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GENOMICS, MOLECULAR GENETICS & BIOTECHNOLOGY

Effect of Temperature on Microsomal Omega-3 Linoleate Desaturase Gene Expression and Linolenic Acid Content in Developing Soybean Seeds

^a Microbiology Dep., North Carolina State Univ., Raleigh, NC 27695
^b USDA-ARS, Soybean and Nitrogen Fixation Unit and Plant Pathology Dep., North Carolina State Univ., Raleigh, NC 27695

^* Corresponding author (greg_upchurch{at}ncsu.edu).

The mechanism of temperature adaptation in plants, including the formation of polyunsaturates in seed storage lipids, most likely involves transcriptional as well as post-translational regulation of fatty acid desaturase activity. The present investigation was conducted to measure changes in the transcript accumulation among the three members of the soybean [Glycine max (L.) Merr.] microsomal omega-3 fatty acid desaturase gene family in response to altered growth temperature during seed development. Microsomal omega-3 fatty acid desaturases catalyze the insertion of a third double bond into linoleic (18:2^{9, 12}) acid to produce linolenic (18:3^{9, 12, 15}) acid. At 35 d after flowering, transcript accumulation (normalized for soybean actin) of GmFAD3A decreased by 5- to 15-fold, GmFAD3B by 2- to 9-fold, and GmFAD3C by 2- to 3-fold in seeds that developed in a warm (day/night [D/N] = 30/26°C) versus a normal (D/N = 26/22°C) or a cool (D/N = 22/18°C) environment. At this stage of seed development, decreased omega-3 desaturase gene expression levels were positively associated with reductions of 39 to 50% in the linolenic acid content of seeds of three soybean varieties examined. Thus, transcriptional regulation of the microsomal omega-3 fatty acid desaturase gene family likely accounts, at least in part, for the reduced linolenic acid levels in soybean seeds grown at elevated temperature.

Abbreviations: bp, base pair • DAF, days after flowering • D/N, day/night • FAME, fatty acid methyl ester • GmFAD3, Glycine max omega-3 fatty acid desaturase • PCR, polymerase chain reaction • RT-PCR, reverse transcription–polymerase chain reaction