Arabidopsis DGD1 SUPPRESSOR 1 is a Subunit of the Mitochondrial Contact Site and Cristae Organizing System and Affects Mitochondrial Biogenesis

Mitochondrial and plastid biogenesis requires biosynthesis and assembly of proteins, nucleic acids and lipids. In Arabidopsis thaliana the mitochondrial outer membrane protein DGD1 SUPPRESSOR 1 (DGS1) is part of a large multi-subunit protein complex, which contained the mitochondrial contact site and cristae organizing system (MICOS) 60 kDa subunit (MIC60), the translocase of outer mitochondrial membrane 40 kDa subunit (TOM40), the translocase of outer mitochondrial membrane 20 kDa subunits (TOM20s) and the Rieske FeS protein (RISP). A point mutation in DGS1 (dgs1-1), altered the stability and protease accessibility of this complex. This altered mitochondrial biogenesis, mitochondrial size, lipid content and composition, protein import and respiratory capacity. Whole plant physiology was affected in the dgs1-1 mutant as evidenced by tolerance to imposed drought stress and altered transcriptional responses of markers of mitochondrial retrograde signaling. Orthologs of Arabidopsis DGS1 are conserved in eukaryotes, including the NCA2 (Nuclear Control of ATP Synthase 2) protein in yeast (Saccharomyces cerevisiae), but lost in Metazoa. The genes encoding DGS1 and NCA2 are part of a similar co-expression network including genes encoding proteins involved in mitochondrial fission, morphology and lipid homeostasis. Thus, DGS1 links mitochondrial protein and lipid import with cellular lipid homeostasis and whole plant stress responses.