The Primary Characterization Of Molecular Mechanism On Shallow Dormancy Formation Of Giant Embryo Mutant Rice

Seed dormancy refers to a phenomenon that a dynamic seeds can not germinate in the appropriate environmental conditions.The depth of seed dormancy is closely related to whether it is easy to pre-havest sprout,Damage to seed dormancy often causes poor grain quality and results in significant reductions in yield,leading to significant economic losses.In contrast,deep dormancy can lead to equally unwanted nonuniform germination.Therefore,a suitable level of dormancy is critically important agronomic trait.Our understanding of seed dormancy depends mainly on studies especially in dicotyledonous model plant Arabidopisis.Although many studies on rice dormany and pre-harvest spouting have also been reported,researches on dormancy of giant embryo rice have,however,not been reported.“Shangshida No.5” is a new kind of giant embryo rice,which was obtained in the regeneration of “Chao 2-10” rice mature embryos.The embryo of “Shangshida No.5” is two-three times bigger than “Chao 2-10”rice.Giant embryo rice is popular with consumers because giant embryo rice seeds are rich in γ-amino butyric acid(GABA),Vitamin E and unsaturated fatty acid.However,in the field for agricultural production,“Shangshida No.5” exhibits higher pre-harvest spouting rate than “Chao 2-10”,which seriously reduces its yield and quality.Ready pre-harvest spouting of “Shangshida No.5” occurs at rice mature stage when high temperature and rain come.In this study,we investigated the possible mechanisms underlying the easy pre-harvest spouting of “Shangshida No.5”.Study on the Pre-harvest sprouting in giant embryo rice “Shangshida No.5”: In this study,we first tested the ABA sensitivity of “Shangshida No.5”.The results showed that the sensitivity of “Shangshida No.5” to ABA was more reduced than “Chao 2-10”,indicating that “Shangshida No.5” spouting is caused by shallow dormancy.This result was further confirmed by analyses of water content and ɑ-amylase activity,which showed that “Shangshida No.5” had significant higher water and amylase activity than those of “Chao2-10”.In addition,the result of real-time quantitative PCR showed that expression levels of three dormany related genes Os VP1、Os Sdr4、Os TRAB1 in “Chao 2-10” were higher than those in “Shangshida No.5” during different imbibition times,indicating a lower dormany potential of “Shangshida No.5” than “Chao 2-10”.Analysis of metabolomics differences of “Shangshida No.5” and “Chao 2-10” during different imbibition stages: In this study,we used metabolomics to explore the possible causes of shallow dormancy of giant embryo rice.The results showed that,as compared with “Chao 2-10”,content of sulfur compounds(dormancy promoting chemicals)such as methionine were significantly higher in “Shangshida No.5”,while flavonoids that inhibit germination were significantly lower in “Shangshida No.5” during different germination stages.In addition,clusting analysis results results showed that amino acids and carbohydrates were accumulated earlier in the endosperm of “Shangshida No.5” than in “Chao 2-10”.These analysis revealed,from a metabolomics level,that the shallow dormancy in “Shangshida No.5” than “Chao 2-10” possess solid biochemical basis as well.In the present study,the courses of pre-harvest sprouting in giant embryo rice seeds were explored for the first time by combining physiological studies with molecular and metabolomi approaches.This study will lay a solid foundation for the further exploration of the shallow dormany mechanism of “Shangshida No.5” giant embryo rice in the future,and it is expected to provide a mew way to improve the preharvest sprouting of giant embryo rice.