Comparison Analysis Of Cold Tolerance And Key Differential Genes Function Of Prunus Mume

Mei（Prunus mume）is a traditional flower with high ornamental value in China.The improvement of cold resistance is the reproduction goals to expanding its cultivation area from South to North.Breeders crossed mei and apricot to produce apricot mei varieties that can safely overwinter in the North of china.However,the molecular mechanism of the stronger cold resistance of apricot mei is still unclear.In order to fully explain why apricot mei is more tolerant to cold than true mume.In this study,we used apricot mei’Dan Fenghou’and true mume’Beijing Yudie’,and their offspring’Xiang Ruibai’as the subjects.To systematically evaluate their tolerance ability and freezing pattern under low temperature stress.Transcriptomics,morphology and plant physiology were used to investigated the biological molecular mechanism of difference cold tolerance ability in various varieties.The main results were as follows.（1）There were significant differences in the cold resistance of the different varieties of mei.The cold resistance ability of’Xiang Ruibai’is between the parents.The LT50（semi-lethal temperature）of its annual branches of adult trees was-27.93°C,which higher than true mume’Beijing Yudie’LT₅₀₌-18.73℃but lower than apricot mei’Danfeng Hou’LT₅₀₌-44.92℃.The cold exercise ability of’Xiang Ruibai’was significantly higher than the two parents,which was enhanced by the accumulation of antioxidant activity.Antioxidant enzyme genes PmPOD4,PmPOD44,PmCZSOD2 and PmFLA3 expression levels were significantly increased in’Xiang Ruibai’.Indicating that’Xiangruibai’might enhance its cold resistance by enhancing antioxidant enzyme activities.（2）There were significant differences in the freezing point temperature of water in stems and buds of different varieties of mei under low temperature treatments.The freezing point temperature of the three varieties was counted using infrared technology and tree moisture detection.The freezing point temperatures of annual stems of apricot mei’Xiang Ruibai’and’Danfeng Hou’ranged from-4℃to-6℃in adult trees,which lower than true mume’Beijing Yudie’（between-3℃and-4℃）.The freezing point temperatures of annual grafted seedlings were consistent with the trend for adult trees.Probably because the stems of apricot mei avoid repeated freezing and thawing by lowering the freezing point temperature.The bud freezing point temperature of’Beijing Yudie’ranged from-7℃to-8℃,significantly lower than the two apricot mei varieties（between-6°C and-7°C）.The reason for the difference phenomenon may be that the mechanism of water subcooling in the bud of true mume is different from apricot mei.（3）A large number of transcription factors and protein modification genes expressed differentially in three varieties response to low temperature.The expression of PmWRKY18 and 55,PmNAC17 and 42,Pmb HLH78,PmCBFs and PmICEs increased significantly.Meanwhile,PmCBF3,4,8 and PmICE4 higher in’Beijing Yudie’and’Xiang Ruibai’than in’Danfeng Hou’.The protein kinase PmOST1,PmMPKs,E3ubiquitin ligase PmPUB1,15,23,and abscisic acid ABA synthesis PmXAN expression increased after 8 h of cold stress at 4°C and then returned to the initial expression level.They may have important roles in the process of low-temperature signal perception and transduction.（4）Genes encoding stress-related functional proteins were expressed cumulatively in the low-temperature exercise phase of the three species.Based on the functional enrichment results,these genes were mainly involved in the pathways of dehydrin synthesis,sugar transport or catabolism,and ubiquitination.Ubiquitin genes（PmPUB3,5,7,12）,dehydrin genes（PmLEAs）and sugar metabolism-related genes（PmGGPase1,PmGol S1,PmβA3,PmFBA1,PmSS3）were synthesized in large quantities at this stage and played important roles in removing misfolded proteins and maintaining normal cellular functions.（5）Numerous cell reconstruction-related genes were expressed at elevated levels during the post-freezing recovery phase in three species.The ubiquitin genes PmPUBs were involved in DNA repair and cell cycle regulation.High expression of PmCYP707A inhibited ABA synthesis and helped mei to enter a normal developmental state.At this time,the expression of transcription factors PmWRKYs,PmNACs and Pmb HLHs were elevated,they may be involved in the molecular regulation of cell reconstruction and tissue growth in mei.（6）The ion leakage rate index was strongly and positively correlated with the salmon module of WGCNA.Most of this module are genes acting on the cell membrane,which are involved in the regulation of cell membrane low temperature signal response and translocation.Combined with differential gene analysis,PmWRKY16,18 and 55 transcription factors were screened as candidate genes involved in the low temperature response of mei.（7）The involvement of transcription factors and ubiquitin genes in the mei adversity response was tentatively confirmed.The full-length c DNAs of six PmPUB genes and two PmNAC genes were obtained by cloning,and PmWRKY18 was cloned by research group.The overexpressingtransgenic tobacco for PmPUB1,PmPUB3 and PmWRKY18 genes were finally obtained.Observations on their growth and development phenotypes,phenotypes and physiology after low-temperature stress.The cold resistance of transgenic tobacco was significantly higher than control,which demonstrated that the three genes play a key role in the regulatory network related to low temperature stress.In conclusion,this is the first to examine the icing pattern of mei under low-temperature stress using infrared and tree moisture monitoring.Meanwhile,we analyzed the differences in cold resistance of different varieties of mei at the transcriptional level.Aiming to pave the way for more in-depth cold resistance studies and using molecular breeding to obtainednew varieties that have both the unique flower fragrance and color of mei and strong cold resistance.