Expression and transport characterisation of the wheat low-affinity cation transporter (LCT1) in the methylotrophic yeast Pichia pastoris

The low-affinity cation transporter (LCT1) from wheat (Triticum aestivum) was expressed in the methylotrophic yeast Pichia pastoris and its transport characteristics studied employing Ca45 and Cd109. A clone (LCT1#3) with the highest uptake of 14 pmol of Ca/106 cells/10 min when exposed to 100 μM Ca45 was chosen for further Ca45 and Cd109 transport characteristics. We report for the first time a Km for Ca by LCT1 of 0.43 ± 0.15 mM Ca activity which confirms LCT1 to be a low affinity transporter. Interestingly, the expression of LCT1 in Pichia resulted in reduced Cd109 uptake compared to wild type cells, when cells were exposed to ⩾60 μM Cd. This is the first report of the ability of a heterologously expressed transporter to reduce the activity of endogenous transporter proteins to transport Cd. To our knowledge, this is the first demonstration of functional expression of a plant ion transporter using P. pastoris.