RAS2 Regulates Growth and Pathogenesis in Fusarium graminearum

Abstract

Fusarium graminearum is a ubiquitous pathogen of cereal crops, including wheat, barley, and maize. Diseases caused by F. graminearum are of particular concern because harvested grains frequently are contaminated with harmful mycotoxins such as deoxynivalenol (DON). In this study, we explored the role of Ras GTPases in pathogenesis. The genome of F. graminearum contains two putative Ras GTPase-encoding genes. The two genes (RAS1 and RAS2) showed different patterns of expression under different conditions of nutrient availability and in various mutant backgrounds. RAS2 was dispensable for survival but, when disrupted, caused a variety of morphological defects, including slower growth on solid media, delayed spore germination, and significant reductions in virulence on wheat heads and maize silks. Intracellular cAMP levels were not affected by deletion of RAS2 and exogenous treatment of the ras2 mutant with cAMP did not affect phenotypic abnormalities, thus indicating that RAS2 plays a minor or no role in cAMP signaling. However, phosphorylation of the mitogen-activated protein (MAP) kinase Gpmk1 and expression of a secreted lipase (FGL1) required for infection were reduced significantly in the ras2 mutant. Based on these observations, we hypothesize that RAS2 regulates growth and virulence in F. graminearum by regulating the Gpmk1 MAP kinase pathway.

Comparative genomics of MAP kinase and calcium–calcineurin signalling components in plant and human pathogenic fungi

“…Likewise, expression of a dominant active ras2 allele of M. grisea stimulated appressorium formation on non-inductive surfaces in the wild-type strain, but not in the pmk1 mutant, suggesting that Ras2 functions upstream of the Mst11-Mst7-Pmk1 cascade (Park et al, 2006). A similar signalling role for Ras2 was proposed in F. graminearum (Bluhm et al, 2007). In this study, Ras2 orthologues containing predicted palmitoyl and farnesyl groups at the C-terminus for membrane localization were identified in all fungal species studied.…”

FgVELB is associated with vegetative differentiation, secondary metabolism and virulence in Fusarium graminearum

“…Diseased wheat kernels were harvested from inoculated spikelets 20 dpi for the determination of DON production using a previously described protocol (Mirocha et al, 1998;Bluhm et al, 2007). The DON extracts were purified with PuriTox SR , DON column TC-T200 (Trilogy Analytical Laboratory, Missouri, USA), and the amount of F. graminearum DNA in each sample was determined using a quantitative real-time PCR method (Yin et al, 2009).…”

Morphogenetic Circuitry Regulating Growth and Development in the Dimorphic Pathogen Penicillium marneffei

“…2). The gasC orthologues, rasA, and cflA are also important for conidial germination in the taxonomically closest model fungus Aspergillus nidulans, in Botrytis cinerea, and in a variety of other fungal species (3,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21).…”