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Title: Deletions of the SACPD-C locus elevate seed stearic acid levels but also result in fatty acid and morphological alterations in nitrogen fixing nodules

Author
item Gillman, Jason
item STACEY, MINVILUZ - University Of Missouri
item CUI, YAYA - University Of Missouri
item BERG, HOWARD - Danforth Plant Science Center
item STACEY, GARY - University Of Missouri

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2014
Publication Date: 5/27/2014
Publication URL: http://handle.nal.usda.gov/10113/58926
Citation: Gillman, J.D., Stacey, M.G., Cui, Y., Berg, H., Stacey, G. 2014. Deletions of the SACPD-C locus elevate seed stearic acid levels but also result in fatty acid and morphological alterations in nitrogen fixing nodules. Biomed Central (BMC) Plant Biology. 14:143. DOI:10.1186/1471-2229-14-143.

Interpretive Summary: Soybean oil is the preeminent edible oil in the United States. Despite its widespread use, conventional soybean oil is not ideal for many baking and industrial applications. Mutant lines with altered oil properties have been identified, but only a few have been rigorously studied at the genetic level. Here we report detailed genetic analysis on a number of soybean mutant lines with increased amounts of a normally trace component of soybean oil: stearic acid. Stearic acid (C18:0) is ideal for baking and many industrial applications. Although technically considered a saturated fat, stearic acid has been shown to have no negative impacts on cardiovascular health, unlike trans fats. Our results also identified a previously unknown function for stearic acid metabolism in nitrogen fixing nodules in soybean roots. Mutant lines with elevated stearic acid were found to have altered nodule appearance and a necrotic zone within nodules. Despite the obvious visual differences, nitrogen fixation was unaffected in our laboratory studies. In addition to identifying a new role for stearic acid in nodule formation, our results have dramatically expanded on the genetic resources for effective breeding for elevated soybean seed stearic acid content.

Technical Abstract: Soybean (Glycine max) seeds are the primary source of edible oil in the United States. Despite its widespread utility, soybean oil is oxidatively unstable. Until recently, the majority of soybean oil underwent chemical hydrogenation, a process which generates trans fats. An alternative to chemical hydrogenation is genetic modification through identification and introgression of mutant alleles. We utilized comparative whole genome hybridization and genetic analysis to define radiation-induced lesions in soybean mutants with moderately increased seed stearic acid (10-15% of seed oil). Stearic acid is an oxidatively stable saturated fat with no negative impacts on cardiovascular health. The deletion of one SACPD isoform encoding gene (SACPD-C) was perfectly correlated with moderate elevation of seed stearic acid content. However, SACPD-C deletion lines were also found to have altered nodule fatty acid composition and grossly altered morphology. Despite these defects, overall nodule accumulation and nitrogen fixation were unaffected, at least under laboratory conditions. Although no yield penalty has been reported for this trait, our results demonstrate that genetic alteration of seed traits can have unforeseen pleiotropic consequences. We have identified a role for fatty acid biosynthesis, and SACPD activity in particular, in the establishment and maintenance of symbiotic nitrogen fixation.