Diphosphomevalonate decarboxylase; part of the second module of ergosterol biosynthesis pathway that includes the middle steps of the pathway (By similarity). The second module involves the formation of farnesyl diphosphate, which is also an important intermediate in the biosynthesis of ubiquinone, dolichol, heme and prenylated proteins (By similarity). This module also plays a key role in the biosynthesis of triterpenes such as ganoderic acids (GA), a group of highly oxygenated lanostane-type triterpenoids which are well recognized as a main group of unique bioactive compounds in the medicinal mushroom Ganoderma lucidum (PubMed:22203490, PubMed:29476632). Activity by the mevalonate kinase first converts mevalonate into 5-phosphomevalonate (By similarity). 5-phosphomevalonate is then further converted to 5-diphosphomevalonate by the phosphomevalonate kinase (By similarity). The diphosphomevalonate decarboxylase MVD then produces isopentenyl diphosphate (PubMed:22203490). The isopentenyl-diphosphate delta-isomerase then catalyzes the 1,3-allylic rearrangement of the homoallylic substrate isopentenyl (IPP) to its highly electrophilic allylic isomer, dimethylallyl diphosphate (DMAPP) (By similarity). Finally the farnesyl diphosphate synthase FPS catalyzes the sequential condensation of isopentenyl pyrophosphate with dimethylallyl pyrophosphate, and then with the resultant geranylpyrophosphate to the ultimate product farnesyl pyrophosphate (PubMed:18540102). (R)-5-diphosphomevalonate + ATP = ADP + CO2 + isopentenyl diphosphate + phosphate Isoprenoid biosynthesis; isopentenyl diphosphate biosynthesis via mevalonate pathway; isopentenyl diphosphate from (R)-mevalonate: step 3/3. Expression levels are relatively low in the mycelium. 53.9-fold higher expression level in the primordia than in the 20-day old mycelia. By methyl jasmonate (MeJA). Belongs to the diphosphomevalonate decarboxylase family.