Researchers at the University of Adelaide have discovered that a protein which mediates the transport of alkali metal ions, such as potassium, and halides ions across plant membranes acts similarly to a protein found in animals.
Grapevine CCC protein (in two nearly orthogonal orientations) transports potassium (purple) and chloride (green) ions through the pore (black dots) in an electroneutral fashion. Credit: Maria Hrmova.
The protein is a cation-chloride cotransporter (CCC), and these are present in all cellular life forms. Some CCCs are able to transport two types of ions, both potassium and halide chloride, while others can also transport a third - sodium.
The selectivity of plant CCCs has been controversial, and it was previously understood that they are sodium-potassium-chloride symporters. However, University of Adelaide researchers found that a range of plants, such as grapevine, tobacco, rice, pumpkin, barrel clove, and green algae have two-ion CCCs, similar to those which are found in animals.
"We showed that the structural signatures of ion binding sites in grapevine CCC resemble those of animal potassium-chloride symporters," said Professor Maria Hrmova, who previously worked on plant transport proteins.
"Our findings widen the role of plant CCC proteins in plant biology and will have implications for the bioengineering of plants for food production and plant survival. This will be the subject of future studies.
"Understanding the properties of these transporters at the molecular level is important for bioengineering to design novel proteins with improved characteristics, such as permeation selectivity, thermostability, and folding."
The findings were published in the International Journal of Molecular Sciences, a forum for fundamental research at the intersection of biochemistry, biophysics and biology. It was also selected as a feature paper in molecular plant sciences.
The research, which made use of large-scale bioinformatics with ancestral sequence reconstruction, 3D protein modelling, and transport thermodynamics, will allow plant breeders to understand how this protein works and to develop higher quality and more nutritious crops.
"This new concept of grapevine CCC properties is fundamental to the survival of plants as they mediate ion uptake, govern the distribution of solutes through plants, remove toxins from the cytosol, and recycle valuable molecules," said Professor Hrmova.
"Given their specific gatekeeping functions, membrane transporters are attractive targets in agricultural biotechnology for increasing nutrient contents in edible parts of crop plants, and excluding toxic elements, both which directly relate to crop quality and ultimately sustained food production."
