Plant & Animal Genomes XIV Conference

January 14-18, 2006
Town & Country Convention Center
San Diego, CA

Harmonized Diploidization Process Revealed In The Recently Triplicated Brassica rapa Genome: One To Three And Three For One

Tae-Jin Yang¹ , Jung Sun Kim¹ , Soo-Jin Kwon¹ , Beom-Soon Choi¹ , Ki-Byung Lim¹ , Mina Jin¹ , Jin-A Kim¹ , Jee Young Park¹ , Myung-Ho Lim¹ , Ho-Il Kim¹ , Seog Hyung Kim¹ , Yong Pyo Lim² , Beom-Seok Park¹

¹  Brassica Genomics Team, National Institute of Agricultural Biotechnology (NIAB), 224 Suinro Gwonseon-gu, Suwon, Gyeonggi-do, 441-707, Republic of Korea

²  Chungnam National University, Daejeon, 305-764, Republic of Korea

The sequence comparison of five homologous B. rapa BAC clones and their counterparts in Arabidopsis revealed 1) genome duplication in the Arabidopsis-Brassica clade (30-35 MYA), 2) Arabidopsis-Brassica split (17-19 MYA), 3) genome triplication in Brassica (12-17 MYA), and 4) large segmental duplication in B. rapa (1 MYA). During the last 19 million years of evolution, Arabidopsis remained conserved without significant deleterious change but with various insertions. On the other hand, the triplicates of Brassica had large but harmonized deletions and little increase of insertions, resulting in a 0.4-0.8 fold reduction of each collinear sequence. Overall, a genome triplication and the following diploidization process resulted in no gene loss and a 1.8-2.4 fold increase in the genome size of B. rapa. Deleterious events harmonized by functional selection force resulted in returning 88% of the triplicate genes to singlet (44%) or doublet (44%). This study showed that the dynamic and harmonized diploidization process caused by the genome multiplication was probably the driving force for the explosion of the tribe Brassiceae comprising ~240 species during the last 12 million years.