Studies On Gene Expression Of Brassica Polyploid Seeds

Polyploidization is a universal phenomenon in plants and plays a crucial role in evolution.In the process of polyploidization,a series of genomic changes such as DNA loss,homologous recombination,gene transformation and DNA methylation occur to overcome the incompatibility caused by allopolyploid.In recent years,many researchers have studied gene expression changes in various polyploid plants.As an important oil crop,rapeseed plays an important role in human life.High-throughput sequencing has been widely used in the field of omics in recent years.In this study,the transcriptome of two developmental seeds of synthetic Brassica hexaploid with clear parental relationship and its parent(B.rapa and B.carinata)were analyzed by high-throughput sequencing to study the gene expression changes in the seeds and the accuracy of sequencing results was verified by fluorescence quantitative PCR.As a result,a total of 805116806 reads were sequenced and 40142 genes were matched.The differentially expressed genes were identified according to the standard of foldchange?5 and Padj?0.05.After identification,there were 2,085 DEGs between Brassica hexaploid and B.rapa,and 1,265 DEGs between Brassica hexaploid and B.carinata.Similarly,there were 2,649 DEGs and 1,491 DEGs,between Brassica hexaploid and B.rapa and B.carinata,respectively.Most of the DEGs were upregulated in hexaploid seeds compared to its parents.At the mature stage,the hexaploid seeds showed a greater difference from its parents.These identified DEGs had a wide range of functions,which may account for the physiological and morphological differences between Brassica hexaploid and its parents.Through GO annotation,it was found that genes related to "metabolic process","cellular process" and "stimulus response" were highly expressed in hexaploid seeds.The KEGG pathway analysis revealed that hexaploid seeds had higher levels of expression of genes involved in metabolic pathways,RNA transport and biosynthesis of secondary metabolites,and the expression levels in photosynthesis-related pathways were significantly higher than those in B.rapa.Moreover,the putative transcription factor genes such as G2-like,MYB and mTERF were highly expressed in hexaploid seeds,possibly promoting their resistance to stress.There were 378 non-additive genes and 1011 non-additive genes in Brassica hexaploid seeds at full-size stage and at mature stage,respectively.The transgressive expression was the main non-additive expression pattern of Brassica hexaploid.The gene expression difference between the Brassica hexaploid and its paternal parent was more significant than that with its maternal parent,which may be due in part to the cytoplasmic and maternal effects.At the two stages of the seeds in Brassica hexaploid,the number of expressed genes decreased significantly at the mature stage,which was consistent with the decreased physiological activity.In addition,a total of 6001 differentially expressed genes were identified in the two stages of Brassica hexaploid seeds,among which 4,505 genes were down-regulated.At the later stage of maturation,genes related to maturation were expressed in high abundance to regulate seed maturation,including promote chlorophyll degradation,RFO and LEA protein accumulation,etc.Through the study studies on gene expression of seeds of Brassica polyploid and its parents,we have a deeper understanding of gene expression changes of polyploid plants.Our results may provide valuable insights into the adaptation mechanisms of polyploid plants.