Functional Analysis of a Rice Putative Voltage-Dependent Ca2+ Channel, OsTPC1, Expressed in Yeast Cells Lacking its Homologous Gene CCH1

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Abstract
We isolated a cDNA (OsTPC1) from rice that was homologous to AtTPC1, a putative voltage-dependent Ca2+ channel (VDCC) gene of Arabidopsis thaliana. The hydropathy profile of its deduced amino acid sequence showed significant structural features of the α1-subunit of animal VDCCs. Functional analysis using a heterologous yeast expression system showed that OsTPC1 facilitates Ca2+ permeation. The Km value for Ca2+ of OsTPC1, 47.5 µM, was comparable to that of intrinsic CCH1, a candidate VDCC in yeast. Ca2+ permeation by OsTPC1 was inhibited by verapamil, a VDCC blocker. These findings indicate for the first time that OsTPC1 is a putative VDCC in rice.