Transcriptome And Physiological Changes Of Dormancy Process In Bud Of Pyrus Pyrifolia Cultivars With Different Chilling Requirements

To investigate the physiological and molecular regulatory mechanisms behind the difference in chilling requirement of sand sand pears（Pyrus.pyrifolia）buds during the dormancy process and a better method to break dormancy,the bud tissues of sand pear varieties’Cuiguan’,’Cuiyu’,and’Wonhwang’with different cold requirements were selected for this study.In this study,the bud tissues were as the test materials to determine the chilling requirement through dormancy under natural conditions and the related physiological indexes in the process of natural dormancy of buds.The transcriptome sequencing and significant differential expression gene screening were performed on the bud tissues before and after dormancy and before and after cold storage;pear branches were treated with different chemicals at different dormancy stages.The main results are as follows.1.The chilling requirement of the test bud samples from the sampling site in Lishui in autumn and winter of 2020-2021 was,in descending order,’Cuiguan’vegetative buds（620 CU）,’Wonhwang’reproductive buds（556 CU）,’Cuiguan’reproductive buds（488 CU）and’Cuiyu’reproductive buds（191.5/396.8 CU）.Soluble protein,POD,GA₃,and IAA decreased with the deepening of dormancy and increased with the release of dormancy;proline showed an overall increasing trend after entering endodormancy;H₂O₂ and ABA contents increased in the early stage of dormancy and decreased with the release of dormancy.During dormancy,H₂O₂ content was highly significantly negatively correlated with the sprouting rate of all four shoot samples.The higher chilling requirement of sand pear may be related to the higher ABA/IAA,H₂O₂,and ABA/GA₃ and lower POD,IAA,and GA₃.‘Cuiguan’reproductive buds had higher ABA,POD,ABA/IAA,and soluble protein compared with vegetative buds.2.Some significantly differentially expressed genes were analyzed and screened by bioinformatics methods,based on FPKM values.Eight samples were compared two-by-two,and the number of up-regulated DEGs ranged from 487 to 1189,and the number of down-regulated DEGs ranged from491 to 1455,of which:LEA14 was significantly highly expressed in both reproductive buds and vegetative buds after entering dormancy and cold storage;six ARPs was up-regulated in’Cuiguan’reproductive buds after entering dormancy,while only Pb ARP01 was up-regulated in’Wonhwang’,and Pb ARP01/03/08 was up-regulated in’Cuiguan’after cold storage.Among the five DAM genes,Pp MADS28/71 were significantly highly expressed both after entering endodormancy and after cold storage.The expression of Ppy MADS28/71 and LEA14-a was higher in’Wonhwang’,which had a higher chilling requirement.3.The effect of artificial dormancy breaking was related to the treatment time and the concentration of the agent.’Cuiguan’isolated branches were treated with different concentrations of Calciun cyanamide,Hydrogen cyanamide,GA₃,and 5-aza C for chilling requirement has met 94.19%,and GA₃ treatment was the most effective.The live branches of’Wonhwang’’Cuiyu’were treated with five and eight times of Calciun cyanamide on different dates,and the treatment on January 22（when the cold requirement of’Wonhwang’had been met 96.31%and that of’Cuiyu’had exceeded 17.62%）.The treatment effect was better,and the suitable Calciun cyanamide concentrations for’Wonhwang’and’Cuiyu’were eight and five times of liquid Calciun cyanamide,respectively.Compared to the clear water control,the sprouting rate of’Wonhwang’branches was significantly increased by the eight times lime-nitrogen treatment on January 22.