Determination Of Abscission Related Enzyme Activities And Transcriptome Analysis Of Malus Spp.

Ornamental crabapple is an excellent ornamental tree species of Rosaceae,which integrates ornamental flowers,leaves,and fruits.The length of the fruit setting period has a great influence on the ornamental value of its fruit.It is of great significance to explore the internal causes of the abscission of Malus spp.fruit.In this experiment,Malus spp.‘Radiant’,Malus spp.‘Flame’,Malus spp.‘Donald Wyman’,Malus spp.‘Red Jewel’,Malus spp.‘Sugar Tyme’,those five ornamental crabapple varieties were used as test materials.The position of the fruit abscission layer was determined by wood slice observation,and the changes of pectinase,polygalacturonase,cellulase,andβ-glucosidase in the abscission layer were determined.The relationship between related enzyme activities in the abscission layer of ornamental crabapple and fruit abscission was explored.The relative expression levels of the above cell wall degrading enzyme synthesis genes McPEM,McCEL,McBG,and McGC in different populations were determined,and other related genes and transcription factors involved in regulating fruit abscission of ornamental crabapple were further screened by transcriptome data.To reveal the mechanism of ornamental crabapple fruit abscission,and provide a more theoretical basis for the breeding of ornamental crabapple varieties and further improve the ornamental value.The results of this study are as follows :(1)The microstructure observation of the fruit stalk abscission layer showed that the abscission layer was formed at the base of fruit stalk in varieties Malus spp.‘Radiant’ and Malus spp.‘Flame’ before fruit abscission,and the cell volume of the abscission layer was small and the cytoplasm was dense.At the same time,no abscission layer was formed at the base of fruit stalk in varieties,Two special structures including inner phloem and outer phloem vascular tissues were found in the transverse section structures of short branches of Malus spp.varieties Malus spp.‘Radiant’,Malus spp.‘Flame’,Malus spp.‘Donald Wyman’,Malus spp.‘Red Jewel’ and Malus spp.‘Sugar Tyme’.(2)The results of cell wall degrading enzyme activity showed that there were significant differences in the activities of four enzymes in different varieties at the same period.Pectin esterase activity,polygalacturonase activity,and β-glucosidase activity of Malus spp.‘Radiant’ and Malus spp.‘Flame’ increased during fruit abscission except cellulase activity decreased slightly,and the enzyme activity was higher than that of Malus spp.‘Donald Wyman’,Malus spp.‘Red Jewel’ and Malus spp.‘Sugar Tyme’,which fell relatively late.The results showed that the abscission of Begonia fruit was related to cellulase activity,and the increase of pectinase activity,polygalacturonase activity,and β-glucosidase activity in the abscission layer of fruit stalk promoted the abscission of fruit.(3)Transcriptome results showed that a total of 802 differentially expressed genes were screened by comparing the early and late abscission groups of ornamental crabapple fruits.These genes were significantly enriched in phenylpropanoid biosynthesis,linoleic acid metabolism,cyanidin metabolism,and other metabolic pathways.Through the analysis of differential genes,a total of twenty-nine genes were screened was involved in the process of ornamental crabapple fruit abscission,and the specific function needs to be further verified.The relative expression levels of McPEM,McCEL,McBG,and McGC in the fruit stalk abscission region were measured and analyzed by RT-qPCR.It indicates that McPEM,McCEL,McBG and McGC may promote fruit abscission.