Abstract
Maize (Zea mays) oil has high value but is only about 4% of the grain by weight. To increase kernel oil content, fungal diacylglycerol acyltransferase2 (DGAT2) genes from Umbelopsis (formerly Mortierella) ramanniana and Neurospora crassa were introduced into maize using an embryo-enhanced promoter. The protein encoded by the N. crassa gene was longer than that of U. ramanniana. It included 353 amino acids that aligned to the U. ramanniana DGAT2A protein and a 243-amino acid sequence at the amino terminus that was unique to the N. crassa DGAT2 protein. Two forms of N. crassa DGAT2 were tested: the predicted full-length protein (L-NcDGAT2) and a shorter form (S-NcDGAT2) that encoded just the sequences that share homology with the U. ramanniana protein. Expression of all three transgenes in maize resulted in small but statistically significant increases in kernel oil. S-NcDGAT2 had the biggest impact on kernel oil, with a 26% (relative) increase in oil in kernels of the best events (inbred). Increases in kernel oil were also obtained in both conventional and high-oil hybrids, and grain yield was not affected by expression of these fungal DGAT2 transgenes.
Highlights
Maize (Zea mays) oil has high value but is only about 4% of the grain by weight
Small but statistically significant increases in maize kernel oil were achieved by expression of fungal diacylglycerol acyltransferase2 (DGAT2) transgenes using an embryo-enhanced promoter
A DGAT2 gene isolated from N. crassa encoded an enzyme with somewhat greater activity in maize kernels than the enzyme from U. ramanniana, and expression of the S-NcDGAT2 transgene resulted in greater increases in maize kernel oil
Summary
Maize (Zea mays) oil has high value but is only about 4% of the grain by weight. To increase kernel oil content, fungal diacylglycerol acyltransferase (DGAT2) genes from Umbelopsis (formerly Mortierella) ramanniana and Neurospora crassa were introduced into maize using an embryo-enhanced promoter. YLEDON1 (ZmLEC1) in maize increased kernel oil by up to 48% (Shen et al, 2010) This transcription factor produced negative pleiotropic effects, including reduced seed germination and leaf growth. Overexpression of a transcription factor downstream of ZmLEC1, maize WRINKLED1 (ZmWRI1), resulted in similar increases in kernel oil but without any detectable off types (Shen et al, 2010). DGAT2 has little sequence similarity to DGAT1 and is part of a family of proteins that transfer acyl groups from CoA to neutral lipids (Lardizabal et al, 2001; Turkish and Sturley, 2007) Whether these two classes of DGATs have redundant or specific functions in TAG biosynthesis in plants is not clear. Fungal DGAT2 Increases Maize Oil fungal species has been shown to increase seed oil content in Arabidopsis (Arabidopsis thaliana; Jako et al, 2001), soybean (Lardizabal et al, 2008), and maize (Zheng et al, 2008)
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