Analysis Of Gene Expression Related To Sugar Metabolism In Watermelon

The type,content,composition proportion and formation dynamics of sugar in fruits are one of the important bases for the formation of fruit flavor.The sweetness of watermelon is the core characteristic that determines the quality of watermelon.The type,content and proportion of sugar accumulated in watermelon fruits determine the taste,quality and commercial value of watermelon.In order to further systematically understand the basic characteristics of genes related to sugar metabolism in watermelon and the accumulation mechanism of sugar in watermelon,watermelon high-fructose lines ZXG1455,low-fructose lines ZXG956 and high-sucrose lines W1-1 were used as experimental materials in this experiment.The roots,stems,leaves and flesh of watermelon were taken 14,28 and 42 days after pollination,and RNA was extracted.The contents of sucrose,glucose and fructose in all flesh materials were measured.Based on pre-transcriptome results,four key genes(pyruvate decarboxylase gene Cla018009,fructose diphosphate aldolase gene Cla003902,UDP glucose 6-dehydrogenase gene Cla022014 and 6-phosphofructokinase gene Cla014372)related to sugar metabolism were cloned from watermelon genome.Their sequence characteristics were analyzed,and their expression levels in watermelon fruits and other tissues and their relationship with sucrose,fructose and glucose accumulation during fruit development were studied.The following conclusions were drawn:(1)The W1-1 sucrose content reached the peak at 28 days after pollination,and then decreased.The sucrose content of ZXG1455 decreased during fruit development.The variation trend of sucrose during the development of ZXG956 was similar to that of W1-1.The overall sucrose content was W1-1?ZXG1455?ZXG956.The W1-1 glucose content reached the peak 42 days after pollination.The glucose content of ZXG1455 was similar to that of W1-1 during fruit development.ZXG956 maintains a low level of glucose throughout its development.The overall glucose content was ZXG1455?W1-1?ZXG956.The content of W1-1 fructose reached the peak 42 days after pollination.The fructose content of ZXG1455 reached the peak at 28 days after pollination,and then decreased.The change of fructose content of ZXG956 during fruit development was similar to that of W1-1,but much lower than that of W1-1 and ZXG1455.The overall fructose content was ZXG1455?W1-1?ZXG956.(2)The expression level of the pyruvate decarboxylase gene Cla018009 in flesh of W1-1and ZXG1455 was much lower than that of ZXG956.The expression level of fructose diphosphate aldolase Cla003902 was higher in all three watermelon flesh materials,and the expression level of W1-1 and ZXG1455 was slightly higher than that of ZXG956.The expression levels of UDP glucose 6-dehydrogenase gene Cla022014 and 6-phosphofructokinase gene Cla014372 in flesh of W1-1 were significantly higher than those of ZXG1455 and ZXG956.(3)Tissue specific studies showed that gene Cla018009 had the highest expression in W1-1and ZXG956 flesh materials,and the highest expression in ZXG1455 leaf materials.The expression of Cla003902 gene was the highest in W1-1 and ZXG1455 flesh materials,and the highest in ZXG956 root.The expression level of Cla022014 was the highest in W1-1 flesh material,ZXG1455 leaf tissue and ZXG956 root.The expression level of Cla014372 was the highest in the leaves of W1-1 and ZXG956,and in the flesh of ZXG1455.(4)The coding region of gene Cla018009 was 1815 bp,encoding 605 amino acids.The encoding region of Cla003902 gene was 1173 bp,encoding 390 amino acids.The coding region of gene Cla022014 was 1443 bp,encoding 480 amino acids.The coding region of gene Cla014372 is1365 bp,encoding 454 amino acids.(5)The protein encoded by Cla018009 has a conserved TPP binding site and a pyrimidine binding domain of pyruvate decarboxylase.The similarity between Cla018009 and the protein derived from melon(NP＿001284422.1)is 97.52%.Phylogenetic analysis showed that Cla018009 was highly conserved in Cucurbitaceae.There were conservative Tim-like beta/alpha barrel domains in the protein encoded by Cla003902,and the similarity with the corresponding protein of melon(KAA0046298.1)was as high as 97.95%.The phylogenetic analysis showed that this gene had a high homology in Cucurbitaceae.The protein encoded by Cla022014 has a NAD binding domain and two UDPG＿MGDP domains.The similarity between the Cla022014 protein and the protein of melon(KAA0064755.1)was 93.33%.Phylogenetic analysis showed that the Cla022014 protein had a high homology with the corresponding protein of melon(XP＿038884083.1),relatedness to other species was very low.The protein encoded by Cla014372 had some conserved regions,such as the binding site of fructose 1,6-diphosphate,the binding site of pyrophosphate and the interaction surface of dimer.The similarity with the corresponding protein of cucumber(XP＿004134815.1)was the highest,which was 93.61%.The ATP-dependent6-phosphofructokinase of watermelon,cucumber,muskmelon and balsam melon,all of which belong to the cucurbitaceae,was highly homologous,but had relatively distant relationship with the corresponding proteins of other species.There was no difference in the genes coding region and corresponding protein of Cla018009,Cla003902 and Cla022014 from the three watermelon materials.There were two differences in Cla014372 gene among the three materials.The reference genome of position 726 was C,and W1-1,ZXG1455,and ZXG956 were T,does not cause amino acid changes;The reference genome,W1-1 and ZXG1455 of position 1267 were G(corresponding to amino acid Glu)and ZXG956 was A(Lys).