Abstract
BackgroundCereal grains, including wheat (Triticum aestivum L.), are major sources of food and feed, with wheat being dominant in temperate zones. These end uses exploit the storage reserves in the starchy endosperm of the grain, with starch being the major storage component in most cereal species. However, oats (Avena sativa L.) differs in that the starchy endosperm stores significant amounts of oil. Understanding the control of carbon allocation between groups of storage compounds, such as starch and oil, is therefore important for understanding the composition and hence end use quality of cereals. WRINKLED1 is a transcription factor known to induce triacylglycerol (TAG; oil) accumulation in several plant storage tissues.ResultsAn oat endosperm homolog of WRI1 (AsWRI1) expressed from the endosperm-specific HMW1Dx5 promoter resulted in drastic changes in carbon allocation in wheat grains, with reduced seed weight and a wrinkled seed phenotype. The starch content of mature grain endosperms of AsWRI1-wheat was reduced compared to controls (from 62 to 22% by dry weight (dw)), TAG was increased by up to nine-fold (from 0.7 to 6.4% oil by dw) and sucrose from 1.5 to 10% by dw. Expression of AsWRI1 in wheat grains also resulted in multiple layers of elongated peripheral aleurone cells. RNA-sequencing, lipid analyses, and pulse-chase experiments using 14C-sucrose indicated that futile cycling of fatty acids could be a limitation for oil accumulation.ConclusionsOur data show that expression of oat endosperm WRI1 in the wheat endosperm results in changes in metabolism which could underpin the application of biotechnology to manipulate grain composition. In particular, the striking effect on starch synthesis in the wheat endosperm indicates that an important indirect role of WRI1 is to divert carbon allocation away from starch biosynthesis in plant storage tissues that accumulate oil.
Highlights
Cereal grains, including wheat (Triticum aestivum L.), are major sources of food and feed, with wheat being dominant in temperate zones
The weights of mature grains of An oat endosperm homolog of WRI1 (AsWRI1)-wheat were reduced by 29% in the line with 12 inserts but were not affected in the other homozygous lines, as compared to the null lines (Fig. 2a)
Reallocation of carbon from starch to oil in wheat endosperm This study shows that oil accumulation can be initiated and greatly increased in the wheat endosperm by expressing the transcription factor WRINKLED1, it is not a simple redistribution of fixed carbon towards oil
Summary
Cereal grains, including wheat (Triticum aestivum L.), are major sources of food and feed, with wheat being dominant in temperate zones. These end uses exploit the storage reserves in the starchy endosperm of the grain, with starch being the major storage component in most cereal species. Small amounts of oil (triacylglycerols; TAG) are stored in the embryo and aleurone cells that, together with minor amounts in the starchy endosperm, contribute to a total lipid content of approximately 3% of grain dw [3]. Oats (Avena sativa) is unique among cereals in storing significant amounts of oil (up to 18% by grain dw) most of which is deposited in the starchy endosperm [4,5,6,7]. It is of interest to explore strategies to modify carbon allocation to increase the oil content of the starchy endosperm
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