Novel Chimeric Spermidine Synthase-Saccharopine Dehydrogenase Gene With A Possible Role In Postharvest Development Of The Button Mushroom (Agaricus Bisporus)

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.