MAP kinases MPK9 and MPK12 are preferentially expressed in guard cells and positively regulate ROS-mediated ABA signaling.
by Jammes F., Song C., Shin D., Munemasa S., Takeda K., Gu D., Choa D., Lee S., Giordo R., Sritubtim S., Leonhardt N., Ellis B. E., Murata Y., Kwak J. M. (2009)
- Fabien Jammesa,1,
- Charlotte Songa,1,2,
- Dongjin Shina,1,3,
- Shintaro Munemasab,
- Kouji Takedaa,
- Dan Gua,
- Daeshik Choa,
- Sangmee Leea,
- Roberta Giordoa,c,
- Somrudee Sritubtimd,4,
- Nathalie Leonhardte,
- Brian E. Ellisd,
- Yoshiyuki Muratab and
- June M. Kwaka,5
aDepartment of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742;
bGraduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan;
cDepartment of Botany and Plant Ecology, University of Sassari, 07100 Sassari, Italy;
dMichael Smith Laboratories, University of British Columbia, Vancouver, BC, Canada V6T 1Z4; and
eLaboratoire des Echanges Membranaires et Signalisation, Unité Mixte de Recherche 6191, Centre National de la Recherche Scientifique-Commissariat à l’Energie Atomique-Université Aix-Marseille II, Commissariat à l’Energie Atomique Cadarache Bat 156, 13108 St Paul-lez-Durance, France
in Proc. Natl. Acad. Sci. U.S.A. 106, 20520–20525. doi: 10.1073/pnas.0907205106 –
PubMed Abstract | CrossRef Full Text | Google Scholar
Reactive oxygen species (ROS) mediate abscisic acid (ABA) signaling in guard cells. To dissect guard cell ABA-ROS signaling genetically, a cell type-specific functional genomics approach was used to identify 2 MAPK genes, MPK9 and MPK12, which are preferentially and highly expressed in guard cells.
To provide genetic evidence for their function, Arabidopsis single and double TILLING mutants that carry deleterious point mutations in these genes were isolated. RNAi-based gene-silencing plant lines, in which both genes are silenced simultaneously, were generated also. Mutants carrying a mutation in only 1 of these genes did not show any altered phenotype, indicating functional redundancy in these genes.
ABA-induced stomatal closure was strongly impaired in 2 independent RNAi lines in which both MPK9 and MPK12 transcripts were significantly silenced. Consistent with this result, mpk9-1/12-1 double mutants showed an enhanced transpirational water loss and ABA- and H2O2-insensitive stomatal response.
Furthermore, ABA and calcium failed to activate anion channels in guard cells of mpk9-1/12-1, indicating that these 2 MPKs act upstream of anion channels in guard cell ABA signaling.
An MPK12-YFP fusion construct rescued the ABA-insensitive stomatal response phenotype of mpk9-1/12-1, demonstrating that the phenotype was caused by the mutations. The MPK12 protein is localized in the cytosol and the nucleus, and ABA and H2O2 treatments enhance the protein kinase activity of MPK12.
Together, these results provide genetic evidence that MPK9 and MPK12 function downstream of ROS to regulate guard cell ABA signaling positively.