猕猴桃采后乙醛/乙醇积累的代谢调控分子生理机制研究

The acetaldehyde and ethanol are the most important volatile aroma metabolites in harvested fruits. However, they may accumulate at high levels during fruit stored at anaerobic conditions, at chilling temperature, or for long time, and then result in physiological disorder and off-flavors in fruits, which impact on the fruit flavor and quality. Kiwifruit are typical climacteric, and have presented the accumulation of acetaldehyde and ethanol during storage at room temperature, besides under controlled or modified atmosphere with low O2 or high CO2, and low temperature. The accumulation amounts of the two metabolites vary among different varieties and cultivars of kiwifruits..Kiwifruit (Actinidia chinensis var. deliciosa) cv. ‘Bruno’ accumulated at high level of acetaldehyde and ethanol, while kiwifruit (Actinidia eriantha Benth) cv. ‘White’ accumulated little of them during storage at room temperature. In order to elucidate the special mechanism on regulation of the acetaldehyde and ethanol accumulation in harvested kiwifruit, the changes in anatomical structure and gases diffusion/exchange, the key enzymes and metabolites in the pathway of respiration will be investigated between the two cultivars during storage at room temperature. Moreover, the transcriptome and proteome of ‘Bruno’ and ‘White’ fruits at pre-climacteric and post-climacteric stages will be comparatively analyzed, and the differentially expressed genes and proteins, in particularly involved in regulation of the acetaldehyde and ethanol accumulation, will be identified. Therefore, the project has an important theoretic and practical meaning, not only for controlling the accumulation of acetaldehyde and ethanol in kiwifruit during storage, but also for breeding new varieties of kiwifruit with torelance / resistance to hypoxia or anaerobic stress in harvested fruits.

乙醛和乙醇是采后果实重要的天然风味物，但乙醛、乙醇累积导致果实生理代谢紊乱，产生异味，严重影响果实风味和品质。猕猴桃是典型呼吸跃变型果实，在低氧/厌氧气调、低温胁迫、甚至在常温下后熟发生乙醛、乙醇累积，且具有基因型差异。本项目通过研究美味猕猴桃“布鲁诺”（乙醛/乙醇“积累型” ）和毛花猕猴桃“华特”果实（乙醛/乙醇“非积累型”）后熟过程中组织结构和气体交换性能的差异、呼吸代谢通路关键酶活性及代谢产物含量变化的差异，并采用RNA-Seq技术和蛋白质组学技术分析果实呼吸跃变前后基因和蛋白质的表达差异，确定与果实采后乙醛、乙醇累积相关的关键基因和特征蛋白，揭示猕猴桃果实采后乙醛/乙醇累积的内在成因、呼吸代谢通路调控的关键点和模式，并解析其调控的分子生理机制，为有效控制猕猴桃果实采后乙醛、乙醇积累提供理论依据，为选育具有良好耐/抗厌氧贮藏特性猕猴桃新品种提供借鉴。研究具有重要理论和应用价值。

乙醛和乙醇累积导致采后果实生理代谢紊乱，产生异味，严重影响果实风味和品质。本项目重点研究了美味猕猴桃‘布鲁诺’（乙醛/乙醇‘积累型’)和毛花猕猴桃‘华特’果实（乙醛/乙醇‘非积累型’) 呼吸跃变前后果实组织CO2气体交换、乙醇代谢，呼吸代谢通路的变化规律；利用RNA-seq技术分析了两种类型猕猴桃采后果实糖代谢、色素代谢、乙醇代谢、乙烯信号传导等方面基因表达的差异；研究了1-甲基环丙烯（1-MCP）处理对‘布鲁诺’果实乙醇发酵代谢和AdERF转录因子的调控。主要结果如下：.1、猕猴桃采后果实保持较高GABA代谢旁路、三羧酸循环和能量代谢活性与调控乙醇发酵代谢、抑制果实乙醇累积密切相关。.2、‘布鲁诺’与‘华特’采后果实的差异表达基因大多涉及转录、蛋白质翻译后修饰与转运、分子伴侣和信号传导机制；在这两种猕猴桃采后果实中，乙烯应答转录因子ERF和与植物色素合成相关的MYB转录因子的表达均存在显著差异。.3、通过实时荧光定量PCR验证发现，乙烯应答转录因子ERF在‘布鲁诺’和‘华特’中分别上调和下调；在丙酮酸代谢中，‘布鲁诺’果实Pyd基因大量表达，而‘华特’果实Phc基因大量表达。这些代谢通路中的关键基因差异表达导致了‘布鲁诺’和‘华特’果实采后呼吸、乙烯高峰、成熟衰老和乙醛/乙醇积累方面的差异。.4、1-MCP处理显著降低了‘布鲁诺’果实贮藏后期丙酮酸、乙醛和乙醇含量，以及乙醇发酵代谢关键酶ADH和PDC活性及其编码基因的表达，从而有效抑制了采后果实的乙醇积累。.5、1-MCP处理下调了‘布鲁诺’果实AdERF4、AdERF5、AdERF15、AdERF74和AdERF75表达，表明AdERF转录因子对1-MCP处理的响应模式存在差异，并参与调控猕猴桃采后果实的乙醇代谢。. 上述结果揭示了猕猴桃果实采后乙醛/乙醇累积的内在成因、呼吸代谢通路调控的关键点和模式，解析了猕猴桃采后果实乙醛/乙醇积累的代谢调控的分子生理机制，为有效控制猕猴桃果实采后乙醛、乙醇累积，保持果实品质提供了理论依据，也为选育具有良好耐/抗厌氧贮藏特性的猕猴桃新品种提供了技术参数。