Comparative Heterosis Analysis Of Brassica Oleracea L. Var. Capitat Based On Transcriptome Data Of Cabbage Head Leaves

The research of plant heterosis began more than a hundred year ago.However,the genetic mechanism of heterosis still unclear.Thus we selected two varieties of cabbage F₁generations and their parents.Nine horticultural traits were surveyed and statistics.The mid-parent heterosis and high-parent heterosis were calculated separately.At the same time,we compared different groups of the DEGs between hybrid and their parents,discussed mostly enriched biological functions and metabolism pathways of the heterosis-related DEGs.In addition,we also characterized the gene expression patterns in hybrids and analyzed cis and trans-regulation which regulate gene expression in hybrids.Finally,to reveal the molecular regulation mechanisms of gene expression in hybrids,we analyzed the effects of allelic regulation on the gene expression inheritance patterns in hybrids.The main results are as follows:1.The analysis of horticultural traits showed that the head weight was higher than the other horticultural traits in MPH and HPH,ie,the yield heterosis is obvious.Furthermore,the RNA-seq technique was used to analyze the DEGs and it was found that the DEGs between the two F₁ generations and their maternal parents were significantly less than the DEGs between their paternal parents,which indicate a more similar gene expression profile between female parent and the F₁ generation.Volcano map and MA map showed that the differential fold of the up-regulated genes was significantly higher than that of the down-regulated genes,indicating the up-regulated genes play a major role in gene differential expression.2.Pathway enrichment analysis revealed that the DEGs between hybrid and their parents mainly involved in growth and development?Biological process?,carbohydrate transport and metabolism?G?,signal transduction?T?,and amino acid synthesis,transport,and metabolism?E?,etc.These biological functions or metabolic pathways include growth and development related transcription factors of cabbage heads.The alternative splicing analysis found that more than 81%of the alternative splicing events were alternative 5'first exon and alternative 3'last exon?TSS and TTS?,followed by intron retention?IR?,and other alternative splicing events accounted for a smaller proportion.3.The gene expression inheritance patterns of F₁ generation indicated that the maternal-expression level dominance was dominant,followed by the paternal-expression level dominance,and the additive expression was the least.Allele-specific expression?ASE?analysis revealed that cis-and compensating regulation were dominant in HY1 and HY2,respectively,and trans-regulation to gene expression divergence is greater than that of cis-regulation,indicating the important role of cis-and trans-regulations in regulating gene expression in hybrids.4.The allelic variation analysis in HY1 suggested the asymmetric effect that one genome alleles activated by trans-regulatory factors of the other genome.The particular combinations of up and down-regulation of both genome alleles determined each category of expression inheritance of genes.The relative-allele expression?RAE?and ASE distribution in expression inheritance patterns indicate an imbalanced distribution of RAE in any of the expression patterns in the two hybrids and both cis-and trans-regulation are involved in the process of gene expression variation.