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Calcium/Calmodulin-Dependent Signaling for Prepenetration Development in Colletotrichum gloeosporioides

Colletotrichum gloeosporioides forms a specialized infection structure, an appressorium, for host infection. Contacting hard surface induces appressorium formation in C. gloeosporioides, whereas hydrophobicity of the contact surface does not affect this infection-related differentiation. To determine if the calcium/calmodulin-dependent signaling system is involved in prepenetration morphogenesis in C. gloeosporioides pathogenic on red pepper, effects of calcium chelator (EGTA), phospholipase C inhibitor (neomycin), intracellular calcium modulators (TMB-8 and methoxy verampamil), and calmodulin antagonists (chloroproma-zine, phenoxy benzamine, and W-7) were tested on conidial germination and appressorium formation. Exogenous addition of Ca²⁺, regardless of concentration, augmented conidial germination, while appressorial differentiation decreased at higher concentrations. Inhibition of appressorium formation by EGTA was partly restored by the addition of calcium ionophore A23187 or CaCl₂. Calcium channel blockers and calmodulin antagonists specifically reduced appressorium formation at micromolar levels. These results suggest that biochemical processes controlled by the calcium/calmodulin signaling system are involved in the induction of prepenetration morphogenesis in C. gloeosporioides pathogenic on red pepper.