Calcium Ion Signaling System: Calcium Signatures and Sensors - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 250

PAMP signal

Generation of cyclic nucleotide

Activation of CNG channels

Ca 2+ influx

Increase

Cytosolic
Ca 2+

Binding with
Ca 2+ sensor
protein
calmodulin

Binding with
CaM binding
protein NOS

Activation

NOS

Activation

NO

cGMP synthesis

Fig. 4.10 Amplifi cation of PAMP signal through Ca 2+ -triggered NO synthesis

and MPK6 by the P . syringae effector HopA/1 and inactivation of MKKs by the
P . syringae effector HopF2 severely impair PAMP-induced defenses and render
plants highly susceptible to nonpathogenic P . syringae bacteria (Zhang et al. 2007 ;
Wang et al. 2010 ). MPK3 and MPK6 have been shown to be required for priming of
defense responses during induced resistance (Beckers et al. 2009 ). The PAMPs are
known to activate the expression of MPK3, MPK4, and MPK6 (Asai et al. 2002 ;
Bethke et al. 2012 ).
A typical array of early defense responses induced by PAMPs includes Ca 2+ -
infl ux and the generation of ROS, nitric oxide, and ethylene. Much of this follows
the mitogen-activated protein kinase cascades, leading to transcriptional changes of
many defense-related genes (Zhang and Klessig 2001 ; Asai et al. 2002 ; Aslam et al.