Identification Of PG Gene Family In Durian And Pectin Changes During Fruit Dehiscence

Durio Zibethinus Murr,known as the king of tropical fruits,is popular among consumers for its unique taste and rich nutritional value.Durian has been categorized as a climacteric fruit.The release of endogenous ethylene after harvest leads to the cracking of the softened peel of durian fruit,which promotes the fruit to reach the ripe state.Therefore,it is of great significance to study the mechanism of pericarp cracking and flesh softening of durian after harvest for prolonging the fresh life of durian fruit.Polygalacturonase(PG)can catalyze the hydrolysis of 1,4-a-D galactoside bonds in pectin,resulting in degradation of pectin and affecting cell wall structure.So far,the function of PG gene has been studied in many species,and it is found that PG gene is mainly involved in fruit ripening and softening,organ shedding,fruit pod dehiscence and other processes,but there is no report on the identification of PG gene in durian.Therefore,this study conducted genome-wide identification,bioinformatics analysis and gene expression analysis of durian PG gene family.In addition,this study also explored the tissue specificity of ethylene synthesis in durian during the ripening process,and compared the pectin structure changes in durian pericarp and flesh before and after fruit cracking.The main results obtained are as follows:A total of 57 PG gene members were identified from durian genome.The protein length of DzPG gene family members ranged from 266 to 609 aa,the molecular weight ranged from 28.79 to 65.05 kDa,and the isoelectric point ranged from 4.58 to 9.59.Protein domain analysis showed that 38 DzPG members contained four typical conserved domains(Ⅰ-Ⅳ,SPNTDGI,GDDC,CGPGHG,RIK).Phylogenetic analysis and gene structure analysis showed that the PG family genes of durian,Arabidopsis thaliana,Solanum lycopersicum,Oryza sativa were divided into seven subfamilies,and the gene structure and Motif distribution of the same subfamily were similar.57 PG genes were distributed in 23 scaffolds,which contained 5 tandem duplication pairs and 36 fragment duplication pairs.Interspecific collinearity analysis showed that durian was most closely related to Arabidopsis thaliana,containing 48 pairs of homologous genes.Transcriptomic results showed that DzPG1,DzPG3,DzPG4,DzPG13,DzPG41,DzPG54 and DzPG49 were all expressed in durian flesh,and the expression level of DzPG1/DzPG3/DzPG4 was the highest.In addition,DzPG25,DzPG48 and DzPG49 were highly expressed in the septal tissue,These results suggest that they may be involved in the process of fruit softening and peel cracking respectively.Determination of ethylene release from different durian tissues found.After durian fruit dehiscent,the ethylene released by the diaphragm is the most,so the ethylene produced by the diaphragm may be the main factor promoting fruit ripening and dehiscent.Further study found that during the process of fruit cracking,the PG enzyme activity and pectin solubility of durian pulp and dehiscence were significantly increased.And split the HGA pectin in the diaphragm structure obvious changes have taken place in the durian before and after cracking,the hint of PG in pectin change may be the cause of durian fruit cracking and softening flesh.