The MKK2 Pathway Mediates Cold and Salt Stress Signaling in Arabidopsis

Abstract

The Arabidopsis mitogen-activated protein kinase (MAPK) kinase 2 (MKK2) and the downstream MAPKs MPK4 and MPK6 were isolated by functional complementation of osmosensitive yeast mutants. In Arabidopsis protoplasts, MKK2 was specifically activated by cold and salt stress and by the stress-induced MAPK kinase kinase MEKK1. Yeast two-hybrid, in vitro, and in vivo protein kinase assays revealed that MKK2 directly targets MPK4 and MPK6. Accordingly, plants overexpressing MKK2 exhibited constitutive MPK4 and MPK6 activity, constitutively upregulated expression of stress-induced marker genes, and increased freezing and salt tolerance. In contrast, mkk2 null plants were impaired in MPK4 and MPK6 activation and were hypersensitive to salt and cold stress. Full genome transcriptome analysis of MKK2-overexpressing plants demonstrated altered expression of 152 genes involved in transcriptional regulation, signal transduction, cellular defense, and stress metabolism. These data identify a MAP kinase signaling cascade mediating cold and salt stress tolerance in plants.

MAPK cascades and major abiotic stresses

“…A potential MAP kinase signaling pathway mediating salt stress responses, composed of MEKK1, MKK2 and the interchangeable MPK4/MPK6 genes, was previously identified in Arabidopsis (Teige et al 2004). Transgenic plants overexpressing MKK2 exhibit constitutive upregulation of stress marker genes and show enhanced salt tolerance.…”

“…The previously mentioned MAPK cascade (composed of MEKK1, MKK2 and MPK4/MPK6), which functions in salt stress signaling in Arabidopsis, is also functional in cold stress pathway (Teige et al 2004). The mkk2 mutant presents a freezing sensitive phenotype with no observable activity neither for MPK4 nor MPK6, suggesting that MKK2 is an upstream activator of MPK4 and MPK6 in cold signaling.…”

“…Table 1 summarizes a list of MAP kinase genes involved in the responses to multiple abiotic stresses in different plant species, based on changes in transcriptional regulation and/or enzymatic activities. Cold, salinity, dehydration Mizoguchi et al (1996), Moustafa et al (2008), Teige et al (2004) AtMPK4 AtMPK20 Table 1, an inferred MAP kinase cascade can be designed (Fig. 1) and tested in future research for the assessment of plant tolerance to abiotic stresses.…”

Plant Stress Surveillance Monitored by ABA and Disease Signaling Interactions

“…Moreover MAPK pathways have been reported to be a part of abiotic stress or ABA signal transduction. Besides a role in disease signaling, the MAP kinase kinase, MKK2 was reported to function as a negative regulator of cold and salt stress signal transduction (Teige et al, 2004). In contrast, guard cell preferentially expressed MPK9 and MPK12 act as positive regulators of ABA signaling at downstream of ROS and Ca 2+ signals and upstream of S-type anion channel regulation (Jammes et al, 2009).…”

Identification of Constitutively Active AtMPK6 Mutants Using a Functional Screen in Saccharomyces cerevisiae

“…Single and double mutants of the pathway are hypersensitive to salt and will die on high salt concentrations. In a previous work, we showed that a number of MAP2K/MAPK modules, including Arabidopsis AtMKK2/AtMPK6, are able to functionally complement the defect of growth of pbs2Δhog1Δ double mutants [ 4 ].…”