Characterization of tobacco aquaporins: the search for CO2 pores
Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia.
Photosynthesis is a vital process that sustains nearly all life on earth and its efficiency can be limited by the diffusion of carbon dioxide (CO2) from the atmosphere to the chloroplast. A strategy to increase photosynthetic efficiency could be to facilitate the journey of CO2 to the chloroplasts by increasing mesophyll conductance. Lipid bilayers are highly permeable to CO2, however biological membranes -such as plasma membrane and chloroplast envelope- are heavily populated by proteins that reduce the area available for CO2 diffusion. Aquaporins are pore forming proteins that facilitate the transmembrane transport of not only water, but also a range of small molecules and gases. Aquaporins in the plasma membrane intrinsic proteins (PIP) sub-family have been shown to enhance permeability of the membrane to CO2, making them ideal study targets in attempts to facilitate the diffusion of CO2 to the chloroplast. Our research aims to characterize PIP aquaporins in tobacco, a model species for photosynthesis. To date one PIP gene has been described in tobacco to be a CO2 pore, NtAQP1, however beyond this there is little characterization of tobacco aquaporins in the literature. We used tomato and potato gene homologs to identify all aquaporins in the tobacco genome, resulting in the discovery of 76 aquaporin genes and 29 genes in the PIP sub-family. From these finding we will be able to identify PIPs that may facilitate CO2 diffusion across biological membranes and assess their physiological importance.