Tobacco aquaporin NtAQP1 and human aquaporin hAQP1 contribute to single cell photosynthesis in Synechococcus

Abstract

Background information: Aquaporins are H₂O-permeable membrane protein pores. However, some aquaporins are also permeable to other substances such as CO₂. In higher plants, overexpression of such aquaporins has already led to an enhanced photosynthetic performance due to improved CO₂ mesophyll conductance. In this work, we investigated the effects of such aquaporins on unicellular photosynthetically active organisms, specifically cyanobacteria.

Results: Overexpression of aquaporins NtAQP1 or hAQP1 that might have a function to improve CO₂ membrane permeability lead to increased photosynthesis rates in the cyanobacterium Synechococcus sp. PCC7002 as concluded by the rate of evolved O₂. A shift in the Plastoquinone pool state of the cells supports our findings. Water permeable aquaporins without CO₂ permeability, such as NtPIP2;1, do not have this effect.

Conclusions and significance: We conclude that also in single cell organisms like cyanobacteria, membrane CO₂ conductivity could be rate limiting and CO₂-porins reduce the respective membrane resistance. We could show that besides the tobacco aquaporin NtAQP1 also the human hAQP1 most likely functions as CO₂ diffusion facilitator in the photosynthesis assay.

Keywords: CO2 membrane permeability; Synechococcus sp. PCC 7002; aquaporins; cyanobacteria; photosynthesis.