Mitogen-Activated Protein Kinase Cascades in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 359

Fig. 7.7 Role of MPK3 and
MPK6 signaling cascade in
triggering biosynthesis of
camalexin in Arabidopsis
(Adapted from Ren et al.
2008 )

MAPKKKα/MEKK1

Phosphorylation

MKK4/MKK5

Phosphorylation

MPK3/MPK6

Phosphorylation

Transcription factors

Gene activation

ASA, ASB, PAT,IGPS,
TSA, TSB, CYP79B2,
CYP71A13, PAD3

Camalexin

have been shown to act as innate immunity gates to actively prevent bacteria from
entering the plant leaf (Melotto et al. 2006 ). The PAMP fl g22 triggers closure of
stomata which occurs within the fi rst hour of contact with plant tissue (Melotto et al.
2006 ). The PAMP-triggered stomatal closure was dependent on several signals and
signaling systems. The PAMP-induced ABA signaling system has been reported to
be involved in stomatal closure (Hubbard et al. 2010 ). ABA increase was the critical
early event in stomatal closure induced by fl g22 (Melotto et al. 2006 ). ROS signal-
ing system is also involved in the stomatal closure. ABA and H 2 O 2 treatments
induced inhibition of stomatal opening or the promotion of stomatal closure
(Gudesblat et al. 2007 ; Jammes et al. 2009 , 2011 ; Hettenhausen et al. 2012 ). NO
production, activation of OST1 (for O PEN ST OMATA 1 ) kinase, Ca 2+ infl ux, and
modulation of S-type anion channel have been found to be important for induction
of stomatal closure responses (Melotto et al. 2006 ; Vahisalu et al. 2008 ; Kim et al.
2010 ). Flg22 triggered ABA synthesis, NO production, and OST1 (for O PEN
ST OMATA 1 ) kinase, which are required for stomatal closure (Melotto et al. 2006 ).