COTTON Plants Transformed with A Castor Diverged FATTY ACID Desaturase (FAD2) HAVE Reduced Oil Content and Embryo SIZE

Abstract

Gossypium hirsutum L. variety Coker 312 was transformed by a modified Agrobacterium-mediated procedure using embryogenic cell lines.  A binary plant transformation vector was engineered to contain the cotton alpha globulin promoter (1.1 kb) upstream from the codon optimized castor hydroxylase coding region (~1 kb) for seed specific expression.  Over two dozen primary transgenic plants (T0) were generated (confirmed by PCR).  Non-invasive seed oil analysis by 1H-NMR of T1 transgenic (progeny) seeds of nine independent transgenic events showed significantly reduced seed weight and lowered oil content compared to that of control non-transgenic Coker 312 cotton seeds. Furthermore, in some cases the T1 seeds had shrunken or aborted embryos, suggesting a deleterious effect from the seed-specific, heterologous expression of the castor diverged FAD2. The normal fatty acid composition of cotton seed oil is about 26% palmitic (16:0), 2% stearic (18:0), 15% oleic (18:1) and 55% linoleic (18:2) acids. However, the fatty acid profiles of transgenics, revealed a substantially elevated percentage in oleic acid content relative to non-transgenic Coker 312 (up to 38%) at the expense of linoleic content (reduced to 38%), indicating that expression of the castor diverged FAD2 had interfered with endogenous FAD2 activity reducing flux from oleic acid to linoleic acid.