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Title: Soybean plastidal omega-3 fatty acid desaturase genes GmFAD7 and GmFAD8: structure and expression

Author
item Upchurch, Robert
item Ramirez, Martha

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2011
Publication Date: 8/1/2011
Citation: Upchurch, R.G., Ramirez, M.E. 2011. Soybean plastidal omega-3 fatty acid desaturase genes GmFAD7 and GmFAD8: structure and expression. Crop Science. 51:1673-1682.

Interpretive Summary: We determined the gene structures of soybean chloroplast desaturases FAD7 and FAD8 and the sequence of the protein products encoded by these genes. The FAD7 and FAD8 proteins are enzymes that convert linoleic to linolenic acid in chloroplast membranes, a process that is very important in the mechanisms of adaptation to temperature fluctuations, drought, wounding, and pathogen attack in plants. We found that there were two copies on different chromosomes of each gene in the soybean genome. We measured the expression of the genes in response to temperature. GmFAD7 expression in leaves remained at a relatively low level, and was unaffected by any of the temperature treatments we imposed, but GmFAD8 transcript accumulation was sharply upregulated by a cool temperature (20/16 degrees C) after a 12 h exposure and total a-linolenic as a percent of total leaf fatty acids increased from 60 to about 68% after 48 h exposure to the cool temperature. We measured the expression of the genes in response to pathogen attack. Inoculation of soybean leaves with the fungal pathogen C. kikuchii differentially upregulated the level of GmFAD7 transcripts to twice that of GmFAD8 by 12 h post inoculation. Our findings for soybean, when compared and contrasted with FAD7 and FAD8 data from other plants were, in most respects, highly similar.

Technical Abstract: The genomic structure and deduced protein sequence of soybean FAD7 and FAD8 have features similar to higher plant plastidal '-3 desaturases: 8 exons and 7 introns, predicted proteins of 453 amino acid residues containing three conserved histidine motifs, amino terminal chloroplast transit peptides, and molecular masses of 51.3 and 51.4 kDa, respectively. GmFAD7 has 76% amino acid sequence similarity to GmFAD8. Two complete copies of GmFAD7, one on chromosome 18 and one on chromosome 7 and two complete copies of GmFAD8, one on chromosome 3 and one on chromosome 1 of the Williams 82 soybean genome were found with strong sequence similarity to GmFAD7 and GmFAD8 of cultivar Dare. Dare GmFAD7 transcript expression in leaves remained at a relatively low level, and was unaffected by any of the temperature treatments we imposed, but GmFAD8 transcript accumulation was sharply upregulated by a cool temperature (20/16oC) after a 12 h exposure and total a-linolenic as a percent of total leaf fatty acids increased from 60 to about 68% after 48 h exposure to the cool temperature. Inoculation of soybean leaves with the fungal pathogen C. kikuchii differentially upregulated the level of GmFAD7 transcripts to twice that of GmFAD8 by 12 h post inoculation. Our data for soybean, when compared and contrasted with FAD7 and FAD8 data from other plants was found to be, in most respects, highly similar.