Genome-wide Identification GRAS Gene Family In Brassica Napus

Allotetraploid Brassica napus L.(AACC,4n=38)is a natural hybrid of Brassica rapa(AA,2n=20)and Brassica oleracea(AA,2n=18),and is a model plant for the study the polyploidization.It not only experienced the ancient ??? and ?genome-wide duplication events,but also experienced a Brassica-specific genome-wide tripling event(Bra-? WGT event).The GRAS gene family is a type of transcription factor that has a great influence on plant growth and development,such as signaling transduction,abiotic and biotic stress responses.However,the impact of the Bra-? WGT event and allopolyploidization on Brassica napus GRAS gene family is still unclear,which in turn limits the application of the GRAS gene family in breeding.In this study,we performed a systematic analysis to study the impact of Bra-? WGT event and the allopolyploidization on Brassica napus on the GRAS genes of Brassica species based on the complete identification and comprehensive analysis.The main results are as follows:(1)96 GRAS genes were identified in Brassica napus,we divided them into 13 different subfamilies and 17 OGs(orthologous groups).Compared with other species,the members of 4 subfamilies and 12 OG were lost in evolution.PAT and LISCL subfamilies have been significantly expanded after Bra-? WGT event and allopolyploidization,while LS and NSP1 subfamilies tend to be expand-resistant.(2)Analysis of gene structure and protein conserved motifs revealed that the members of the GRAS gene family of Brassica napus are relatively conserved in gene structure.The genetic structure of each member within each subfamily was highly similar,but there existed some differentiation between each subfamily.After allopolyploidization,some of the Bna GRAS genes generate new introns compare to the homologous genes in their ancestral species,but most of the GRAS gene structures still retain single exons or only one intron.(3)After allopolyploidization,the chromosomal location of most GRAS genes inBrassica napus is highly similar with that of its ancestral species,and this feature can be used to predicting the chromosomal localization of GRAS that not precisely determined in genomic annotation files.On the other hand,it was also found that the homologous genes of two Brassica rapa GRAS genes were located in the Cn subgenome of Brassica napus,which may be caused by homologous exchange.(4)By analyzing the transcriptome data,GRAS gene is widely involved in the growth and development of many tissues,but some genes show different tissue-specific expression between B.napus and their ancestors.The GRAS genes also involved in many responses in biotic stress and abiotic stress.(5)Brassica napus GRAS genes were under purified selected in the evolution,and the neofunctionalization were not detected.Most of the GRAS genes are very conservative in evolution.