Terrestrial plants lack inositol-1,4,5-trisphosphate (IP3) receptor regulating transient Ca2+ increase to activate cellular Ca2+-dependent physiological events. To understand an evolutional route of the loss of the IP3 receptor gene, conservation of the IP3 receptor gene in algae was examined in silico based on the accumulating information of genomes and expression sequence tags. Results clearly demonstrated that the lack of the gene was observed in Rhodophyta, Chlorophyta except for Volvocales and Streptophyta. It was therefore hypothesized that the plant IP3 receptor gene was eliminated from the genome at multiple occasions; after divergence of Chlorophyta and Rhodophyta and of Chlorophyta and Charophyta.
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