Calmodulin-binding proteins in bryophytes: identification of abscisic acid-, cold-, and osmotic stress-induced genes encoding novel membrane-bound transporter-like proteins.
Plant responses to environmental stresses are mediated in part by signaling processes involving cytosolic Ca2+ and a Ca(2+)-binding protein, calmodulin. Screening with radiolabeled calmodulin of a cDNA library of the moss Physcomitrella patens resulted in identification of genes encoding novel membrane transporter-like proteins, MCamb1 and MCamb2. These proteins each had a central hydrophobic domain with two putative membrane spans and N- and C-terminal hydrophilic domains, and showed sequence similarity to mammalian inward rectifier potassium channels. Calmodulin binds to MCamb1 and MCamb2 via interaction with basic amphiphilic amino acids in the C-terminal domain. Levels of MCamb1 and MCamb2 transcripts increased dramatically following treatment with low temperature, hyperosmotic solutes, and the stress hormone abscisic acid, all of which were previously shown to increase cellular tolerance to freezing stress. These results suggest that calmodulin participates in cellular signaling events leading to enhancement of stress resistance through regulation of novel transporter-like proteins.
Takezawa
Daisuke
D
Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo 060-0819, Japan. daisuket@pop.lowtem.hokudai.ac.jp
Minami
Anzu
A
D000040:Abscisic Acid / Q000494:pharmacology*; D000595:Amino Acid Sequence; D044002:Bryophyta / Q000187:drug effects / Q000378:metabolism; D019068:Bryopsida / Q000187:drug effects / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000737:chemistry* / Q000145:classification / Q000302:isolation & purification / Q000378:metabolism*; D002478:Cells, Cultured; D003080:Cold Temperature; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008969:Molecular Sequence Data; D009997:Osmotic Pressure; D015221:Potassium Channels / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D014882:Water-Electrolyte Balance / Q000502:physiology*
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D007473:Ion Channels; D015221:Potassium Channels; D000040:Abscisic Acid