The Transient Receptor Potential (TRP) Channel Family in Colletotrichum graminicola: A Molecular and Physiological Analysis

Abstract

Calcium (Ca2+) is a universal second messenger in all higher organisms and centrally involved in the launch of responses to environmental stimuli. Ca2+ signals in the cytosol are initiated by the activation of Ca2+ channels in the plasma membrane and/or in endomembranes. Yeast (Saccharomyces cerevisiae) contains a Ca2+-permeable channel of the TRP family, TRPY1, which is localized in the vacuolar membrane and contributes to cytosolic free Ca2+ ([Ca2+]cyt) elevations, for example in response to osmotic upshock. A TRPY1 homologue in the rice blast fungus is known to be important for growth and pathogenicity. To determine the role of the TRP channel family in the maize pathogen Colletotrichum graminicola, proteins homologous to TRPY1 were searched. This identified not one, but four genes in the C. graminicola genome, which had putative orthologs in other fungi, and which we named CgTRPF1 through 4. The topology of the CgTRPF proteins resembled that of TRPY1, albeit with a variable number of transmembrane (TM) domains additional to the six-TM-domain core and a diverse arrangement of putatively Ca2+-binding acidic motifs. All CgTRPF genes were expressed in axenic culture and throughout the infection of maize. Like TRPY1, all TRPF proteins of C. graminicola were localized intracellularly, albeit three of them were found not in large vacuoles, but co-localized in vesicular structures. Deletion strains for the CgTRPF genes were not altered in processes thought to involve Ca2+ release from internal stores, i.e. spore germination, the utilization of complex carbon sources, and the generation of tip-focussed [Ca2+]cyt spikes. Heterologous expression of CgTRPF1 through 4 in a tryp1Δ yeast mutant revealed that none of the channels mediated the release of Ca2+ in response to osmotic upshock. Accordingly, aequorin-based [Ca2+]cyt measurements of C. graminicola showed that in this fungus, osmotic upshock-triggered [Ca2+]cyt elevations were generated entirely by influx of Ca2+ from the extracellular space. Cgtrpf mutants did not show pathogenicity defects in leaf infection assays. In summary, our study reveals major differences between different fungi in the contribution of TRP channels to Ca2+-mediated signal transduction.

Transient receptor potential channels: current perspectives on evolution, structure, function and nomenclature

“…(i) TRPY and TRPF: the fungus-specific TRP channels TRPY1 was the first of the fungus-specific TRP channels to be discovered [10], a group that has since been expanded to include TRPF1-5 [8]. While a detailed structure of these channels has not been elucidated, TRPY1 is thought to form an intracellular Ca 2+ channel which gates in response to cytoplasmic Ca 2+ , osmotic shock, mechanical deformations and aromatic compounds [10,[129][130][131][132][133][134][135].…”

“…Like TRPY1, TRPF genes encode intracellular channels. They, however, do not gate Ca 2+ in response to osmotic shock, and it is unknown what functions TRPFs actively participate in [8].…”

“…While we have left the position of TRPY/TRPF unresolved with respect to Group 1 and Group 2 (figure 2), the hypothesis that they form a sister group to TRPP is parsimonious with the presence of various non-TRPP channels in non-fungal genomes. The position of TRPF channels in the wider TRP phylogeny has not been well resolved; they are likely to be very closely related to TRPY, and therefore to sort in the same position [8].…”

Allyl Isothiocyanate (AITC) Triggered Toxicity and FsYvc1 (a STRPC Family Member) Responded Sense in Fusarium solani

“…Transient receptor potential (TRP) channels are polymodal signal detectors that operate in response to a wide array of physical and chemical stimuli (Cordero-Morales et al, 2011). All TRP channels contain at least six transmembrane segments, highly unusual among known ion channel families, and exhibit diverse cation selectivity and specific activation mechanisms (Venkatachalam and Montell, 2007;Chang et al, 2010;Lange et al, 2016). TRP channels can be divided into three subfamilies based on homology: short (S), long (L), and osm (O).…”

“…In animal and human cell models, TRPA1 plays an important role in regulating channel activity and serves as a biosensor detecting O 2 (Takahashi et al, 2011); noxious environmental agents (Hinman et al, 2006), such as allicin and diallyl disulfide from garlic and cinnamaldehyde from cinnamon; acrolein, a common air pollutant; and cold or heat stimulation (Bautista et al, 2005(Bautista et al, , 2006Hinman et al, 2006). However, a few examples of TRP channels have been identified in fungi and non-land plants (Lange et al, 2016). Fungal TRPs form a distinct subfamily, distinct from the short, osm-like, and long subfamilies previously described in C. elegans, Drosophila melanogaster, human, and mouse studies (Denis and Cyert, 2002).…”