Identification And Analysis Of Different Cultivars Of Apple Fruit Cell Morphology And XTH Gene Related To Development

Apple(Malus domestica Borkh.)is one of the most important fruits at home and abroad and an important fruit tree species in China.Excellent texture quality has become one of the basic conditions for apple main cultivars.The texture of apple pulp is related to cell morphology and cell wall structure characteristics.Xyloglucan glycosyltransferase/hydrolase(XTH)is a key enzyme that regulates cell wall relaxation and cell growth.In this study,apples of different texture types cultivars and hybrids were used as materials,and apple texture was assessed by instrumental tests and sensory evaluations.Ultrastructure of the fractured surface of pulp was observed and compared using scanning electron microscopy.On this basis,some representative cultivars were selected to identify the expression of the XTH gene family in the apple genome.The main results obtained are as follows:1.There was a positive correlation between juice and crispness;there was a negative correlation between pulp thickness and hardness,and a positive correlation with crispness.The cells of the high-crispness cultivars were well-arranged,with no large cell gaps,no obvious deformation of the fracture surface.The fractures were smooth and tidy with brittle fractures,and almost no plastic deformation of the cell wall at the time of fracture;the cells of the low-crispness cultivars were disordere,and there are large gaps between cells,and the production of ductile fractures,the fracture can see the fiber area and the cut lip area,showing fibrous and hairy-like,showing ductile fracture.The soft cultivars are larger than the hard pulp cells.2.Thirty-two XTH genes were identified from the apple genome database and named according to their position on the apple's chromosomes.Based on the phylogenetic tree,the apple XTH family was divided into five subgroups I,II,IIIA,IIIB and IV.There are exon-intron increases or deletions and gene length changes,for example,MdXTH16 has 4 fewer exons than its homologue MdXTH21,etc.3.During the fruit growth period,XTH were expressed in the 70 th to 112 th days after the full-bloom stage which is the period of fruit enlargement.During the Qinguan's fruit storage period,five genes in the IIIA subgroup expressed on the entire storage period.It is considered that it is related to the softening of fruit storage period.Apple XTH genes on subgroups I are associated with auxin responses.Apple XTH genes on subgroups II are associated with powdery mildew stress response.The two genes,MdXTH6 and MdXTH24,are responsive to drought and salicylic acid treatment and are related to plant drought resistance.