Abstract:

Black Sigatoka disease, caused by Pseudocercospora fijiensis is a serious constraint
to banana production worldwide. The disease continues to spread in new ecological
niches and there is an urgent need to develop strategies for its control. The
high osmolarity glycerol (HOG) pathway in Saccharomyces cerevisiae is well known
to respond to changes in external osmolarity. HOG pathway activation leads to
phosphorylation, activation and nuclear transduction of the HOG1 mitogen-activated
protein kinases (MAPKs). The activated HOG1 triggers several responses to osmotic
stress, including up or down regulation of different genes, regulation of protein
translation, adjustments to cell cycle progression and synthesis of osmolyte glycerol.
This study investigated the role of the MAPK-encoding PfHog1 gene on osmotic
stress adaptation and virulence of P. fijiensis. RNA interference-mediated gene silencing
of PfHog1 significantly suppressed growth of P. fijiensis on potato dextrose agar
media supplemented with 1 M NaCl, indicating that PfHog1 regulates osmotic
stress. In addition, virulence of the PfHog1-silenced mutants of P. fijiensis on banana
was significantly reduced, as observed from the low rates of necrosis and disease
development on the infected leaves. Staining with lacto phenol cotton blue further
confirmed the impaired mycelial growth of the PfHog1 in the infected leaf tissues,
which was further confirmed with quantification of the fungal biomass using absolutequantitative
PCR. Collectively, these findings demonstrate that PfHog1 plays a critical
role in osmotic stress regulation and virulence of P. fijiensis on its host banana. Thus,
PfHog1 could be an interesting target for the control of black Sigatoka disease in
banana