GA-BnaRGA-BnaLEC1分子模塊調(diào)控脂肪酸合成的通路模型

 

　　南湖新聞網(wǎng)訊 近日，華中農(nóng)業(yè)大學(xué)油菜雜種優(yōu)勢利用課題組揭示了赤霉素通過 GA-BnaRGA-BnaLEC1 信號模塊在種子發(fā)育特定階段調(diào)控甘藍型油菜種子脂肪酸生物合成中的作用，為植物激素調(diào)控脂肪酸生物合成提供了新穎的理解，同時也為高油油菜品種的選育提供了重要的理論依據(jù)。

 

　　甘藍型油菜（Brassica napus）是目前世界上主要的油料作物之一。種子含油量和脂肪酸的組分決定了菜籽的品質(zhì)和經(jīng)濟價值，提高種子含油量和改善脂肪酸組分是甘藍型油菜遺傳改良的重要目標(biāo)。多年以來，隨著油脂合成途徑的解析，人們在高油油菜品種的培育上取得了很大的突破。然而，關(guān)于植物激素信號在調(diào)節(jié)甘藍型油菜脂肪酸合成中的作用卻鮮為人知。

 

　　DELLA蛋白是赤霉素信號通路的負調(diào)控因子，在植物生長發(fā)育的多個階段均發(fā)揮著重要作用。該研究首先通過表達模式分析發(fā)現(xiàn)，甘藍型油菜DELLA蛋白家族成員BnaRGAs的表達水平在種子發(fā)育過程中被顯著抑制。進一步的研究表明，與野生型相比，BnaRGAs的兩個功能獲得型突變體bnaa6.rga-D和ds-3種子含油量顯著降低，同時脂肪酸的組分也發(fā)生變化，油酸比例降低而亞油酸比例升高。相比之下，功能缺失的四突變體bnarga在種子發(fā)育早期含油量高于對照材料，同時油酸含量增加而亞油酸含量減少。多個編碼脂肪酸合成酶基因的表達量在bnaa6.rga-D中顯著降低，表明BnaRGAs負調(diào)控甘藍型油菜脂肪酸合成。

 

　　蛋白水平的研究發(fā)現(xiàn)，BnaA6.RGA和BnaC7.RGA與種子脂肪酸合成正調(diào)控因子BnaLEC1存在蛋白互作。遺傳實驗證據(jù)表明，bnarga bnalec1六突變體種子脂肪酸組成與bnalec1雙突變體間無顯著差異，提示了BnaLEC1在脂肪酸合成中對BnaRGA存在上位性。此外，BnaA6.RGA抑制了由BnaLEC1介導(dǎo)的BnaABI3的轉(zhuǎn)錄激活，表明BnaRGA通過抑制BnaLEC1對脂肪酸合成基因的轉(zhuǎn)錄激活作用，進而抑制種子脂肪酸的合成。

 

　　該發(fā)現(xiàn)揭示了BnaRGA-BnaLEC1在種子含油量和脂肪酸的組分調(diào)控中的重要作用，為甘藍型油菜中油脂含量的提高和脂肪酸組分的調(diào)節(jié)提供了十分重要的參考依據(jù)。該研究以“DELLA Proteins BnaA6.RGA and BnaC7.RGA negatively regulate fatty acid biosynthesis by interacting with BnaLEC1s in Brassica napus” 為題發(fā)表在在Plant Biotechnology Journal上。我校植物科學(xué)技術(shù)學(xué)院博士研究生閆冠博為該論文的第一作者，馬朝芝教授和戴成副教授為論文的共同通訊作者。

 

　　【英文摘要】

 

　　Seed oil content （SOC） and fatty acid （FA） composition determine the quality and economic value of rapeseed （Brassica napus）。 Little is known about the role of gibberellic acid （GA） in regulating FA biosynthesis in B. napus. Here, we discovered that four BnaRGAs （B. napus REPRESSOR OF GA）， encoding negative regulators of GA signalling, were suppressed during seed development. Compared to the wild type, SOC was reduced in gain‐of‐function mutants bnaa6.rga‐D and ds‐3, which also showed reduced oleic acid and increased linoleic acid contents. By contrast, the loss‐of‐function quadruple mutant bnarga displayed higher SOC during early seed development than the wild type, with increased oleic acid and reduced linoleic acid contents. Notably, only BnaA6.RGA and BnaC7.RGA physically interacted with two BnaLEC1s, which function as essential transcription factors in FA biosynthesis. The FA composition did not significantly differ between bnarga bnalec1 sextuple mutants and bnalec1, suggesting that BnaLEC1s are epistatic to BnaRGAs in the regulation of FA composition. Furthermore, BnaLEC1‐induced activation of BnaABI3 expression was repressed by BnaA6.RGA, indicating that GA triggers the degradation of BnaRGAs to relieve their repression of BnaLEC1s, thus promoting the transcription of downstream genes to facilitate oil biosynthesis. Therefore, we uncovered a developmental stage‐specific role of GA in regulating oil biosynthesis via the GA‐BnaRGA‐BnaLEC1 signalling cascade, providing a novel mechanistic understanding of how phytohormones regulate FA biosynthesis in seeds. BnaRGAs represent promising targets for oil crop improvement.

 

　　論文鏈接：https://onlinelibrary.wiley.com/doi/abs/10.1111/pbi.13628