Screening Of Sugar Transport Related Genes In Sand Pear Fruit Based On Transcriptome

The fruit of pear is a kind of storage organ with economic value,and the sugar in the fruit is the main determinant of quality and sensory characteristics.Sugar transporter protein(STs)plays an important role in plant growth and development,mainly mediating the operation of sugars and participating in the loading and unloading of carbohydrates between source and reservoir tissues.Sugar is biosynthesized in the mesophyll cells of leaves and then transported through the phloem to organs such as fruits,seeds,roots and flowers.After long-distance phloem transport,sugars are unloaded from the sieve element�companion cell complex into the surrounding cell wall matrix apoplasmically.The apoplasmic pathway is usually coupled to sugar transporters(STs)to facilitate the movement of sugar across membranes.Thus,identification of ST genes involved in fruit sugar accumulation and understanding their molecular regulatory mechanisms will play a significant role in improving pear sensory quality.This research with three sand pear varieties Pyrus pyrifolia�Cuiguan',the Pyrus pyrifolia�Huanghua'and the Pyrus pyrifolia�Wonhuwang'as test materials,to study the accumulation of several major soluble sugar contents in the development of sand pear fruit,identify and screen the sugar transport related genes in sand pear fruit by transcriptome sequencing technology,and use real-time fluorescence for the selected sugar transport related genes,at the same time,the relative expression of sugar transporter gene was correlated with sugar level.The main research results are as follows:1.With the development of the sand pear,the total sugar content of the three sand pear fruits showed an upward trend.In the early stage of fruit growth,the accumulation rate of total sugar was slow,and in the middle stage of fruit growth,the accumulation rate of total sugar was the fastest,and in the later stage of fruit growth,the accumulation rate of total sugar was slow.The content of fructose is the highest,followed by glucose and sorbitol,and sucrose is the lowest.2.During the fruit development of the three sand pear varieties,there were differences in the accumulation rules of several major soluble sugars.Sorbitol accumulated rapidly in the early stage of fruit development,slowed down in the middle stage of fruit development,and increased slightly in the late stage of fruit development in the three pear varieties;Three sand pear varieties of glucose and fructose accumulation pattern similar to slower the accumulation of early fruit development,the accumulation rate is accelerated,mid late accumulation rate showed a trend of slow,the accumulation of fructose in�Cuiguan'is different from the other two varieties,in the medium term accumulation rate is accelerated,the late accumulation rate to achieve the fastest;The sucrose accumulation rules of the three sand pear cultivars were consistent,and the accumulation rate of fruit development was slow in the first and middle stages,and reached the highest in the later stages.3.By transcriptome sequencing technology,a total of 3.95�10~8~4.61�10~8double-ended short sequences(original short sequences)with a size of about 150 bp were obtained in each library.By filtering the original short sequences through the software,3.52�10~8~4.19�10~8 high quality short sequences were obtained in each library.High-quality short sequences were compared to the pear reference genome,and42196 transcripts were obtained,accounting for 98.58%of the total number of model genes.Based on transcriptome data,118 sugar transporters(STs),including 7sucrose/H+cotransporters or sucrose transporters(SUCs or SUTs),19 sugars will eventually be exported transporters(SWEETs),and 92 monosaccharide transporters(MSTs),were identified by evolutionary tree clustering analysis.4.Through the analysis of the expression profile of the highly expressed sugar transporter protein,a total of 30 ST genes were expressed in the fruit of�Cuiguan',and their expression profile could be divided into three main clusters.Cluster A consisted of1 SWEET and 9 MST,and was upregulated with the development and maturation of fruits.Cluster B with 1 SWEET and 5 MST was down-regulated at all stages of fruit development,while cluster C,including 3 SUC and 11 MST,was up-regulated from 25d to 55d,and then down-regulated with fruit development;The expression of 32 ST in�Yuanhuang'fruits showed two main expression clusters.Cluster A had 2 SUC,1SWEET and 9 MST,and showed up-regulated expression when the fruit was mature.Cluster B was composed of 2 SUC,1 SWEET and 17 MST,and was down-regulated during the fruit development;In�Huanghua',32 ST were expressed,showing two main clusters.Cluster A with 2 SUC,1 SWEET and 12 MST showed up-regulated expression of fruit development,while cluster B with 2 SUC and 15 MST was down-regulated during fruit development.Combined with the expression profiles of three pear varieties.3 SUC and 23 MST proteins were highly expressed in three sand pear varieties.Combined with the expression profiles of the three sand pear varieties,there were 3SUC and 23 MST genes with high expression in the three pear varieties.Eleven genes were identified by qRT-PCR,and all ST genes showed a similar trend to transcriptome data.All ST genes except Pbr031281.1 had significant correlation(r>5.0).5.By analyzing the correlation between sugar transporter gene expression and sugar level,we found that the relative expression level of 10 genes was significantly correlated with the content of soluble sugars(sorbitol,fructose,glucose and sucrose).This indicates that these genes play an important role in the transport of sugar and are responsible for the transfer or transfer of sugar.These ST genes can be considered to be important candidate genes involved in the transport of sorbitol,sucrose,hexose or pentose sugars and their accumulation in sand pear fruit.