ABSTRACT In plants, spermidine synthase (SPE) received detailed investigation due to its key roles in the biosynthesis of spermidine, a major form of polyamine. However, there is no report on the identification and characterisation of SPE in edible mushrooms. Here, a full-length cDNA of a gene encoding a potential SPE was isolated from fruiting bodies of Agaricus bisporus. Homology search, InterPro inquiry and multiple sequence alignment showed that it was a chimeric bifunctional gene (named as nSpe-Sdh) with a single transcript that could also encode saccharopine dehydrogenase (SDH). Furthermore, we found that the expression of nSPE-SDH mRNA and protein were both significantly up-regulated with the cap expansion of A. bisporus during storage. Once the protecting veil broken, both expression levels decreased to an initial storage level and remained relatively constant until the end of the storage, indicating the possible involvement of nSpe-Sdh in postharvest mushroom development. Besides, the up-regulation of the expression of nSPE-SDH mRNA and protein was both tissue-specially in cap tissues. To our knowledge, this is the first study focus on a specific gene for putative spermidine biosynthesis in edible mushrooms. Our present study provides valuable information for further functional characterisation of SPE-SDH proteins in postharvest mushroom physiology.

中文翻译：

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新型嵌合亚精胺合酶-糖碱脱氢酶基因可能在蘑菇（双孢蘑菇）采后发育中发挥作用

摘要 在植物中，亚精胺合酶 (SPE) 因其在亚精胺（多胺的主要形式）的生物合成中的关键作用而受到详细研究。但目前尚无关于食用菌中SPE的鉴定和表征的报道。在这里，从双孢蘑菇子实体中分离出编码潜在 SPE 的基因的全长 cDNA。同源性搜索、InterPro 查询和多序列比对表明，它是一个嵌合双功能基因（命名为 nSpe-Sdh），具有单个转录本，也可以编码糖碱脱氢酶（SDH）。此外，我们发现 nSPE-SDH mRNA 和蛋白质的表达都随着双孢蘑菇在储存过程中的帽扩张而显着上调。一旦防护罩破裂，两种表达水平均降至初始储存水平，并在储存结束前保持相对稳定，表明 nSpe-Sdh 可能参与采后蘑菇发育。此外，nSPE-SDH mRNA和蛋白质表达的上调都是组织的，特别是在帽组织中。据我们所知，这是第一项针对可食用蘑菇中假定亚精胺生物合成的特定基因的研究。我们目前的研究为采后蘑菇生理学中 SPE-SDH 蛋白的进一步功能表征提供了有价值的信息。据我们所知，这是第一项针对可食用蘑菇中假定亚精胺生物合成的特定基因的研究。我们目前的研究为采后蘑菇生理学中 SPE-SDH 蛋白的进一步功能表征提供了有价值的信息。据我们所知，这是第一项针对可食用蘑菇中假定亚精胺生物合成的特定基因的研究。我们目前的研究为采后蘑菇生理学中 SPE-SDH 蛋白的进一步功能表征提供了有价值的信息。