TITLE:
Pathogenicity Assay for Cochliobolus heterostrophus G-Protein and MAPK Signaling Deficiency Strains
AUTHORS:
Ofir Degani
KEYWORDS:
Cochliobolus heterostrophus; G-Protein; Maize; MAPK; Signal Transduction; Virulence
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.5 No.9,
April
16,
2014
ABSTRACT: Cochliobolus heterostrophus is an
agriculturally important and emerging model pathogen for studying the signaling
hierarchies' role during the maize host colonization. In particular, G-protein
and MAPK-linked pathways are playing a major role during pathogenesis. Although
gene disruption studies are an efficient way of identifying the role of these
cascades, differentiating between the mutant strains’ virulence ability may
become an intricate task. For example, in C. heterostrophus, mutants in
a G-protein α subunit gene, cga1,
are defective in mating and appressorium formation, but unlike mutants in
homologous genes in other fungal pathogens, the cga1 mutants remained
highly virulent to corn under some host physiological conditions. Here, we used
the cga1 strain as a model for developing an in vivo sensitive
and accurate pathogenicity assay. A detailed and well controlled analysis of
wild type (WT) and cga1 pathogenic behavior revealed that detached
leaves are significantly more vulnerable to the disease than intact ones. In
intact leaves, cga1 mutants were less infective of maize under most
conditions. This difference was maximized when the first seedling leaf was
chosen for inoculation and when the infected leaves, with spores or mycelia
fragments droplets, were incubated for a period of four days. This optimal
condition set enabled us to classify the C.
heterostrophus G-protein signaling mutants deficient in α, β or both subunits in order
of decreasing virulence: WT > cga1> cgb1> cga1 cgb1. The method presented proved to be accurate and sensitive enough to identify
even slight variations in virulence. Moreover, it could be modified for use in
studies of other foliar phytoparasitic fungi.