Department of Plant Breeding, Swedish University of Agricultural Sciences, SE-23053, Alnarp, Sweden.
Department of Plant Sciences, Rothamsted Research, Harpenden, AL5 2JQ, UK.
BMC Plant Biol. 2020 May 25;20(1):235. doi: 10.1186/s12870-020-02438-9.
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. 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.
An 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 C-sucrose indicated that futile cycling of fatty acids could be a limitation for oil accumulation.
Our 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.
谷物，包括小麦（Triticum aestivum L.），是食物和饲料的主要来源，而小麦在温带地区占主导地位。这些用途利用了谷物淀粉质胚乳中的储存储备，淀粉是大多数谷类物种的主要储存成分。然而，燕麦（Avena sativa L.）则不同，其淀粉质胚乳储存大量油脂。因此，了解碳在淀粉和油脂等储存化合物组之间的分配控制对于理解谷物的组成和用途质量非常重要。WRINKLED1 是一种转录因子，已知它能诱导几种植物储存组织中的三酰基甘油（TAG；油脂）积累。
来自胚乳特异性 HMW1Dx5 启动子表达的燕麦胚乳同源物 AsWRI1（AsWRI1）导致小麦籽粒中碳分配发生剧烈变化，种子重量降低，种子出现褶皱表型。与对照相比，AsWRI1-小麦成熟籽粒胚乳中的淀粉含量降低（按干重计从 62%降至 22%），TAG 增加了多达九倍（按干重计从 0.7%增加到 6.4%），蔗糖增加了 1.5 到 10%。AsWRI1 在小麦籽粒中的表达也导致了伸长的外周糊粉层细胞的多层化。RNA 测序、脂质分析和使用 C-蔗糖的脉冲追踪实验表明，脂肪酸的无效循环可能是油脂积累的限制因素。
我们的数据表明，燕麦胚乳 WRI1 在小麦胚乳中的表达导致了代谢的变化，这可能为生物技术应用于操纵谷物组成提供了基础。特别是，对小麦胚乳中淀粉合成的显著影响表明，WRI1 的一个重要间接作用是将碳分配从积累油脂的植物储存组织中的淀粉生物合成中转移开。
