AUTHOR=Onyilo Francis , Tusiime Geoffrey , Chen Li-Hung , Falk Bryce , Stergiopoulos Ioannis , Tripathi Jaindra N. , Tushemereirwe Wilberforce , Kubiriba Jerome , Changa Charles , Tripathi Leena 

TITLE=Agrobacterium tumefaciens-Mediated Transformation of Pseudocercospora fijiensis to Determine the Role of PfHog1 in Osmotic Stress Regulation and Virulence Modulation

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.00830

DOI=10.3389/fmicb.2017.00830

ISSN=1664-302X

ABSTRACT=<p>Black Sigatoka disease, caused by <italic>Pseudocercospora fijiensis</italic> 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 <italic>Saccharomyces cerevisiae</italic> 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 <italic>PfHog1</italic> gene on osmotic stress adaptation and virulence of <italic>P. fijie</italic>nsis. RNA interference-mediated gene silencing of <italic>PfHog1</italic> significantly suppressed growth of <italic>P. fijiensis</italic> on potato dextrose agar media supplemented with 1 M NaCl, indicating that <italic>PfHog1</italic> regulates osmotic stress. In addition, virulence of the <italic>PfHog1</italic>-silenced mutants of <italic>P. fijiensis</italic> 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 <italic>PfHog1</italic> in the infected leaf tissues, which was further confirmed with quantification of the fungal biomass using absolute- quantitative PCR. Collectively, these findings demonstrate that <italic>PfHog1</italic> plays a critical role in osmotic stress regulation and virulence of <italic>P. fijiensis</italic> on its host banana. Thus, <italic>PfHog1</italic> could be an interesting target for the control of black Sigatoka disease in banana.</p>