Bryden O'Gallagher MSc Candidate, Plaxton Lab, Queen's University Exploring the role of the dual-targeted 'mammalian type' purple acid phosphatase AtPAP17 in Arabidopsis thaliana phosphate and ROS metabolism
Orthophosphate (H2PO4-, Pi) is an essential, but environmentally limiting macronutrient required for many fundamental metabolic processes. Pi starved (–Pi) plants undergo a complex array of morphological and biochemical/molecular adaptations, collectively known as the ‘Pi starvation response’. Purple acid phosphatases (PAPs) play an indispensable role in the PSR by scavenging and recycling Pi from intra- and extracellular Pi-monoesters. The aim of this thesis has been to integrate biochemical and genetic approaches to help assess the role of AtPAP17 (one of 29 predicted Arabidopsis PAPs) in Pi and ROS metabolism. AtPAP17 is unique to previously characterized PAPs as it: i) is transcriptionally induced in response to Pi-starvation, leaf senescence, salinity, drought, as well as immune-related biotic stress, and ii) exists as a low molecular weight (35 kDa) ‘mammalian like’ PAP that exhibits both acid phosphatase and peroxidase activity. I determined the H2O2 peroxidase kinetics of purified AtPAP17, while demonstrating that this PAP is de novo synthesized and dual-targeted to the secretome and intracellular fraction of –Pi, senescing, or salt stressed Arabidopsis, but rapidly turned over following Pi resupply to –Pi plants. Nevertheless, loss of AtPAP17 expression in an atpap17 mutant did not influence the ability of Arabidopsis to acclimate to Pi deprivation, salinity or oxidative stress, or to recycle Pi during leaf senescence. This research field is enabling the development of innovative strategies for engineering Pi-efficient and stress-tolerant crops, urgently needed to reduce inputs of unsustainable Pi fertilizers for maximum agronomic benefit and long-term global food security and ecosystem preservation.