Changes in novel candidate defense genes profiling of leaves and root
collars of cucumber in response to Phytophthora melonis
Abstract
Phytophthora melonis is the causal agent of damping-off or crown rot,
one of the most destructive cucumber disease that causes severe economic
losses in in Iran and some other parts of the world. Despite intense
research efforts made in the past years, no permanent cure currently
exists for this disease. With the aim to understand the molecular
mechanisms of defense against P. melonis, root collars and leaves of
four cucumber genotypes consisting of resistant Ramezz; moderately
resistant Baby and very susceptible Mini 6-23 and Extrem, were monitored
for quantitative gene expression analysis of five antifungal and/or
anti-oomycete genes (CsWRKY20, CsLecRK6.1, PR3, PR1-1a and LOX1) at
three points after inoculation with P. melonis. The gene expression
analysis indicated that P. melonis strongly enhanced the expression of
these genes after inoculation in both leaves and root collars. Further,
not only the transcript levels of these genes were significantly higher
in the resistant and moderately resistance genotypes, but also the time
point of the highest relative expression ratio for the five genes was
different in the four cucumber genotypes. CsWRKY20 and PR3 showed the
maximum expression in Ramezz at 48 hpi while CsLecRK6.1, and LOX1 showed
the highest expression at 72 hpi. In addition, PR1-1a showed the maximum
expression in the Baby at 72 hpi. Root collars responded faster than
leaves and some responses were more strongly upregulated in root collars
than in leaves. The genes found to be involved in disease resistance in
two different organs of cucumber after pathogen infection. The results
suggest that increased expression of these genes led to activation of
defence pathways and could be responsible for a reduced P. melonis
colonization capacity in Ramezz and Baby. Overally, this work represents
a valuable resource for future functional genomics studies to unravel
the molecular mechanisms of C. sativus- P. melonis interaction.