The Metarhizium anisopliae perilipin homolog MPL1 regulates lipid metabolism, appressorial turgor pressure, and virulence

Cells store lipids in droplets. Studies addressing how mammals controllipid-based energy homeostasis have implicated proteins of the PAT domain family, such as perilipin that surrounds the lipid droplets. Perilipin knock-out mice are lean and resistant to obesity. Factors that mediate lipid storage in fungi are still unknown. Here we describe a gene (Mpl1) in the economically important insect fungal pathogen Metarhizium anisopliae that has structural similarities to mammalian perilipins. Consistent with a role in lipid storage, Mpl1 is predominantly expressed when M. anisopliae is engaged in accumulating lipids and ectopically expressed green fluorescent protein-tagged MPL1(Metarhizium perilipin-like protein) localized to lipid droplets. Mutant M. anisopliae lacking MPL1 have thinner hyphae, fewer lipid droplets, particularly in appressoria (specialized infection structures at the end of germ tubes), and a decrease in total lipids. Mpl1 therefore acts in a perilipin-like manner suggesting an evolutionary conserved function in lipid metabolism. However, reflecting general differences between animal and fungal lineages, these proteins have also been selected to cope with different tasks. Thus, turgor generation by Delta Mpl1 appressoria is dramatically reduced indicating that lipid droplets are required for solute accumulation. This was linked with the reduced ability to breach insect cuticle so that Mpl1 is a pathogenicity determinant. Blast searches of fungal genomes revealed that perilipin homologs are found only in pezizomycotinal ascomycetes and occur as single copy genes. Expression of Mpl1 in yeast cells, a fungus that lacks a perilipin-like gene, blocked their ability to mobilize lipids during starvation conditions.