A Putative Two Pore Channel AtTPC1 Mediates Ca2+ Flux in Arabidopsis Leaf Cells

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Abstract
The gene encoding voltage-gated channel with high affinity for Ca2+ permeation has not been cloned from plants. In the present study, we isolated a full-length cDNA encoding a putative Ca2+ channel (AtTPC1) from Arabidopsis. AtTPC1 has two conserved homologous domains, both of which contain six transmembrane segments (S1–S6) and a pore loop (P) between S5 and S6 in each domain, and has the highest homology with the two pore channel TPC1 recently cloned from rat. The overall structure is similar to the half of the general structure of α-subunits of voltage-activated Ca2+ channels from animals. AtTPC1 rescued the Ca2+ uptake activity of a yeast mutant cch1. Sucrose-induced luminescence, which reflects a cytosolic free Ca2+ increase in aequorin-expressing Arabidopsis leaves, was enhanced by overexpression of AtTPC1 and suppressed by antisense expression of it. Sucrose-H+ symporters AtSUC1 and 2, which depolarize membrane potential of cells receiving sucrose, also depressed a Ca2+ increase by their antisense expression. These results suggest that AtTPC1 mediates a voltage-activated Ca2+ influx in Arabidopsis leaf cells.