How does the mitochondrial tail-anchored protein AtTTM1 mediate programmed cell death in plants?

Tail-anchored (TA) proteins are a class of proteins that are integrated into the membrane via their C-terminal hydrophobic sequence. TA proteins exist on all cellular membranes with diverse cellular functions, such as redox reactions, vesicular trafficking and apoptosis. They perform a variety of essential functions on the cytosolic face of cellular membranes. Due to their diverse function and unique targeting and insertion mechanisms (lack of signal peptide), TA proteins are getting significant attention in recent years. The Arabidopsis genome is believed to have over 150 TA proteins. TTM1 and 2 are TA proteins that belong to the family of Triphosphate Tunnel Metalloenzymes (TTMs). Arabidopsis, like most plants, encodes three TTM genes (AtTTM1-3). Of these, AtTTM1 and 2 are found to be mitochondrial TA proteins (Ung and Karia et al., 2017). Our recent studies revealed that both ATTM1 and 2 are involved in programmed cell death; natural aging process (senescence) and pathogen induced hypersensitive response, respectively (Ung et al., 2014, Ung and Karia et al., 2017). Based on published phospho-proteomic studies we have hypothesized that AtTTM1 is phosphorylated upon induction of the plant hormone ABA. ABA has been known to be involved in variety of stress responses and senescence. Our current data suggest that TTM1 is involved in ABA-inducible senescence through its phosphorylation by a ABA-related protein kinase. In this talk, I will discuss our current efforts to dissect the molecular mechanisms of TTM1 in aging related programmed cell death.