Maize PIMT2 repairs the damaged 3-METHYLCROTONYL COA CARBOXYLASE in mitochondria controlling seed vigor.

PROTEIN L-ISOASPARTYL O-METHYLTRANSFERASE (PIMT) regulates seed vigor by repairing damaged proteins. While capable of isoaspartyl repair in all proteins, those proteins most susceptible to isoAsp formation have not been well characterized and the mechanisms of PIMT regulation of seed vigor remains largely unknown. Using Co-IP and LC-MS/MS, maize (Zea mays) PIMT2 (ZmPIMT2) interacted predominantly with both subunits of maize 3-METHYLCROTONYL COA CARBOXYLASE (ZmMCC). ZmPIMT2 is specifically expressed in maize embryo. Both mRNA and protein accumulation of ZmPIMT2 increased during seed maturation and declined during imbibition. Maize seed vigor was decreased in the zmpimt2 mutant line while overexpression of ZmPIMT2 in maize and Arabidopsis thaliana increased seed vigor upon artificial aging. ZmPIMT2 was localized in the mitochondria, as determined by subcellular localization assays in maize protoplast. ZmPIMT2 binding to ZmMCCα was confirmed by luciferase complementation tests in both tobacco (Nicotiana benthamiana) leaves and maize protoplasts. Knock down of ZmMCCα decreased maize seed aging tolerance. Furthermore, overexpression of ZmPIMT2 decreased the accumulation of isoAsp of ZmMCCα protein in seed embryos that were treated with accelerated aging. Taken together, our results demonstrated that ZmPIMT2 binds ZmMCCα in mitochondria, repairing isoAsp damage, and positively regulates maize seed vigor.