PhD Proposal Exam – Purva Karia (Yoshioka lab)

PhD Proposal Exam

Tuesday April 12, 10:10 am – Earth Sciences Building, Rm. ESC 3087

Purva Karia (Yoshioka lab)

“Investigation of the molecular mechanism of triphosphate tunnel metalloenzymes in Arabidopsis“

Abstract

Triphosphate tunnel metalloenzymes (TTMs) comprise a superfamily of enzymes that hydrolyze organophosphate substrates. Members of this superfamily are found across taxa, and the Arabidopsis thaliana genome encodes three TTM genes (AtTTMs). Unlike other members of this family, two of these isoforms, AtTTM1 and 2, hydrolyze pyrophosphate in vitro, making them the only TTMs characterized so far to possess pyrophosphatase activity. However, despite their high sequence identity, genetic analyses showed them to have different biological functions. AtTTM2 plays a role in pathogen resistance whereas AtTTM1 is involved in dark-induced leaf senescence. The objective for my PhD thesis project is to determine the molecular mechanism underlying the biological functions of AtTTMs. As a logical first step, I identified the involvement of AtTTM1 in natural senescence indicating that AtTTM1 plays a crucial role not only in dark-induced senescence but also in natural senescence signaling in Arabidopsis. To gain insight into their molecular mechanisms, AtTTM proteins were determined to likely localize at the mitochondrial outer membrane. Furthermore, we are exploring the connection between autophagy and AtTTM related phenotypes since autophagy is an important degradation process that regulates cell death during both senescence and pathogen resistance. More specifically, it is possible that AtTTMs are involved in mitophagy, a mitochondrial degradation process, given the subcellular localization of AtTTMs. Both transcriptional and phosphoproteomic data also suggest a connection between AtTTM1 and ABA responses. Thus, we are also investigating the connection between AtTTM1 and ABA signaling components. Finally, we are assessing whether the documented pyrophosphatase activity is required or sufficient for the in vivo function of AtTTMs. Overall, this project will provide insight into the molecular mechanisms governing AtTTMs functions and may establish novel connections between autophagy, ABA or pyrophosphatase activity and senescence and/or pathogen defense.