Identification and expression analysis of key enzyme gene family in lemon sucrose metabolism

【Objective】 The purpose of the study was to identify the members of the key enzyme gene family of lemon sucrose metabolism and analyze their expression during fruit development in two lemon cultivars with obvious differences in sucrose accumulation, so as to provide reference for revealing the role of lemon sucrose metabolic key enzyme in fruit development and the molecular mechanism of sucrose metabolism in lemon and other citrus fruits.【Method】 Bioinformatics methodwas used to identify the gene family members of the key enzymes of lemon sucrose metabolismsucrose synthetase(SUS), sucrose phosphatesynthase(SPS), sucrose invertase(INV), and their basic physicochemical properties, conserved motifs, gene structures, phylogeny, protein-conserved functional domains, cisacting elements and evolutionary mode were comprehensively analyzed. The expression patterns of the gene family members of key enzymes of lemon sucrose metabolism in different tissues were analyzed based on transcriptomic data. Real-time fluorescence quantitative PCR(qRT-PCR) was used to detect its expression during peel and pulp development.【Result】 A total of 6 ClSUS gene family members(ClSUS1-ClSUS6), 4 ClSPS gene family members(ClSPS1-ClSPS4) and 15 ClINV gene family members(ClINV1-ClINV15) were identified from the lemon genome, all of which were hydrophilic proteins, among which ClSPSs gene encoded the largest number of amino acids. The numbers and types of conserved motifs encoded by CISUSs, ClSPSs and ClINVs genes were roughly the same, with the number of introns in ClSUSs gene ranging from 12 to 14, the number of introns in ClSPSs gene ranging from 12 to 13, and the number of introns in ClINVs gene ranging from 1 to11. ClSUS gene family members and ClINV gene family members were each divided into 3 subfamilies, and ClSPS gene family was divided into 2 subfamilies. ClSUS6, ClINV1 and ClINV8 proteins all expanded into new structural domains, and ClINV protein family members were divided into two different hydrolase types according to different structural domains. ClSUSs, ClSPSs and ClINVs gene promoter regions all contained hormonal response, light response, stress response and growth and development regulatory elements, and a total of 25 genes were unevenly distributed on chromosomes, resulting in gene tandem and fragment replication phenomenon. Based on transcriptome data analysis, it was found that only 21 genes were expressed, of which 7 genes were specifically expressed in different tissues of lemon. The relative expression of 21 genes was correlated with glucose, fructose and sucrose contents to varying degrees, among which 9 genes were greatly positively or negatively correlated with the contents of lemon glucose, fructose and sucrose. The qRT-PCR results showed that the expression of ClSUSs, ClSPSs and ClINVs genes in the peel as a whole was higher than that in the pulp, and the genes with high expression in the peel were ClSUS4, ClSPS2, ClINV14 and ClINV1, which were speculated to play an important role in the accumulation of soluble sugars in lemon fruit.【Conclusion】 The 25 identified members of the key enzyme gene family members of lemon sucrose metabolism have obvious differences in physicochemical properties and gene structures, and have great tissue expression specificity, and some members such as ClSUS4, ClSPS2, ClINV1 and ClINV14 are the key genes regulating the difference of soluble sugar content between lemon peel and pulp.