Biology Reference
In-Depth Information
( CmCAL-1 ) was reported in spotted knapweed and dandelion within 15 min in
response to Nep1 (Keates et al. 2003 ).
The signaling cascade initiated by the HAMP AtPep1 leads to expression of
defense genes in a Ca 2+ -dependent manner (Qi et al. 2010 ). The endogenous
elicitor AtPep1 after binding with its PRR AtPepR1 activates plant membrane
inwardly conducting Ca 2+ permeable channels in mesophyll cells, resulting in
cytosolic Ca 2+ elevation. This activity is dependent on the PRR AtPepR1 as well
as a cyclic nucleotide-gated channel (CNGC2). The PRR AtPepR1 has guanylyl
cyclase activity and this activity generates cGMP from GTP. The cGMP activates
CNGC2-dependent cytosolic Ca 2+ elevation (Qi et al. 2010 ). AtPep-dependent
expression of defense genes such as PDF1.2 , MPK3 , and WRKY33 , is mediated
by the Ca 2+ signaling pathway associated with AtPep peptides and their receptor
(Qi et al. 2010 ). These studies indicate that downstream from AtPep and AtPepR1
in a signaling cascade, the cGMP-activated channel CNGC2 is involved in
AtPep- and AtPepR1- dependent inward Ca 2+ conductance and resulting cyto-
solic Ca 2+ elevation.
Although several PAMPs trigger Ca 2+ infl ux, some PAMPs are capable of eliciting
plant immune responses without triggering Ca 2+ infl ux (Lecourieux et al. 2002 ,
2006 ; Garcia-Brugger et al. 2006 ). Peptidoglycan and muropeptides are virtually
ineffective at inducing Ca 2+ infl ux, yet are capable of eliciting other defense
responses (Erbs et al. 2008 ). The role of Ca 2+ signaling system in plant innate immunity
is further described in Chap. 4 .
2.20.3
H + Fluxes and Extracellular Alkalinization
K + /H + exchange response is another important component in the plant immune
signaling system (Orlandi et al. 1992; Felix et al. 1999 ). The PAMPs have been
shown to trigger apoplastic alkalinization combined with cytosolic acidifi cation in
plant cells (Sakano 2001; Felle et al. 2004). Flagellin purifi ed from P . syringae pv.
tabaci is able to induce medium alkalinization in plant cell cultures from tomato,
tobacco, potato, and Arabidopsis (Felix et al. 1999 ). The Ca 2+ -dependent protein
kinase, activated by increased cytosolic Ca 2+ concentration may evoke H + fl uxes that
lead to extracellular alkalinization and depolarization of the plasma membrane
(Schaller and Oecking 1999).
The extracellular alkalinization is one of the earliest responses of suspension-
cultured cells to OGs. Alkalinization results from the inhibition of the plasma mem-
brane proton ATPases (PMA) via a signaling pathway that involves calcium ions
and a calcium-dependent protein kinase (Schaller and Oecking 1999). In plants,
PMA is the main electrogenic pump that generates the proton motive force across
the plasma membrane and PMA inhibition reduces ATP consumption. OG elicitor
signifi cantly controls proton pumps, K + channels, and H 2 O 2 production (Lecourieux
et al. 2005 , 2006 ).
Search WWH ::




Custom Search