Transcriptionomic Analysis Of Heterosis In Cucumber Yield

Heterosis refers to the phenomenon that hybrid offspring are superior to parents in heredity and some growth traits.By cross breeding to increase crop yield is one of the ways to utilize heterosis.Heterosis breeding is widely used in cucumber breeding and significantly increases the yield of cucumber.In order to investigate the formation factors of heterosis in cucumber yield,the monoecism plant D0708-2 was used as the male parent,and hybridized with the female parents gynoecious D1158♀-2,gynoecious D1104-2-4,predominant female lines D1101-1-2,and monoecious plant D0528-2,respectively.Four hybridized combinations were produced by constant parent regression,and through analyzing hybrid performance,investigating relevant field traits and physiological indices,as well as calculating the degree of heterosis,a group of hybridized combination D1104-2-4×D0708-2 with the advantage of over-high parent yield heterosis was determined.Furthermore,During the early-fruit stage,RNA-Seq sequencing technology was used to transcriptome sequence the parents and F1 of this combination and analyzed the transcription differences between parents and F1.By GO classification,KEGG pathway analyzing the different expression gene and explained which genes were involved in the formation of heterosis in cucumber at early-fruit stage.The WGCNA and GSEA were used to further identify the genes which associated with yield dominance.The results of this study are as follows:(1)Correlation analysis of field traits showed that the yield and growth advantages of F1 were related to female flower number and so on.Through redundant analysis,it was found that plant height,middle stem diameter,female flower number and female flower node rate were significant factors affecting yield.(2)The transcriptome sequencing found that the similarity in level of transcription between F1 and female parent at the early-fruit stage was 0.977,which was significantly higher than that of the male parent(0.851).Different samples’ DEGs(Different Expression Gene set)analysis showed that compared F1 with hybridized combination parents,471 significantly up-regulated DEGs and120 significantly down-regulated DEGs in the female parent;933 significantly up-regulated DEGs and 1780 significantly down-regulated DEGs in the male parent.2413 significantly up-regulated DEGs and 821 significantly down-regulated DEGs in the different expression gene of the female and male transcripts.(3)GO classification and KEGG pathway analysis showed that the different expression genes between F1 and parents were mainly enriched in ascorbic acid metabolism,aldehyde acid metabolism,biosynthesis of secondary metabolites,flavonoid biosynthesis,degradation oflimonene and terpene,metabolic pathways,phenylpropanol biosynthesis,plant hormones signal transduction pathways,plant-pathogen interaction,RNA polymerase,biosynthesis of sesquiterpene and triterpenoid,toluylene,diarylheptanoids and gingerol biosynthesis,flavone and flavonol biosynthesis,isoflavone biosynthesis,plant MAPK signaling pathway and so on.(4)By WGCNA analysis finding a gene module related to cucumber yield.The GSEA analyzing showed that there were significant differences in the enrichment between F1 and parents in plant hormone signal transduction pathway,glycolysis pathway and carbon metabolism.Among them,the pyruvate dehydrogenase(ace E)and pyruvate dehydrogenase complex E2(ace F)were highly expressed in the female parent.The hormone-associated proteins of abscisic acid receptor(PYL4)and gibberellin receptor(GID1b)were higher expressed in F1.Meanwhile,the key enzymes such as 6-phosphogluconase and malic dehydrogenase related to tricarboxylic acid cycle in the male parent were enriched and expressed,while there was no significant enrichment in F1.That indicated that gibberellin(GA)and abscisic acid(ABA)in F1 may inhibit the glycolytic pathway,thereby increased the accumulation of sugar.And the higher activity hormones such as ABA and GA may by inhibiting respiration to reduce the consumption of organic matter in the body.This model may be the basis for the formation of F1 production advantages.