TITLE:
G protein and MAPK signaling pathways control the ability of Cochliobolus heterostrophus to exploit different carbon sources
AUTHORS:
Ofir Degani
KEYWORDS:
Cochliobolus; Carbon Sources; Extracellular Enzymes; G-Protein; MAPK; Plant Pathogen
JOURNAL NAME:
Advances in Biological Chemistry,
Vol.4 No.1,
February
27,
2014
ABSTRACT: Phytopathogenic fungi are heterotrophic organisms that
excrete a complex array of enzymes for digestion of plant host tissues.
Regulation and coordination of extracellular enzyme production, according to
growth conditions and fungus nutritional needs, may be controlled by
conserved eukaryotic signaling elements such as G-protein subunits and
mitogen-activated protein kinase (MAPK). These pathways are known to mediate a
complex set of responses in fungi involved in development, reproduction and
pathogenicity. Here, we used a series of mutants, deficient in G-protein α (cga1)
or/and β subunits or in MAPK, to test
their contribution to the ability of Cochliobolus heterostrophus to
utilize different carbon sources. In saprophytic culture, the G-protein α subunit mutant strains had WT levels
of cellulase, pectinase and protease degradation activities, but it grew
significantly slower on minimal medium containing maltose. This weakened ability implies an essential role of the CGA1 signaling in some poor
nutritional environments. Remarkably, the MAPK null mutant failed to achieve
the WT (and cga1) growth
rate on cellulose as a sole carbon and did not grow at all for the first seven
days of culture. An enzymatic activity test revealed that this strain
significantly reduced cellulose extracellular degradation activity when grew on
this medium. Deficiency in the MAPK encoding gene also led to reduced
ability to grow on pectin, protein sources and maltose as a sole carbon. The
evidence presented indicates a significant and nutrient-specific role of the
G-protein and MAPK pathways in mediating growth of this fungus in different
environments.