The Relationship Of ABA Metabolism And Regulation To Seed Germination Heterosis Between Hybrids And Its Parental Inbred Lines In Maize(Zea Mays L.)

Heterosis is a widespread biological phenomenon.Maize is the most important food crop in the world and has become one of the model crop for the heterosis utilization and research.In this thesis,we used the maize hybrid B73/Mo17 and its parental lines as materials and thorough studied the relationship between ABA and seed germination heterosis from different aspects:phenotype,hormone,gene expression and regulation and cell.The main results were summarized as follows:1.We found that the seed germination rate of hybrid B73/Mo17 was significantly faster than that of its parental lines.The T50 of parental inbred lines B73 and Mo 17 was greatly increased by exogenous ABA treatment compared with the hybrid B73/Mo17.These results suggested that hybrid B73/Mo17 is less sensitive to the exogenous application of ABA,which was consistent with the faster decrease of ABA content in the hybrid during seed germination,indicating that ABA inactivation plays an important role in seed germination heterosis.2.We investigated the expression patterns of ABA inactivation genes during seed germination and found that Only ZmABA8ox1a and ZmABA8ox1b were expressed at detectable levels.The expression level of ZmABA8oxlb rapidly increased and displayed an above high parent or high parent expression pattern at the early stage of seed germination.In Arabidopsis,the overexpression transgenic lines of ZmABA8ox1b showed lower ABA content in dry seeds and faster seed germination rate compared with the wild type.Therefore,we proposed that ZmABA8oxlb played a key role in seed germination heterosis.3.Cell expansion,not cell division,in the upper region of the embryo radicle in maize was the main reason of radicle emergence.Further studies confirmed that the cell expansion rate in hybrid was faster than in its parental lines and that the decrease in cell length in the parents after ABA treatment was significantly larger than in the hybrid,which was consistent with the result of ABA measurement.Moreover,oryzalin had no effect on seed germination rate.These results suggested that ABA influenced seed germination heterosis by regulating cell expansion.4.Global gene expression profiles in seed embryos of hybrid B73/Mo17 and its parents at 16 HAI was established and compared.2776 nonadditively expressed genes were divided into six expression patterns:high parent(466),low parent(661),above high parent(400),below low parent(278),partial dominance(671)and others(200).We also analyzed genome-wide gene expression profiles in seed embryos of the parental line B73 under exogenous ABA treatment at 16 HAI.The 3981 differentially expressed genes included 1775 ABA-induced genes and 2206 ABA-repressed genes.Further analysis of cell wall and DNA metabolism genes showed that 87.50%genes which was induced by ABA and belonged to nonadditively expression genes were displayed low parent or below low parent expression pattern,and that 89.13%genes which was repressed by ABA and belonged to nonadditively expression genes were displayed high parent or above high parent expression pattern.These results indicated that ABA might regulate seed germination heterosis through cell wall and DNA metabolism.5.Histone acetylation changed significantly during seed germination.H3K9ac and H3K14ac rapidly increased at 0-8 HAI and then declined after 8 h imbibition,and displayed above high parent and below low parent at 8 and 16 HAI,respectively.H4K5ac and H4K12ac rapidly decreased during seed germination and displayed above high parent at 16 HAI.