The methylome of the model arbuscular mycorrhizal fungus, Rhizophagus irregularis, shares characteristics with early diverging fungi and Dikarya.

Early-diverging fungi (EDF) are distinct from Dikarya and other eukaryotes, exhibiting high N6-methyldeoxyadenine (6mA) contents, rather than 5-methylcytosine (5mC). As plants transitioned to land the EDF sub-phylum, arbuscular mycorrhizal fungi (AMF; Glomeromycotina) evolved a symbiotic lifestyle with 80% of plant species worldwide. Here we show that these fungi exhibit 5mC and 6mA methylation characteristics that jointly set them apart from other fungi. The model AMF, R. irregularis, evolved very high levels of 5mC and greatly reduced levels of 6mA. However, unlike the Dikarya, 6mA in AMF occurs at symmetrical ApT motifs in genes and is associated with their transcription. 6mA is heterogeneously distributed among nuclei in these coenocytic fungi suggesting functional differences among nuclei. While far fewer genes are regulated by 6mA in the AMF genome than in EDF, most strikingly, 6mA methylation has been specifically retained in genes implicated in components of phosphate regulation; the quintessential hallmark defining this globally important symbiosis.

A putative cyclin, SiPHO80 from root endophytic fungus Serendipita indica regulates phosphate homeostasis, salinity and heavy metal toxicity tolerance.

Serendipita indica previously known as Piriformospora indica is an arbuscular mycorrhizal fungi (AMF) like endophytic fungus which can be cultivated axenically and colonizes an array of plants, thereby promoting their growth and confers biotic and abiotic stress tolerance to the colonized host plant. It efficiently sequestrates heavy metals and defends host plant against heavy metal-induced toxicity. In the present study, SiPHO80, a homologue of S. cerevisiae PHO80 was isolated from S. indica and functionally characterized in S. cerevisiae. SiPHO80 has conserved 'cyclin box' domain and closely related to negative regulator cyclin of the wood decaying fungi. In S. indica, its expression gets upregulated in phosphate-rich media. The regulation of Pi homeostasis which was disrupted in S. cerevisiae Δpho80 grown under high Pi condition was restored upon complementation with SiPHO80. Also, the expression of SiPHO80 in Δpho80 mutant restored osmotolerance and heavy metal tolerance. This is the first report of a cyclin which is involved in Pi homeostasis, salt tolerance, heavy metal toxicity tolerance in any plant growth promoting endophytic fungi.