油酸脱氢酶基因fad2突变协同调控花生高油酸和低棕榈酸的分子机制

Increasing oleic acid and decreasing palmitic acid content have enhanced the nutritive value and storage quality of peanut (Arachis hypogaea L.), so it has been to an important objective for peanut quality improvement. The high oleate peanut line F435 with 80% oleic acid and 2% linoleic acid possesses only 6% of palmitic acid content, which is nearly half of the normal peanut (12%). Previous studies had confirmed that the molecular mechanism of high oleic acid character was caused by mutation of the two oleoyl-PC desaturase encoded by fad2 genes, but the mechanism of the fad2 mutation affecting the reduction of palmitic acid content is still unknown. Near isogenic lines (NILs) of high oleic acid/low palmitic acid (genotype ol1ol1ol2ol2) and normal oleic/normal palmitic acid (genotype OL1OL1OL2OL2) were developed to study the synergetic modulation mechanism. In this project, developing seeds of the NILs will be analyzed by RNA-Sequencing and transcriptome profiling to identify candidate genes. Genes with transcriptional difference and involved in fatty acid biosynthesis pathway will be selected, and the expressing level of them in seed at different developing stages will be detected by Real-time PCR. Meanwhile, the fatty acid composition, lipid structure of TAG, DAG, PC as well as the size and composition of acyl-CoA pools of seeds from NIL will also be analyzed. In the end, all the results will be integrated to reveal the mechanisms for the fad2 mutation affecting the decrease of palmitic acid content. The implementation of this project will provide theory for enhancement of peanut quality.

提高油酸和降低棕榈酸有益于花生营养保健价值及加工贮藏特性的改善，是花生品质改良研究的重要方向。与普通油酸花生相比，高油酸花生突变体F435的油酸显著提高（从50%提高到80%），亚油酸显著降低（从35%下降到2%），同时棕榈酸也从12%下降到6%，高油酸花生油的品质得到显著提升。前人研究证实F435高油酸形成的分子机制是两个油酸脱氢酶基因fad2发生隐性突变所致，但这一突变如何同时导致棕榈酸含量的显著下降，目前尚未见研究报道。本项目以构建的花生高油酸（低棕榈酸）和普通油酸（普通棕榈酸）近等基因系为材料，研究两者在种子脂肪酸快速积累期的转录组和脂质合成关键基因的表达差异，结合种子脂肪酸组分、酯酰-CoA、DAG和PC含量以及脂质结构差异分析，从基因表达水平差异和脂质合成中间产物含量变化两个方面，解析fad2协同调控花生高油酸和低棕榈酸的分子机制，为花生脂肪酸遗传改良提供理论和技术支撑。

脂肪酸组成是影响花生籽仁品质的重要因素，已有研究表明AhFad2基因突变能同时提高油酸和降低棕榈酸含量，有益于花生营养保健价值及加工贮藏特性的改善，明确AhFad2基因突变协同调控花生高油酸和低棕榈酸的分子机制，将为解析花生不同脂肪酸含量的精准调控提供理论和技术支撑。为此，本研究以花生高油酸（低棕榈酸）和普通油酸（普通棕榈酸）近等基因系为材料，研究两者在种子脂肪酸快速积累期的转录组和脂质合成关键基因的表达差异，结合种子脂肪酸组分、酯酰-CoA、DAG和PC含量以及脂质结构差异分析，从基因表达水平差异和脂质合成中间产物含量变化两个维度，解析AhFad2协同调控花生高油酸和低棕榈酸的分子机制。研究结果表明：编码硬脂酰ACP去饱和酶FAB2的基因Aradu.RI4NB和Araip.XM2MR在ZH16-HO中的表达量显著高于ZH16-NO中的表达量，这个酶主要作用于硬脂酸脱氢生成油酸，高油酸材料中这两个基因的表达量显著提高对棕榈酰-ACP的流向进行了重新分配，使得更多的棕榈酰-ACP流向去饱和途径进而生成油酸，从而减少了流向硫酯酶水解生成棕榈酸的途径，最终造成了棕榈酸含量的下降和油酸含量的提高，这一协同调控的“一因多效”机制也在本研究中开展的油酸和棕榈酸含量QTL定位研究中得到证实，即本研究中发现棕榈酸和油酸的主效QTL在遗传图谱上共定位，并与AhFad2基因在物理图谱上重叠。另外，本研究还解析了AhFad2基因家族对种子低温萌发的反应，同时也建立了油酸、棕榈酸等主要脂肪酸含量的近红外检测模型，培育出高油酸、低棕榈酸花生新品种并成功实现成果转化。