Fruiting body development in Coprinus cinereus: regulated expression of two galectins secreted by a non-classical pathway

Fruiting body formation in the basidiomycete Coprinus cinereus is a develop mental process that occurs as a response of the mycelium to external stimul i. First, localized, highly branched hyphal structures (knots) are formed a s a reaction to nutritional depletion. Hyphal-knot formation is repressed b y light; however, light signals are essential for the development of the hy phal knot into an embryonic fruiting body (primordium) as well as karyogamy , meiosis and fruiting body maturation. The role of the different environme ntal signals in the initial phases of fruiting body development was analyse d. It was observed that two fungal galectins, Cgl1 and Cgl2, are differenti ally regulated during fruiting body formation. cgl2 expression initiated in early stages of fruiting body development (hyphal knot formation) and was maintained until maturation of the fruiting body, whereas cgl1 was specific ally expressed in primordia and mature fruiting bodies. Immunofluorescence and immunoelectron microscopy studies detected galectins within specific fr uiting body tissues. They localized in the extracellular matrix and the cel l wall but also in membrane-bound bodies in the cytoplasm. Heterologous exp ression of Cgl2 in Saccharomyces cerevisiae indicated that secretion of thi s protein occurred independently of the classical secretory pathway.