Spermidine Synthase and Saccharopine Reductase Have Co-Expression Patterns Both in Basidiomycetes with Fusion Form and Ascomycetes with Separate Form

Gene fusion is a process through which two or more distinct genes are fused into a single chimeric gene. Unlike most harmful fusion genes in cancer cells, in this study, we first found that spermidine synthetase- (SPDS, catalyst of spermidine biosynthesis) and saccharopine reductase- (SR, catalyst of the penultimate step of lysine biosynthesis) encoding genes form a natural chimeric gene, , in . Through the cloning of full-length ORFs in different strains and the analysis of alternative splicing in developmental stages, has only one copy and unique transcript encoding chimeric SPDS-SR in . By an orthologous gene search of in more than 80 fungi, we found that the chimeric exists in basidiomycetes, while the two separate and independently exist in ascomycetes, chytridiomycetes, and oomycetes. Further, the transcript level of was investigated in different developmental stages and under some common environmental factors and stresses by RT-qPCR. The results showed that mainly up-regulated in the elongation stage and pileus development of , as well as under blue light, high temperature, HO, and MeJA treatments. Moreover, a total of 15 sets of RNA-Seq data, including 218 samples of , were downloaded from the GEO database and used to analyze the expression correlation of and . The results showed that the separate and shared highly similar co-expression patterns in the samples with different strains and different nutritional and environmental condition treatments. The chimeric in basidiomycetes and the co-expression pattern of the and in indicate the special link of spermidine and lysine in fungi, which may play an important role in the growth and development of fruiting body and in response to the multiple environmental factors and abiotic stresses.