Mitogen-Activated Protein Kinase Cascades in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 354

Fig. 7.6 Role of MAPK
signaling cascade in
triggering ethylene
biosynthesis in Arabidopsis
(Adapted from: Li et al.
2012 )

Pathogen signal

Receptor

MAPKKK/MEKK1

Phosphorylation

MKK4/5

Phosphorylation

MPK3/MPK6

WRKY33

Phosphorylation

Stabilization of ACS2, ACS6
proteins

Binding to W-boxes in the
ACS2/ACS6 promoters

Increases in ACS activity

Activation of
ACS activity

Ethylene production

7.17 Involvement of MAP Kinase in Crosstalk Between SA

and JA/ET Signaling Systems

Crosstalk between SA and JA/ET signaling systems has been reported in different
plant-pathogen interactions. The tobacco basic PR protein gene NtPRB1b responds
positively to JA and ET signaling systems, but negatively to SA (Li et al. 2012 ). The
MAP kinase MPK4 plays a role in the antagonism between SA and JA signaling
systems in Arabidopsis thaliana . The mpk4 knockout plants exhibit constitutive
activation of SA-dependent signaling system, but fail to induce JA-dependent
signaling system (Petersen et al. 2000 ; Brodersen et al. 2006 ).
EDS1 and PAD4 are defense regulators and they modulate SA/JA signal antago-
nism as activators of SA but repressors of JA signaling (Wiermer et al. 2005 ;
Brodersen et al. 2006 ). The function of EDS1 and PAD4 in the antagonistic interaction
between SA and JA depends on the MAP kinase, MPK4 (Brodersen et al. 2006 ).