The Arabidopsis thaliana Mitogen-activated protein kinase (MAPK) phosphatase PP2C5 affects seed germination, stomatal aperture and abscisic acid-inducible gene expression.
Abscisic acid (ABA) is an important phytohormone regulating various cellular processes in plants, including stomatal opening and seed germination. Although protein phosphorylation via mitogen-activated protein kinases (MAPKs) has been suggested to be important in ABA signalling, the corresponding phosphatases are largely unknown. Here we show that a member of the PP2C family in Arabidopsis, PP2C5, is acting as a MAPK phosphatase. The PP2C5 protein co-localizes and directly interacts with stress-induced MPK3, MPK4 and MPK6 predominantly in the nucleus. Importantly, altered PP2C5 levels affect MAPK activation. Whereas Arabidopsis plants depleted of PP2C5 show an enhanced ABA-induced activation of MPK3 and MPK6, ectopic expression of PP2C5 in tobacco resulted in the opposite effect with the two MAPKs salicylic acid-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK) not being activated any longer after ABA treatment. Moreover, depletion of PP2C5, whose gene expression itself is affected by ABA treatment, resulted in altered ABA responses. Loss-of-function mutation in PP2C5 or AP2C1, a close PP2C5 homolog, resulted in an increased stomatal aperture under normal growth conditions and a partial ABA insensitive phenotype in seed germination which was most prominent in the pp2c5 ap2c1 double mutant line. In addition, response of ABA-inducible genes such as ABI1, ABI2, RD29A and Erd10 was reduced in the mutant plants. Thus, we suggest that PP2C5 acts as a MAPK phosphatase that positively regulates seed germination, stomatal closure and ABA-inducible gene expression.
Brock, A.K.; Willmann, R.; Kolb, D.; Grefen, L.; Lajunen, H.M.; Bethke, G.; Lee, J.; Nürnberger, Th.; Gust, A.A. 2010. The Arabidopsis thaliana Mitogen-activated protein kinase (MAPK) phosphatase PP2C5 affects seed germination, stomatal aperture and abscisic acid-inducible gene expression. Plant Physiology 153, 1098-1111.