Genetic interaction and phenotypic analysis of the Arabidopsis MAP kinase pathway mutations mekk1 and mpk4 suggests signaling pathway complexity

Abstract

It has been shown that the Arabidopsis MEK kinase MEKK1 acts upstream of the MAP kinase MPK4 to negatively regulate salicylic acid-dependent defense-response pathways. Here, we report that the mekk1;mpk4 double-mutant combination causes seedling lethality. In addition, we demonstrate that mekk1 and mpk4 single-mutant plants have significantly different phenotypes. mekk1 plants are defective for lateral root formation, while mpk4 plants are not. In addition, treatment with elevated levels of sodium chloride improves the growth of mekk1 plants, while it inhibits the growth of mpk4 plants. Our results suggest that MEKK1 and MPK4 functions are not limited to a single, linear signaling pathway. Instead there appears to be more complexity to the signaling pathways in which these two proteins function.

Novel Functions of Stomatal Cytokinesis-Defective 1 (SCD1) in Innate Immune Responses against Bacteria

“…These immune phenotypes are reminiscent of those described for cpr mutants. But in contrast to most previously described mutants with cpr-like phenotypes (15,18,31,34,35), SCD1 has a role in plant growth and development per se. Using two independent approaches (blocking SA biosynthesis genetically by introducing the sid2-2 mutant allele into scd1-1 and shift to high temperature; Figs.…”

“…6B, p Յ 0.001). But in contrast to bon1-1 and other mutants with cpr-like phenotypes (15,18,31,34,35), growth impairment of scd1-1 was not rescued by shift to high temperature (Fig. 6A).…”

Salt-induced subcellular kinase relocation and seedling susceptibility caused by overexpression of Medicago SIMKK in Arabidopsis

“…It is well documented that both MPK6 and MPK3 are activated by NaCl stress, and their activation seems to be required for salt tolerance in A. thaliana (Ichimura et al , 2000; Droillard et al , 2002; Teige et al , 2004; Yu et al , 2010). High concentrations of salt activate MKKK20 in Arabidopsis , which is upstream of MPK6 (Kim et al , 2012), but in the MEKK1-dependent signalling pathway involving MPK4, mekk1 mutants exhibited improved growth under high salinity (Su et al , 2007). These results suggest that, in contrast to MKKK20, MEKK1 may negatively regulate the salt response in Arabidopsis .…”

Arabidopsis thaliana mitogen-activated protein kinase 6 is involved in seed formation and modulation of primary and lateral root development

“…Mutants having increased number of LRs are relatively infrequent compared with those with reduced number of LRs (De Smet et al , 2006), although an increased number of LRs does not necessary indicate an increase in LR initiation (Dubrovsky and Forde, 2012). The participation of MAPK cascades in LR formation was documented by the phenotypes observed in mutants of MPK4 and its upstream activator MEKK1-1, both displaying from a slight to a severe reduction in LR density (Nakagami et al , 2006; Su et al , 2007). Previous studies have also shown that MPK3 and MPK6 are activated in response to the same signals as MEKK1/MPK4, supporting a possible role of these kinases in the LR development programme (Ichimura et al , 2006; Suarez-Rodriguez et al , 2007).…”