茶树中存在2个亚细胞定位不同的NUDX1基因（CsNUDX1-cyto和CsNUDX1-chlo）,其中定位于细胞质的CsNUDX1-cyto基因与香叶醇生物合成密切相关。为探究NUDX1基因在不同茶树品种中的序列、功能差异及其在物种间的进化,通过序列比对、基因克隆、进化树构建、代谢物分析、功能验证等分析了该基因在茶树与非茶树植物中的进化以及香叶醇积累差异。结果表明,不同茶树基因库中组装的CsNUDX1s核苷酸序列存在差异;RT-PCR克隆显示4个阿萨姆变种和4个中国变种茶树中均有CsNUDX1-cyto和CsNUDX1-chlo的阳性克隆,且核苷酸序列存在差异。利用Phytozome网站数据进行序列比对及进化树构建,结果显示共有58个植物中存在CsNUDX1同源基因;该基因在植物物种间较为保守,在低等植物藻类基因组中也存在;在单子叶禾本科植物中,除短柄草（Brachypodium distachyon）泛基因组中存在蛋白序列匹配率大于58%的目的基因,其余均较低,尤其是在部分禾本科植物中该基因存在缺失。代谢物分析表明15个禾本科植物水稻、小麦和玉米品种鲜叶中均未检测到香叶醇的合成,而4个茶树品种嫩梢中香叶醇含量为0.87~4.12 μg·g-1。此外,茶树CsNUDX1s基因在幼嫩叶片中有高表达;阿萨姆变种茶树佛香3号的CsNUDX1-cyto同样具有合成香叶醇的功能。本研究表明,NUDX1基因广泛存在植物基因组中,在茶树基因组中存在2个CsNUDX1s基因,并与茶树叶片中香叶醇的合成相关。
Geraniol is an acyclic monoterpene alcohol, which plays key roles in plant-environment interactions, such as pest repelling, antimicrobial activity, and pollinator attraction as well as the aroma traits for tea plants. It was reported that a cytosolic Nudix hydrolase (NUDX1) catalyzes geranyl pyrophosphate (GPP) into geranyl monophosphate (GP), followed by dephosphorylation with an endogenous phosphatase to produce geraniol. Two homologues of AtNUDX1 were found in tea genome (CsNUDX1-cyto and CsNUDX1-chlo) with different subcellular location. Searching the homologues of AtNUDX1 on Phytozome shows that fifty-eight plant species contain the homologues of AtNUDX1 (with identities>64%). However, no homologue of AtNUDX1 was found in the genomes of grass species, with the exception of Brachypodium distachyon. We thus detected AR2000-enzymed geraniol in fresh leaves of rice, wheat, maize, and tea plants. The results show that free geraniol was undetectable in fresh leaves of rice, wheat and maize, where as young shoots of four tea cultivars had high levels of geraniol (0.87-4.12 μg·g-1). Two CsNUDX1 genes were highly expressed in young tea leaves and had a positive correlation (above 0.7) with the accumulation of geraniol. This study shows that NUDX1s are widely present in plant genome, which are closely related to the formation of geraniol.
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