Full Journal - Journal of Cell and Molecular Biology - Haliç Üniversitesi

98 Figen Mert-Türk and Eric B. Holub
a b
c d
e f
Figure 1: The interaction phenotypes between the
isolates of Peronospora parasitica and the lines of
Arabidopsis thaliana. Nd-1 (a) exhibited PN (pitting with
no pathogen sporulation phenotypes) after inoculation with
the Emoy2 isolate. However, Col-pad3 was more
susceptible than wild-type accession Col-0 following
inoculation with the same isolate and exhibited medium
sporulation (b). The response of Nd-pad3 to Emoy2 was
same as the Nd-1 parent (c). Flecking host response with no
sporulation was observed in Nd-1 (d) following inoculation
with any RPP13-avirulent isolate (d). Col-pad3 was fully
susceptible as it does not have a functional resistance gene
to recognise the isolates (e). The Nd-pad3, however,
exhibited the same interaction phenotype observed in Nd-1
parent (f).
These results indicate that PAD3 is not required for
resistance mediated by either RPP1 or RPP13 genes
against to the corresponding isolates of
P. parasitica, therefore, camalexin is not an essential
defence component for either source of downy
mildew resistance. Therefore, phytoalexin deficient
Nd-1 has only camalexin disability but still keeps
other known defence molecules for protecting itself
from pathogen.
Because the Col-pad3 mutant was more
susceptible than wild-type accession Col-0 following
inoculation with the isolate Emoy2, the result might
suggest that camalexin accumulation is important but
not enough in protection Col-0 from Emoy2. Col-0
recognises the avirulence product of P. parasitica
with RPP4 resistance gene. Therefore RPP4 is likely
camalexin-dependent.
Thomma et al. (1999) reported that resistance of
the Col-pad3 mutant to Botrytis cinerea is not altered
relative to that of wild-type. When Col-pad3
inoculated with Alternaria brassicicola, however, it
exhibited enhanced susceptibility compared to the
wild-type suggesting a role for PAD3 in resistance to
A. brassicicola. This finding proved that camalexin is
an important defence components. The same research
group also reported that PR1, therfore SA, and also
jasmonate/ethylene-dependent defence responses
were not impaired in the Col-pad3 mutant following
inoculation with A. brassicicola. Therefore camalexin
production appears to be controlled by a pathway that
exhibits little or no cross-talk with salicylate-,
ethylene-, and jasmonate-dependent signalling
events.
Acknowledgement
This research was supported financially by Turkish
Higher Educational Council (YOK) and Çanakkale
Onsekiz Mart University, Turkey. This article is
dedicated to first author’s parents for their
ever-lasting help and support during her education.
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