CDPKs CPK6 and CPK3 function in ABA regulation of guard cell S-type anion- and Ca(2+)-permeable channels and stomatal closure.
Abscisic acid (ABA) signal transduction has been proposed to utilize cytosolic Ca(2+) in guard cell ion channel regulation. However, genetic mutants in Ca(2+) sensors that impair guard cell or plant ion channel signaling responses have not been identified, and whether Ca(2+)-independent ABA signaling mechanisms suffice for a full response remains unclear. Calcium-dependent protein kinases (CDPKs) have been proposed to contribute to central signal transduction responses in plants. However, no Arabidopsis CDPK gene disruption mutant phenotype has been reported to date, likely due to overlapping redundancies in CDPKs. Two Arabidopsis guard cell-expressed CDPK genes, CPK3 and CPK6, showed gene disruption phenotypes. ABA and Ca(2+) activation of slow-type anion channels and, interestingly, ABA activation of plasma membrane Ca(2+)-permeable channels were impaired in independent alleles of single and double cpk3cpk6 mutant guard cells. Furthermore, ABA- and Ca(2+)-induced stomatal closing were partially impaired in these cpk3cpk6 mutant alleles. However, rapid-type anion channel current activity was not affected, consistent with the partial stomatal closing response in double mutants via a proposed branched signaling network. Imposed Ca(2+) oscillation experiments revealed that Ca(2+)-reactive stomatal closure was reduced in CDPK double mutant plants. However, long-lasting Ca(2+)-programmed stomatal closure was not impaired, providing genetic evidence for a functional separation of these two modes of Ca(2+)-induced stomatal closing. Our findings show important functions of the CPK6 and CPK3 CDPKs in guard cell ion channel regulation and provide genetic evidence for calcium sensors that transduce stomatal ABA signaling.
Mori
Izumi C
IC
Cell and Developmental Biology Section, Division of Biological Sciences and Center for Molecular Genetics, University of California San Diego, La Jolla, California, USA.
Murata
Yoshiyuki
Y
Yang
Yingzhen
Y
Munemasa
Shintaro
S
Wang
Yong-Fei
YF
Andreoli
Shannon
S
Tiriac
Hervé
H
Alonso
Jose M
JM
Harper
Jeffery F
JF
Ecker
Joseph R
JR
Kwak
June M
JM
Schroeder
Julian I
JI
D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D019441:Plant Epidermis / Q000166:cytology / Q000201:enzymology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D002118:Calcium; D015220:Calcium Channels; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D007473:Ion Channels; D011494:Protein Kinases; C516786:CPK3 protein, Arabidopsis; C516787:CPK6 protein, Arabidopsis