低氧调控采后苹果脂肪酸代谢途径香气形成的分子机制

Controlled atmosphere storage is one of main technologies for apple preservation, but the long-term hypoxic condition affects the biosynthesis of fruit aroma. The members of ERF VII (Ethylene response factor VII) subfamily play important roles in transcriptional regulation of hypoxic responses in plants. Our previous results indicated that hypoxic stress resulted in significant changes of the aroma components from fatty acid metabolism pathway in apple during controlled atmosphere storage. The fatty acid metabolism pathway of apple fruit might be transcriptionally regulated by MdRAP2s (RELATED TO APETALAs), the members of ERF-VII subfamily, under hypoxic condition. In the present project, ‘Golden Delicious’ apple fruit will be used as the experimental materials to investigate the effect of hypoxic stress on the aroma biosynthesis in fatty acid metabolism pathways. Yeast one-hybrid and luciferase activity assay will be applied to verify the binding of MdRAP2s on the promoters of the enzyme genes related with the biosynthesis of aroma in the fatty acid metabolism pathways. Gene silencing and over-expression technologies will be applied to testify the transcription regulation of MdRAP2s on the aroma components from fatty acid metabolism in apples. We anticipate that the project will help to decipher the underlying mechanism of how hypoxic stress affects the aroma formation of apple fruit through regulating the fatty acid metabolism, and provide the theoretical basis for maintaining and improving the flavor quality of postharvest apple fruit during controlled atmosphere storage.

气调贮藏是苹果保鲜的主要技术手段之一，但长期的低氧环境会影响果实香气的生物合成。ERF VII（Ethylene response factor VII）亚族成员在植物低氧胁迫响应过程中起到重要的转录调控作用。前期研究表明，在气调贮藏过程中，低氧胁迫造成了苹果脂肪酸代谢途径香气组分的显著变化，且该途径可能受到ERF-VII亚族成员MdRAP2s（RELATED TO APETALAs）的转录调控。本项目拟以金冠苹果为研究材料，探讨低氧胁迫对其采后脂肪酸代谢途径香气合成的影响；利用酵母单杂交和荧光素酶活性分析技术，验证MdRAP2s对脂肪酸代谢途径香气形成相关酶基因启动子的结合作用；通过基因沉默和过表达，论证MdRAP2s对低氧胁迫下苹果脂肪酸代谢途径香气形成的转录调控，以进一步阐明低氧调控苹果脂肪酸代谢途径香气形成的分子机制，为维持和改善气调贮藏过程中苹果的风味品质提供理论依据。

气调贮藏是苹果保鲜的主要技术手段之一，但长期的低氧环境会影响果实香气的生物合成。本研究以‘金冠’苹果为材料，利用气质联用、荧光定量PCR （polymerase chain reaction，聚合酶链反应）、农杆菌介导的转基因等技术，开展了低氧对果实脂肪酸代谢途径的香气生成量和合成酶基因的时空调控效应分析；明确了低氧对MdRAPs（MdERF74与MdERF75）基因的调控作用，并探讨了两基因对乙烯的响应情况；研究了乙烯响应因子MdERF74与MdERF75过表达对果实香气合成及脂肪酸含量的转录调控。主要研究结果如下：①在为期56 d贮藏过程中2 kPa O2降低了果实挥发性酯类和醇类化合物的释放，但使醛类化合物有所增加。低氧降低了贮藏期间果实乙酸丁酯、乙酸己酯、丁酸丁酯等直链酯含量，该影响可延续到货架期；而支链酯在货架期间可恢复至常氧贮藏果实的同等水平。货架期间果肉组织表现出更强的香气合成恢复能力。在56+9 d时，2 kPa O2组果肉Flesh1和Flesh2组织酯类释放量可分别恢复至Air组的48.7%和48.0%，而果皮仅为Air组的29.7%。②与较长期的低氧气调贮藏相比，短时低氧处理反而有助于提高冷藏后果实的脂氧合酶基因表达和不饱和脂肪酸的积累，进而促进其酯类香气的合成。在货架期间，短时低氧处理组果肉的乙酸己酯、乙酸丁酯、丁酸己酯、2-甲基丁酸己酯、2-甲基丁基乙酸酯的含量均显著高于低温组，这可能与短时低氧组油酸、亚油酸和亚麻酸含量的显著增加有关。③pBI121-MdERF74和pBI121-MdERF75两组过表达苹果果实的醇类和酯类含量均显著提高，但其醛类物质含量不受影响。与对照组相比，两组过表达果实中MdLOX1a和MdAAT2的表达均被上调。过表达组pBI121-MdERF74和pBI121-MdERF75果实中MdLOX1a的表达水平分别上调约0.7和1.0倍。该研究有助于进一步阐明低氧调控苹果脂肪酸代谢途径香气形成的分子机制，为维持和/或改善气调贮藏过程中苹果风味品质提供理论依据。