Functional Analysis of the Promoter for Phytoalexin Synthesis Gene

马铃薯晚疫病病菌疫霉（Phytophthora infestans）的不亲和性小种对马铃薯块茎组织产生多重防御反应，包括氧化爆发、倍半萜类植物抗毒素（lubimin和vishitin）的积累。在马铃薯块茎中，用真菌菌丝体的粗激发剂（菌丝壁成分；HWC）处理也能诱导所有这些反应。倍半萜环化酶是类异戊二烯途径中合成倍半萜植物抗毒素的关键酶。该基因在植物与病原体相互作用中的表达还没有很好的文献记载。本研究分离并鉴定了马铃薯倍半萜环化酶、猪螺旋体二烯合成酶（PVS）的CDNA编码。PVS由多基因家族（PVS1-PVS4）编码。作为一种阐明马铃薯块茎植物抗毒素合成调控机制的分子方法，我们研究了PVS转录物水平随时间的变化。这些成员分别受到不相容和相容的病原菌种族的刺激。有趣的是，只有PVS3在马铃薯叶片中被诱导。我们从马铃薯基因组文库中分离并鉴定了PVS3基因。荧光素酶（Luc）报告基因在PVS3启动子控制下的瞬时表达表明，真菌激发子诱导了高水平的Luc活性。这些结果表明，启动子区域含有防御反应的顺式作用元件。

Exposure of potato tuber tissues to incompatible race of Phytophthora infestans, a pathogen of potato late blight, causes multiple defense responses, including the oxidative burst, accumulation of sesquiterpenoid phytoalexins (lubimin and rishitin). All these reactions are also induced in potato tubers by the treatment with a crude elicitor preparation (hyphal wall component ; HWC) from the mycelium of the fungus. Sesquiterpene cyclase is a key enzyme in isoprenoid pathway for the synthesis of sesquiterpenoid phytoalexin. The expression of the gene in plant-pathogen interactions is not well documented. Here we isolated and characterized CDNA encoding potato sesquiterpene cyclase, vetispiradiene synthase (PVS). PVS was encoded by multiple gene family (PVS1-PVS4). As one molecular approach to elucidation of the mechanisms that regulate the phytoalexin synthesis in potato tubers, we investigated changes with time in the transcript levels of PVS. These members were stimulated by an incompatible and a compatible races of P. infestans. Interestingly, only PVS3 was induced in the potato leaves.We isolated and characterized the PVS3 genes from a potato genomic library.Transient expression of luciferase (Luc) reporter gene under the control of PVS3 promoter showed that high level of Luc activity was induced by the fungal elicitor. These results indicated that the promoter region contains cis-acting element for defense response.