肌醇半乳糖苷合成酶基因调节甜瓜光合产物韧皮部装载和运输的机制研究

Melon (Cucumis melo L.) belongs to a group of plants that mainly transport raffinose family oligosaccharides (RFOs). These plants were called RFO transporting species with a phloem loading mechanism known as "polymer trapping". Galactinol synthase (GAS) is the key enzyme of RFO synthesis. It has been hypothesized that GAS plays a key role in phloem loading and transport of photoassismilates in melon and enhancing the expression of GAS is expected to increase phloem loading and transport of photoassimilates and consequently improve melon plant growth and yield formation. Two genes CmGAS1 and CmGAS2 have been cloned from melon and they are specifically expressed in the minor veins of source leaves. The promoter of CmGAS1 has also been cloned. The objective of the proposed work is to overexpress CmGAS1 and CmGAS2 in melon using the native promoter of CmGAS1 to gain a better understanding of the role of GAS in phloem loading and transport of RFOs in melon. This will represent a new approach for breeding melon genotypes of high yield and quality via enhancing the expression of GAS in melon and other cucurbits.

甜瓜 (Cucumis melo L.) 是棉子糖系列寡糖 (RFOs) 转运型植物的典型代表，韧皮部装载策略采用 "聚合物陷阱" 机制。肌醇半乳糖苷合成酶 (GAS) 是催化 RFOs 合成的关键酶。提高 GAS 基因的表达很可能会增强源叶碳水化合物韧皮部装载和外运速率，从而达到从根本上调控果实产量与品质形成的目标。两个 GAS 基因 CmGAS1、CmGAS2 已经从甜瓜中克隆并在叶片的小叶脉中特异表达，CmGAS1 基因启动子也已经被克隆。本研究拟从分析源库变化对 GAS 基因表达的影响入手,应用 CmGAS1 基因特异性启动子构建 CmGAS1 和 CmGAS2 的过表达载体并进行甜瓜遗传转化，进而明确 GAS 基因对甜瓜光合同化产物韧皮部装载和运输的调节机制。探索通过提高 GAS 基因的表达来增强甜瓜叶片中碳水化合物的外运从而提高其产量和品质，为葫芦科作物遗传育种研究提供新思路。

项目背景：光合同化产物是果实产量与品质形成的基础。甜瓜果实中糖的含量和种类是衡量甜瓜果实品质的重要指标。甜瓜是棉子糖系列寡糖 (RFOs) 转运型植物的典型代表，甜瓜韧皮部装载策略采用 “聚合物陷阱” 机制。肌醇半乳糖苷合成酶 (GAS) 是催化 RFOs 合成的关键酶，提高 GAS 基因的表达很可能会增强源叶碳水化合物韧皮部装载和外运速率，从而达到从根本上调控果实产量与品质形成的目标。主要研究内容：本研究应用 CmGAS 基因特异性启动子构建 CmGAS 的过表达载体并进行甜瓜遗传转化，对转基因植株进行分子检测及生理检测，明确 GAS 基因在甜瓜光合同化产物韧皮部装载和运输方面的生理功能。重要结果及关键数据：对转基因植株进行 PCR 检测，获得 8 株阳性转基因植株，并对转基因植株进行田间生理指标的鉴定。结果表明：转基因植株与对照相比，叶片的净光合速率、气孔导度、胞间CO2 浓度、蒸腾速率均有显著提高；甜瓜果实的单瓜重、纵径、横径、果肉厚度均有所增加；叶片中的葡萄糖、蔗糖、棉子糖和水苏糖含量平均增加了4.37%，23.32%，12.78% 和 37.36%。果实中未能检测到水苏糖，转基因植株果实中的葡萄糖、果糖、蔗糖以及棉子糖含量均有所提高。科学意义：提高甜瓜 GAS 基因的表达可以显著提高甜瓜叶片碳水化合物的合成从而达到提高甜瓜果实品质和产量的目标，并获得甜瓜转 GAS 基因新种质，这为葫芦科作物遗传育种研究提供了新思路。