Abstract
A combination of lipidomics, transcriptomics and bioimaging has been used to study triacylglycerol synthesis and deposition in the developing starchy endosperm of wheat. The content of TAG increased between 14 and 34 days after anthesis, from 50 to 115 mg/100 g dry wt and from about 35 to 175 mg/100 g dry wt in two experiments. The major fatty acids were C16 (palmitic C16:0 and palmitoleic C16:1) and C18 (stearic C18:0, oleic C18:1, linoleic C18:2 and linolenic C18:3), with unsaturated fatty acids accounting for about 75–80% of the total throughout development. Linoleic acid (C18:2) was the major component at all stages and the proportion increased during development. Transcript profiling indicated that predominant route to TAG synthesis and oil accumulation is via the Kennedy pathway and diacylglycerol acyltransferase (DGAT) activity. Confocal microscopy of stained tissue sections showed that TAG accumulated in droplets which are associated with protein and concentrated in the starchy endosperm cells below the sub-aleurone cells. Transcripts encoding 16kd oleosins were also expressed, indicating that the oil droplets are in part stabilised by oleosin proteins.
Highlights
Wheat is the dominant crop and major staple food in Europe, North Africa, West and Central Asia and North and South America, where it contributes between 20% and 50% of the total calories in the human diet
The global success of wheat is due to its wide adaptability and to the grain processing properties, in particular the ability of wheat flour to be processed into bread, other baked products, pasta and noodles
We report here the first detailed study of TAG accumulation and deposition in the wheat starchy endosperm during the major grain filling period
Summary
Wheat is the dominant crop and major staple food in Europe, North Africa, West and Central Asia and North and South America, where it contributes between 20% and 50% of the total calories in the human diet. Wheat lipids are typically minor components of grain, accounting for only 2.5–3.3% of whole grain and 2.6–2.7% of white flour (Chung et al, 2009) They affect the volume and texture of loaves and other baked products (Pycarelle et al, 2019), probably by a combination of effects including binding to and plasticising the gluten network and stabilizing the gas cells which are formed during dough mixing and expanded during fermentation (Salt et al, 2018). We report here the first detailed study of TAG accumulation and deposition in the wheat starchy endosperm during the major grain filling period This is based on the analysis of hand-dissected tissues to avoid lipid transfer between tissues with the lipid profiles being combined with transcript analysis and confocal microscope imaging of tissue sec tions. This study add to our currently limited knowledge of the synthesis and deposition of TAG in the starchy endosperm during grain maturation and provides a basis for determining the contributions of TAGs to flour processing and breadmaking
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