Induced expression of selected plant defence related genesin pot azalea, Rhododendron simsii hybrid

A set of putative marker genes to study
plant defense responses against Polyphagotarsonemus
latus, a key pest in the production of Rhododendron
simsii hybrids, was selected and validated. Genes
belonged to the biosynthetic pathway of phytohormones
jasmonic acid (JA) (RsLOX, RsAOS, RsAOC,
RsOPR3 and RsJMT) and salicylic acid (SA) (RsPAL
and RsICS). Furthermore, RsPPO, a putative marker
gene for oxidative stress response was successfully
cloned from R. simsii. A CTAB-based extraction
protocol was optimized to assure excellent RNA quality for subsequent RT-qPCR analysis. The RTqPCR
protocol was extensively tested and RsRG7 and
RsRG14 were selected as reference genes from a
geNorm pilot study. Validation of the marker genes
was done after application with elicitors [methyl
jasmonate (MeJA), coronatine, b-aminobutyric acid
and acibenzolar-Smethyl] or wounding. Both 100 lM
MeJA and 0.1 lM coronatine had a significant effect
on the expression of all marker genes. Foliar application
of MeJA on the shoots resulted in a significantly
earlier response when compared to root application
and subsequent sampling of the shoots. Expression
patterns after MeJA treatment were generally the same
in six R. simsii genotypes: ‘Nordlicht’, ‘Elien’, ‘Aiko
Pink’, ‘Michelle Marie’, ‘Mevrouw Gerard Kint’ and
‘Sachsenstern’. Wounding resulted in the same
expression patterns as MeJA treatment except for
RsJMT. None of the genotypes showed a significant
induction of the latter gene 6 h upon wounding.
Findings of these experiments indicated that the tolerant genotype ‘Elien’ has low basal expression
levels of RsPPO. This might be the first step towards
the breeding of mite-tolerant genotypes.