Mycorrhizal symbiosis between Coprinellus disseminatus and Cremastra appendiculata, insights from gene expression

Orchid seed germination is an extremely complex physiological and ecological process that includes seed development and mutualistic interactions with compatible mycorrhizal fungi. Although the mycobiont Coprinellus disseminatus associated with Cremastra appendiculata has been reported, the mutualistic interactions between them remain poorly understood. In this study, we performed physiological and transcriptomic analyses to compare symbiotic germination and ungerminated seeds of Cr. appendiculata, as well as free-living Co. disseminatus, to investigate changes in physicochemical content and identify key genes that regulate the symbiotic germination of Cr. appendiculata seeds. The results revealed the content of auxin (IAA), gibberellic acid (GA3), salicylic acid (SA) and jasmonic acid (JA) of Cr. appendiculata protocorms increased during symbiotic germination, and the content of superoxide dismutase (SOD) and catalase (CAT) in the symbiotically germinating protocorms also higher than ungerminated seeds. However, the content of peroxidases (POD) showed lower in the symbiotically germinating protocorms than ungerminated seeds. A total of 5,913 genes showing different levels of expression (log2FPKM ≥ 2.0, FDR < 0.01) in the comparison of CA and SY, and 19,077 differentially expressed genes (DEGs) genes in the comparison of CD and SY. DEGs involved in carbon metabolism, lipid metabolism, plant defense, plant hormone signal transduction and biotin metabolism were identified with significant upregulation or downregulation of genes related to metabolism observed. This work provides that mycorrhizal fungus Co. disseminatus can increase the content of endogenous hormones to promote Cr. appendiculata seed germination, and change the content of SOD, CAT to protect the plant against oxidative damage. These data may contribute to a better understanding of the molecular mechanisms of symbiotic germination and mycorrhizal fungi interactions.