PAMP Signaling in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 62

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Wild type pbl1 mutant bik1 mutant pbl1/bik1 mutant

Fig. 2.2 Flg22-induced oxidative burst in bik1 , pbl1 , and bik1 / pbl1 mutant Arabidopsis plants
(Adapted from Zhang et al. 2010a )

Flg22-induced oxidative burst has been shown to be reduced in pbl1 mutant
Arabidopsis plants and the reduction was more in pbl1 and bik1 double mutant
plants, suggesting that PBL1 acts additively with BIK1 in plant innate immune
system (Fig. 2.2 ; Zhang et al. 2010a ).
PBL1 interacts with unstimulated FLS2 and is phosphorylated upon fl g22 stimu-
lation (Zhang et al. 2010a ). In addition to phosphorylation, fl g22 induces a dissocia-
tion of PBL1 from FLS2 (Zhang et al. 2010a ). The dissociation of the phosphorylated
PBL1 and also phosphorylated BIK1 from FLS2 allows the activation of other com-
ponents downstream of BIK1 and PBL1 (Lu et al. 2010 ; Zhang et al. 2010a ). BIK1
and, to a lesser extent, PBL1, PBL2, and PBS1, are required for signaling from
multiple PAMPs. BIK1, and likely PBS1 and other PBL proteins, directly act down-
stream of FLS2, EFR, CERK1 to trigger immune responses. Thus, the PBL1 and
PBS1 proteins are key components that integrate signaling from multiple immune
receptors. It appears that BIK1, PBL1, PBL2, and PBS1, integrate immune signal-
ing from multiple PRRs (Zhang et al. 2010a ).

2.12.8 ERECTA Protein

ERECTA, a LRR- receptor-like protein kinase, is encoded by erecta ( er ) gene
identified in Arabidopsis Landsberg erecta ecotype (Godiard et al. 2003 ). It is
a member of the RLK family of transmembrane proteins with a conserved cyto-
plasmic serine/threonine kinase domain and a divergent extracellular LRR
domain. ERECTA has been shown to interact with LRR-RLKs involved in
plant innate immunity, potentially PRRs (Godiard et al. 2003 ; Llorente et al.
2005 ). It is suggested that ERECTA may function in signal perception and/or
in transduction (Godiard et al. 2003 ). It is involved in triggering resistance
against the necrotrophic fungus Plectosphaerella cucumerina (Llorente et al.
2005 ) and the bacterium Ralstonia solanacearum in Arabidopsis (Godiard