Comparative Study On Pattern Of Fatty Acid Biosynthesis And Sequences Of Related Genes Cloned In Oilseed Crops

Oil content and fatty acid composition are the key indicators of seed quality of oil crops. In this study, several key genes (fad2, fad3, fad7, bccp, pepck and pepc) involved in the biosynthesis of fatty acids were cloned in oil crops including rapeseed, soybeans, sesame and peanuts. And the gene sequences were analyzed by bioinformatic tools to characterize the nucleic acid and protein in relevance to their structure and function. The results are highly significant in the study of origin and evolution of these oil crops. On the other hand, the author also studied the fatty acid accumulation pattern of these oilseed crops during their seed development. It is designated to reveal at the molecular level the genetic mechanism of oil content and fatty acid composition by combining the gene sequence information. The results of this study will be significant either in genetic engineering, molecular marker-assisted breeding or in elucidation of crop evolution and classification.In this study, 26 sequences of fad2, fad3, fad7, fael, bccp, pepc and pepck genes were successfully isolated from rapeseed, soybean, sesame and peanut by using the methods of homologous sequence and Genome Walking. Among the sequences isolated, the pepck gene fragment from peanut and the fad7 genome sequence from sesame have not yet been reported in the Genbank. Bioinformatics methods were used in this study to analyze these sequences in order to characterize the genes in DNA and protein level and to reveal their differences among crops. Through further analysis of the protein functional domain in fael genes isolated from high erucic acid variety Zhongyou 821 and low-erucic acid variety Zhongshuang NO.9 of Brassica napus, it was found that it is lack of the conservative Gly457 sites of ACP_syn_â…¢_C functional domain that Zhongshuang NO.9 obtained low erucic aicd trait, which is different from other low-erucic acid varieties. This discovery gives a new theoretical support to Lu Chang-ming' view that fael gene of Zhongshuang NO.9 harbers a frameshift mutation resulting in the loss of activity of FAE1 enzyme.Study of fatty acid accumulation pattern in seed development of the four oil crops revealed that the cumulative process of linoleic acid in rapeseed looked unique from soybean, peanut and sesame. It is considered that this phenomenon is attributed to the structural change of the second conservative His motif of the secondary structure in FAD2 enzyme. In this experiment, we failed to isolate fad3 genes from peanut and sesame though repeated endeavour was made and thus proposed that the fad3 gene may not exist in the peanut and sesame, which migh be the reason for the absence of linolenic acid in these species. No erucic acid was detected during the seed development of soybean, peanut and sesame in accordance with the finding that no fael gene was isolated from these species.In conclusion, fatty acid accumulation patterns were formulated and the key genes for the pattern were isolated and analyzed in four major Chinese oilcrops. It will provide a theoretical basis for the oilseed quality breeding in future.