MAP kinases MPK9 and MPK12 are preferentially expressed in guard cells and positively regulate ROS-mediated ABA signaling

Abstract

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.abscisic acid ͉ anion channels ͉ protein kinase ͉ reactive oxygen species ͉ stomata

MAPK cascades and major abiotic stresses

“…A mapkkk knockout mutant of the Arabidopsis MAPKKK20 (MAP kinase kinase kinase) presents an improved salt tolerance, particularly in the later developmental stages (Gao and Xiang 2008). Additionally, the Arabidopsis double mutant mpk9/mpk12 loses water by transpiration less than the wild type (Jammes et al 2009). …”

Ethylene-Induced Flavonol Accumulation in Guard Cells Suppresses Reactive Oxygen Species and Moderates Stomatal Aperture

“…The gain settings were selected to maximize the total Hoechst signal while preventing oversaturation. ethylene gas for 24 h were excised and submerged in an aqueous opening solution (5 mM KCl, 50 mM CaCl 2 , 10 mM MES buffer, pH 5.6) and incubated under cool-white light for 3 h. To induce stomatal closure, leaves were transferred to a similar opening solution with 20 mM ABA added to induce closure (Jammes et al, 2009). After incubation in the ABA solution under white light (100 mmol m 22 s 22 ) for 0, 45, 90, and 180 min, leaf peels were prepared and imaged using DIC imaging with a Zeiss Axio Observer D1 microscope with a Hamamatsu 1394 ORCA-ERA monochromatic camera (Jammes et al, 2009).…”

Mining expressed sequence tags of rapeseed (Brassica napus L.) to predict the drought responsive regulatory network

“…ABI1 mediates signal transduction between ABA reception and ROS production under stress conditions (Murata et al 2001). The Previous studies indicated that MAP kinase signaling is activated following ROS accumulation, as testified to the induction of MPK3 and MPK6 by H 2 O 2 (Jammes et al 2009;Xing et al 2008). Interestingly, in this study, the expression of a B. napus homolog of MPK6 was significantly upregulated during drought stress.…”