Understanding aquaporins as potential enhancers of photosynthesis and plant performance

Groszmann M, De Rosa A, Mani-George A, Skinner S, von Caemmerer S and Evans JR

ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra ACT, 2601.

Plants are in constant exchange with the surrounding environment, absorbing and transporting nutrients and gases essential for growth. Aquaporins represent a major class of channel proteins that aid in this process by increasing the permeability of biological membranes. Different aquaporin isoforms can selectively facilitate the transmembrane transport of not only water, but also a range of other small molecules and gases necessary for optimal plant performance. Amongst these is carbon dioxide (CO2), a key substrate for photosynthesis. For the majority of plants, photosynthetic efficiency is limited by the amount of CO2 diffusion from the atmosphere to the chloroplast where it is fixed into sugars. A strategy to increase photosynthetic efficiency could be to use aquaporins to enhance CO2 diffusion to the chloroplasts by increasing transport across the plasma membrane and chloroplast envelope (collectively termed mesophyll conductance). Of the few aquaporins so far shown to enhance membrane permeability to CO2, these all belong to the Plasma membrane Intrinsic Proteins (PIP) sub-family. PIP aquaporins also transport a range of other substrates necessary for optimal plant performance, making them exciting targets for engineering crop improvements. I will present our progress towards characterising PIP aquaporin biology and their potential translational use in crop species.