Study On The Differences Of Gene Expression Between Pear And Apple Wild Cultivation Materials Based On RNA-seq Technique

Pear and apple are important economic fruits in the world.In order to explore the transcriptional regulation mechanism of pear and apple in the long-term domestication process,this study selected ’Douli’(Pyrus calleryana Dence)and ’Dangshansuli’(Pyrus bretschneideri Rehd),’Xifuhaitang’(Malus micromalus Makino)and ’Golden Delicious’(Malus domestica)as experimental materials,and selected three important stages of fruit development,namely,young fruit stage,swelling stage and mature stage.Transcriptome sequencing was performed on two fruit trees.Pear and apple obtained 14937456-30370082 and 16219542-34807619 reads,respectively.Physiological indices including fruit size,fruit weight and sugar and acid content were determined during the experiment.Differential genes in fruit were identified and bioinformatics was analyzed.Changes in fruit domestication were analyzed from fruit size,flavor,resistance and peel color.The results will provide reference for improvement of cultivars and utilization of wild resources.The main results are as follows:1.The main physiological indexes of pear and apple were obtained.The single fruit weight of mature ’Dangshansuli’ was 447 times of that of ’Douli’,and its horizontal and vertical diameter was 8.4 times of that of ’Douli’.The single fruit weight of mature ’Golden Delicious’ was 8.12 times of that of ’Xifuhaitang’,and its horizontal and vertical diameter was 2.9 times of that of ’Xifuhaitang’.There are obvious differences in size and quality between cultivated species and wild species.The fruit size and quality of cultivated species were much larger than that of wild species.The total sugar content of cultivated varieties was higher than that of wild species,and the total acid content was lower than that of wild species.In addition,the content of glucose,fructose and sucrose increased with the development of fruits,which was positively correlated with the total sugar content.2.Identification of differentially expressed genes.There were 3339,4005 and 4070 differentially transcripts in young fruit stage,swelling stage and mature stage of two pear cultivars,respectively.There were 3188,2975 and 3918 differentially transcripts in three stages of two apple cultivars,respectively.With the growth of fruit,the difference between wild and cultivation became more and more obvious,and the difference between young fruit stage and mature fruit stage was the biggest.3.The differential transcripts of pear fruits were mainly enriched in 8 cell components,6 molecular functions and 14 biological processes.The functions of up-regulated transcripts in ’Dangshansuli’ and down-regulated transcripts in ’Douli’ were similar.Biological processes mainly focus on cell division and growth,the development of primary roots,flowers,seeds and other organs,metal ions.These differences explain the differences in fruit size,fruit quality and fruit resistance during long-term domestication.KEGG metabolism of differential transcripts of pear fruits were mainly concentrated in plant hormone signal transduction,glycolysis/gluconeogenesis,starch and sucrose metabolism.In plant hormone signal transduction,the expression of IAA of ’Dangshansuli’ was about 4 times higher than that of ’Douli’,and the SAUR family protein was about 9 times higher than that of ’Douli’.L-lactate dehydrogenase and sucrose synthase that are involved in glycolysis/glyconeogenesis,starch and sucrose metabolism were down-regulated,and their expression was the highest at young fruit stage,and was higher in ’Dangshansuli’ than ’Douli’.Superoxide dismutase Cu-Zn family,acetyl-CoA acyltransferasel were down-regulated,and higher in ’Douli’ than ’Dangshansuli’.4.The differentially expressed genes in apple mainly enrich 8 biological pathways,16 cell components and 6 molecular functions.The main enriched items in biological processes are glycolysis,cytokinin reaction,biological stress response,salt stress response,photosynthesis,etc.Cell components mainly include vacuole membrane,ribosome and chloroplast,and molecular functions mainly focus on ribosome composition,glutathione transferase activity,metal ion activity,L-ascorbic acid activity,etc.KEGG was enriched to 30 pathways,including secondary metabolites synthesis,carbon metabolism,glycolysis/gluconeogenesis,citric acid metabolism,etc.Differential genes in apple were clustered into nine expression modules.The analysis of the relationship between samples and modules showed that black module mainly focused on defense responses to light and cold indicated that the expression of defense genes in the fruit of ’Xifuhaitang’ was significant at the expansion stage;pink at expansion stage of ’Golden Delicious’ concentrates on malic acid metabolism and defense response;Brown at young fruit stage of ’Golden Delicious’concentrates on transcriptional regulation,ion response and sugar catabolism;yellow at maturity stage of ’Golden Delicious’ concentrates on defense response and growth and development biosynthesis reaction;red at maturity stage of ’Xifuhaitang’ concentrates on flavonoid and anthocyanin biosynthesis reaction may explain that the peel color of’Xifuhaitang’ turns red when it ripens.5.Domestication genes of key characters in wild and cultivated fruits.The genes related to fruit size,flavor,resistance and peel color were identified by physiological indices and bioinformatics analysis of different genes.There were 22,32,79 and 10 genes in pear and 27,70,89 and 12 genes in apple,respectively.Fruit size genes are involved in GO:0009735,GO:0015979,fruit flavor genes are involved in GO:0006096,GO:0006633,GO:0009809,fruit resistance genes are involved in GO:0006950,GO:0009607,and peel color genes are involved in GO:0033788,GO:0009813,GO:0009718,etc.