A CDC42 Homologue in Claviceps purpurea Is Involved in Vegetative Differentiation and Is Essential for Pathogenicity

Abstract

Claviceps purpurea, a biotrophic pathogen of cereals, has developed a unique pathogenic strategy including an extended period of unbranched directed growth in the host's style and ovarian tissue to tap the vascular system. Since the small GTPase Cdc42 has been shown to be involved in cytoskeleton organization and polarity in other fungi, we investigated the role of Cdc42 in the development and pathogenicity of C. purpurea. Expression of heterologous dominant-active (DA) and dominant-negative (DN) alleles of Colletotrichum trifolii in a wild strain of C. purpurea had significant impact on vegetative differentiation: whereas DA Ctcdc42 resulted in loss of conidiation and in aberrant cell shape, expression of DN Ctcdc42 stimulated branching and conidiation. Deletion of the endogenous Cpcdc42 gene was not lethal but led to a phenotype comparable to that of DN Ctcdc42 transformants. ⌬Cpcdc42 mutants were nonpathogenic; i.e., they induced no disease symptoms. Cytological analysis (light microscopy and electron microscopy) revealed that the mutants can penetrate and invade the stylar tissue. However, invasive growth was arrested in an early stage, presumably induced by plant defense reactions (necrosis or increased production of reactive oxygen species), which were never observed in wild-type infection. The data show a significant impact of Cpcdc42 on vegetative differentiation and pathogenicity in C. purpurea.

The Cryptococcus neoformans Rho-GDP Dissociation Inhibitor Mediates Intracellular Survival and Virulence

“…For example, in the rye pathogen Claviceps purpurea, a ⌬cdc42 strain was nonpathogenic in the absence of morphological and host invasion defects (50). Since Rdi1 interacts with Cdc42 in C. neoformans, it may be that the loss of Rdi1 repression in C. neoformans destabilizes Cdc42 function sufficiently to disrupt growth and polarization signals mediated by this protein when encountering the host environment.…”

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

“…Investigation of several Cdc42 orthologs (660)(661)(662)(663) demonstrated that Cdc42 is not required for plant penetration but is involved in early stages of plant colonization and that the deletion mutants of cdc42 are unable to survive in the host plant postpenetration (660). In U. maydis, the Cdc42 signaling network (including its GEF DON1; TR_120482, TA_234463, and TV_160649) and its downstream effector DON3 (TR_71315, TA_215231, and TV_ 208567) are required for appropriate septum formation and in appressorium development (664-666), but not necessarily for polarized growth (661).…”

Small-GTPase-Associated Signaling by the Guanine Nucleotide Exchange Factors CpDock180 and CpCdc24, the GTPase Effector CpSte20, and the Scaffold Protein CpBem1 in Claviceps purpurea

“…In the first infection stage, the strict polarity of the hyphal growth partly resembles pollen tube growth, which, together with a possible secretion of effector proteins, might be instrumental for nonrecognition. However, the paths of pollen tubes and infection structures in the ovary differ slightly (5,6).…”

“…CpCdc42 is a negative regulator of polarity and sporulation. Due to the defects in polarity during infection, the ⌬cpcdc42 strain is probably recognized as a pathogen by the plant (6). In contrast, CpRac is a positive mediator of polarity, sporulation, and general growth and is essential for infection (15).…”