Physiological Effects And Transcriptome Analysis On Osmopriming Attenuated Thermal Dormancy Of Fraxinus Mandshurica Rupr.Seeds

Under the background of global climate change,seed secondary dormancy has been widely observed in production practice.At present,studies on secondary dormancy are mainly focused on inducing or releasing conditions,while the physiological changes and regulation of gene expression are not clear.It is known that mass fraction 500 g/L polyethylene glycol(PEG)at 10 ℃for 7 d can attenuate Fraxinus mandshurica seeds thermal dormancy,but the physiological changes or gene expression during this process are not clear.Therefore,non-dormant Fraxinus mandshurica seeds were used as materials,to determine the changes of endogenous hormone content,cell wall degrading enzyme and antioxidant enzyme activity of PEG primed seeds during germination after high temperature induction,and to conduct transcriptome sequencing(RNA-Seq)analysis of seeds before and after high temperature induction.Seeds without priming treatment were used as control.It is aimed to determine the gene expression of Fraxinus mandshurica seeds were affected by osmopriming to reduce thermal dormancy,enrich the regulation theory of secondary dormancy and lay foundation for molecular studies.The main results are as follows:(1)In the germination process,osmopriming seeds embryo ABA content gradually decreased,while embryo and endosperm GA content increased,embryo ETH content significantly increased.And seed endosperm cellulase and embryo pectinase activity significantly increased.By regulating the synthesis of related germinating hormones and weakening the endosperm inhibition effect of embryo elongation to attenuate thermal dormancy of seeds and promotes germination.POD activity of embryo and endosperm increased,it enhanced the scavenging ability of reactive oxygen species,inhibited the peroxidation of cell membrane,and maintained the stability of cell structure,resulting in MDA content of seed embryo and endosperm decreased significantly,but there was no significant difference between seeds germinated at appropriate temperature.(2)Osmopriming treatment have different gene expressed ways of seeds different parts in response to high temperature.Before high temperature induction,the DEGs in seed embryo and endosperm were mainly up-regulated expressed,after high temperature induction,the endosperm DEGs were mainly down-regulated,and which in embryo were mostly up-regulated expressed.And the number of differentially expressed genes(DEGs)in seeds endosperm was significantly more than that in embryo,indicating that the effect of priming treatment on the gene expression in seed endosperm was more significant.(3)In addition to the basal metabolism(TCA cycle,glycolysis/gluconogenesis and amino acid metabolism)that provide energy for germination,osmopriming seeds embryo and endosperm DEGs were mainly involved in phenylpropanoid biosynthesis,plant hormone signal transduction and glutathione metabolism.Without high temperature induction,the differential genes regulating the pathways of phenylpropanoid biosynthesis,glutathione metabolism and proline metabolism in endosperm were significantly up-regulated,and secondary metabolites such as lignin and cellulose were synthesized to resist environmental stress.At the same time,active antioxidants such as glutathione and proline were generated to maintain the balance of reactive oxygen metabolism and reduce the damage of cell structure.DEGs regulating ABA receptor(PYR/PYL)and ABA negative regulator(PP2C)together to prevent signaling downstream and inhibit endosperm ABA synthesis.The positive regulator of ethylene(SIMK kinase)was significantly up-regulated in seed embryos,promoting the synthesis of ETH and seed germination.After high temperature induction,DEGs related to stress responses such as secondary metabolism and stimulus response was down-regulated in endosperm,and the DEGs encoding GA negative regulatory factor(DELLA)and seed embryo PYR/PYL were downregulated significantly,which synergically regulated GA and ABA hormone levels to promote seed germination.In summary,Osmopriming treatment can enhance the seeds resistance to stress and activated reactive oxygen species scavenging system to reduce cell damage by up-regulating the pathways of phenylpropanoid biosynthesis,glutathione metabolism and MAPK signal transduction in endosperm.Meanwhile,seeds endosperm GA,ETH synthesis signals were upregulated,while embryo and endosperm ABA synthesis signals was down-regulated,to regulate the level of GA,ABA and other hormones,and synergically attenuated Fraxinus mandshurica seed thermal dormancy.