An evolutionarily conserved phosphatidate phosphatase maintains lipid droplet number and ER morphology but not nuclear morphology

Abstract

Phosphatidic acid phosphatases are involved in the biosynthesis of phospholipids and triacylglycerol, and also act as transcriptional regulators. Studies to ascertain its role in lipid metabolism and membrane biogenesis are restricted only to Opisthokonta and Archaeplastida. Herein, we report the role of phosphatidate phosphatase (PAH) in Tetrahymena thermophila, belonging to the Alveolata clade. We identified two PAH homologs in Tetrahymena, TtPAH1, and TtPAH2. Loss of function of TtPAH1 results in reduced lipid droplet number and increase in ER content. It also shows more ER sheet structure as compared to wild type Tetrahymena. Surprisingly, we did not observe a visible defect in nuclear morphology of ΔTtpah1 mutant. TtPAH1 rescued all the known defects in yeast pah1Δ strain and is conserved functionally between Tetrahymena and yeast. The homologous gene derived from Trypanosoma also rescued the defects of yeast pah1Δ strain. Our results indicate that PAH, previously known to be conserved between Opisthokonts, is also present in a set of distant lineages. Thus, a phosphatase cascade is evolutionarily conserved and is functionally interchangeable across eukaryotic lineages.