Meiotic genes in the arbuscular mycorrhizal fungi: What for?

The arbuscular mycorrhizal fungi (AMF) are important symbionts of land plants, which are known for their tremendous positive effects on terrestrial ecosystems, their peculiar cellular features, and their very old evolutionary history. To date, no sexual stage or apparatus have ever been observed in these organisms; a remarkable absence for a eukaryotic lineage. For this reason, AMF have long been considered an evolutionary oddity, having evolved for over 500 millions of years in the absence of sexual reproduction and meiosis. Here, we discuss the recent identification across a number of AMF genomes, of many genes that are known to be involved in the process of meiosis in several eukaryotic model species. The presence of these genes in AMF is a previously unsuspected and highly intriguing finding, which suggests the presence of a "hidden" sexual (or parasexual) reproduction that awaits formal observation in these poorly studied fungi.