD3.1,qSD8.1 and qSD9.2)were detected on chromosomes 3,8 and 9.Of them,QTL qSD9.2 was simultaneously detected in both RILs and CSSLs polulations,suggesting it is a stably expressed major QTL for seed dormancy and the positive allele came from IR26.By comparing the chromosomal positions of these QTLs with those previously identified,there were no QTLs reported close to qSD8.1,qSD9.1 and qSD9.2,indicating these QTLs might be novel.These results might be applicable for the fine mapping and cloning of dormancy gene,and for the improvement of pre-harvest sprouting tolerance in rice.