Distribution of DGTS in basidiomycete fungi has been
Distribution of DGTS in basidiomycete fungi has been demonstrated to be heterogeneous. In certain fungal taxons, such as Agaricales, Polyporales and Russulales, there are species that synthesize and species that do not synthesize DGTS that belong to the same order or even family (Dembitsky, 1996, Vaskovsky et al., 1998). The unstable presence of betaine Oxaliplatin in some groups of Basidiomycetes suggests a regulatory mechanism for the synthesis of DGTS in fungi. Phosphate deficiency is considered to be one a condition that triggers the synthesis of DGTS. The ability to compensate for reduced phospholipid content by producing phosphorus-free betaine lipids during Pi starvation has been shown in the photosynthetic bacteria Rhodobacter sphaeroides (Benning et al., 1995), the symbiotic soil bacteria Sinorhizobium meliloti (Geiger et al., 1999, López-Lara et al., 2003, Zavaleta-Pastor et al., 2010), the mycelial ascomycete Neurospora crassa and in the yeast K. lactis (Riekhof et al., 2014). It should be noted that several authors have suggested that there is a negative correlation between the presence and abundance of betaine lipids and PC (Eichenberger, 1982, Sato, 1992, Benning et al., 1995, Dembitsky, 1996, Vaskovsky et al., 1998). However, the mechanism behind the reciprocity between DGTS and PC remains unclear. PC biosynthesis in mushrooms has been extensively studied. In ascomycete yeasts, as in most eukaryotes, two pathways for PC synthesis have been found. One method for PC synthesis is by the methylation of phosphatidylethanolamine (PE), where PE is converted to PC by a three-step S-adenosylmethionine (AdoMet)-dependent methylation reaction. The first methylation reaction is catalyzed by the CHO2-encoded PE methyltransferase (Kodaki and Yamashita, 1987, Summers et al., 1988) and the final two methylations are catalyzed by the OPI3-encoded phospholipid methyltransferase (Kodaki and Yamashita, 1987, McGraw and Henry, 1989). When choline is present in the growth media, PC may also be synthesized by the Kennedy pathway from CDP-choline that reacts with DAG in reactions catalyzed by the CPT1-encoded choline phosphotransferase (Hjelmstad and Bell, 1987, Hjelmstad and Bell, 1990). Previous studies have suggested that the contribution of the methylation pathway for PC synthesis in Saccharomyces cerevisiae is more important but that the Kennedy pathway for PC synthesis assumes a critical role when the enzymes in the CDP-DAG pathway are defective or repressed (Carman and Henry, 1989, Greenberg and Lopes, 1996). However, it is not clear what the relative contributions of the CDP-DAG and Kennedy pathways in basidiomycetes are and whether their balance changes during adaptation to phosphate starvation. Basidiomycete xylotrophic fungus Flammulina velutipes (Curt.: Fr.) Sing. is an edible and medicinal mushroom commercially cultivated all over the world. According to the early data, fruit bodies of F. velutipes do not contain DGTS (Vaskovsky et al., 1998). In a previous report, we demonstrated that surface cultures of F. velutipes do synthesize DGTS when they are deprived of a complex of nutrients, including phosphorus, nitrogen, potassium, and some trace elements (Senik et al., 2012). The present study provides evidence that phosphorus deficiency alone induces DGTS synthesis by this fungus. This study focuses on mechanisms of reciprocity between DGTS and PC in fungi during Pi starvation. We report changes in expression of the BTA1 gene and two PC biosynthesis genes during phosphate starvation of F. velutipes culture. We describe the deduced amino acid sequence and genomic structure of the FvBTA1 gene coding for DGTS synthase in F. velutipes. We show that the FvBTA1 gene has increased transcript abundance under phosphate starvation. Despite PC depletion, expression of both PC biosynthesis genes was determined to increase. Phylogenetic relationships between putative orthologs of the BTA1 gene are also discussed.