Colletotrichum orbiculare WHI2, a Yeast Stress-Response Regulator Homolog, Controls the Biotrophic Stage of Hemibiotrophic Infection Through TOR Signaling

Abstract

The hemibiotrophic fungus Colletotrichum orbiculare first establishes a biotrophic infection stage in cucumber (Cucumber sativus) epidermal cells and subsequently transitions to a necrotrophic stage. Here, we found that C. orbiculare established hemibiotrophic infection via C. orbiculare WHI2, a yeast stress regulator homolog, and TOR (target of rapamycin) signaling. Plant defense responses such as callose deposition, H2O2, and antimicrobial proteins were strongly induced by the C. orbiculare whi2Δ mutant, resulting in defective pathogenesis. Expression analysis of biotrophy-specific genes evaluated by the promoter VENUS fusion gene indicated weaker VENUS signal intensity in the whi2Δ mutant, thereby suggesting that C. orbiculare WHI2 plays a key role in regulating biotrophic infection of C. orbiculare. The involvement of CoWHI2 in biotrophic infection was further explored with a DNA microarray. In the Cowhi2Δ mutant, TOR-dependent ribosomal protein-related genes were strikingly upregulated compared with the wild type. Moreover, callose deposition in the host plant after inoculation with the Cowhi2Δ mutant treated with rapamycin, which inhibits TOR activity, was reduced, and the mutant remained biotrophic in contrast to the untreated mutant. Thus, regulation of TOR by Whi2 is apparently crucial to the biotrophic stage of hemibiotrophic infection in C. orbiculare.

Whi2 is a conserved negative regulator of TORC1 in response to low amino acids

“…Down regulation of TORC1 in pathogenic strains of yeast such as Candida albicans and Candida glabrata is suggested to play a role in the persister state [ 67 ]. Consistent with our finding that Whi2 suppresses TORC1, the Whi2 ortholog in the fungal pathogen Colletotrichum orbiculare was recently suggested to have a role in plant pathogenesis by inhibiting TOR signaling [ 68 ].…”

UvWHI2 is Required for Stress Response and Pathogenicity in Ustilaginonidea Virens

“…This study analyzed the role of a general stress response factor Whi2 to reveal the relationship between the stress response and pathogenicity in U. virens. In yeast, the homolog of Whi2, ScWhi2, has been identified to be involved in various stress responses (Mendl et al, 2011, Harata et al, 2016, Teng et al, 2018. ScWhi2 interacts with the protein ScPsr1 to activate STRE-mediated genes, possibly via the dephosphorylation of the Msn2 transcription factor (Kaida et al, 2002, Boeckstaens et al, 2014, and then regulates the downstream stress response.…”

“…In Podospora anserina, the Whi2 homolog has been shown to control nutrient sensing and the entrance of cells into the stationary phase and mycelial development (Timpano et al, 2016). In Colletotrichum orbiculare, CoWHI2 was reported to play key roles in regulation of transition from biotrophic infection to necrotrophic infection via regulation of TOR (target of rapamycin) signaling, which is involved in the coordination of cell growth and proliferation with the availability of growth factors and nutrients (Harata et al, 2016). Until now, the function of Whi2 remains largly unknown in various organisms.…”

Chloramphenicol inhibits eukaryotic Ser/Thr phosphatase and infection-specific cell differentiation in the rice blast fungus

“…In Saccharomyces cerevisiae , Psr1p, the orthologue of MoDullard, co-functions with Whi2p and is involved in the sodium stress response 50,51 . The proteins Psr1 and Whi2 of Colletotrichum orbiculare , a plant pathogenic fungus that infects melons and cucumber, are associated with the target of rapamaycin (TOR) pathway and regulate pleiotropic cellular signalling 52 . The TOR pathway is broadly conserved among eukaryotes and regulates cell growth and proliferation in response to nutrients 53 .…”