Lipid metabolic changes in an early divergent fungus govern the establishment of a mutualistic symbiosis with endobacteria

Abstract

The recent accumulation of newly discovered fungal-bacterial mutualisms challenges the paradigm that fungi and bacteria are natural antagonists. To understand the mechanisms that govern the establishment and maintenance over evolutionary time of mutualisms between fungi and bacteria, we studied a symbiosis of the fungus Rhizopus microsporus (Mucoromycotina) and its Burkholderia endobacteria. We found that nonhost R. microsporus, as well as other mucoralean fungi, interact antagonistically with endobacteria derived from the host and are not invaded by them. Comparison of gene expression profiles of host and nonhost fungi during interaction with endobacteria revealed dramatic changes in expression of lipid metabolic genes in the host. Analysis of the host lipidome confirmed that symbiosis establishment was accompanied by specific changes in the fungal lipid profile. Diacylglycerol kinase (DGK) activity was important for these lipid metabolic changes, as its inhibition altered the fungal lipid profile and caused a shift in the host-bacterial interaction into an antagonism. We conclude that adjustments in host lipid metabolism during symbiosis establishment, mediated by DGKs, are required for the mutualistic outcome of the Rhizopus-Burkholderia symbiosis. In addition, the neutral and phospholipid profiles of R. microsporus provide important insights into lipid metabolism in an understudied group of oleaginous Mucoromycotina. Lastly, our study revealed that the DGKs involved in the symbiosis form a previously uncharacterized clade of DGK domain proteins. mutualism evolution | antagonism | Mucoromycotina | oleaginous fungi |

Comparative genomics of Rhizophagus irregularis, R. cerebriforme, R. diaphanus and Gigaspora rosea highlights specific genetic features in Glomeromycotina

“…To assess the orthology between gene sets from the eight species of Mucoromycota sensu Spatafora et al . (), we downloaded gene models of Mortierella elongata AG‐77 v.2.0 (Uehling et al ., ), Mucor circinelloides CBS277 v.2.0 (Corrochano et al ., ), Phycomyces blakesleeanus NRRL1555 v.2.0 (Corrochano et al ., ) and Rhizopus microcarpus ATCC52814 v.1.0 (Lastovetsky et al ., ) from the JGI MycoCosm database. We clustered the predicted proteins of these taxa, together with the present Glomeromycotina predicted proteins, with FastOrtho using 50% identity and 50% coverage (Wattam et al ., ).…”

Secreted TAL effectors protect symbiotic bacteria from entrapment within fungal hyphae

“…secretion systems) to control their hosts 1 supports the hypothesis that B. rhizoxinica becomes pathogenic 'in the eyes of the fungus' if BAT proteins are absent. Indeed, multiple investigations have suggested that B. rhizoxinica endosymbionts were initially parasites before switching to mutualists 48 . For example, phylogenetic analyses indicated that B.…”

A TAL effector-like protein of symbioticMycetohabitansincreases stress tolerance and alters the transcriptome of the fungal hostRhizopus microsporus

“…The mechanism by which Btl19-13 increases the tolerance of Rhizopus to detergent is likewise unclear, but could be related to major changes in Rhizopus lipid metabolism observed during infection (Lastovetsky et al, 2016). Reprogramming of lipid metabolism in the fungus has been suggested to help meet the bacterium's nutritional requirement or favor invasion by the bacterium (Lastovetsky et al, 2016).…”

“…Bacteria were isolated from fungi by tissue disruption and filtration, and fungi were cured with antibiotics and reinfected by cocultivation, as described (Lastovetsky et al, 2016). A variety of plasmids (Table S5) with btl gene derivatives were constructed by PCR, restriction enzyme digests, and mutagenesis.…”