Changes in synthesis and abundance of specific polypeptides at early and late stages of blue-light-induced sporulation of Trichoderma

Abstract

The temporal relationship between photoinduced morphogenesis and the translation and abundance of specific polypeptides was studied in Trichoderma harzianum. Sporulation of this common soil fungus is induced by a brief pulse of low fluence blue light. The minute light signal is amplified to cause a local switch from vegetative mycelia to the production of aerial, branched conidiophores. Patterns of polypeptide synthesis and abundance were analysed to detect changes both before and after visible structural changes occur. The early phases of morphogenesis (up to 4–8 h after light) occur without masive changes in morphology, or in the pattern of polypeptide abundance. Two-dimensional electrophoresis of polypeptides pulse labelled in vivo demonstrated that a major in vivo translation product at 65 kD and near neutral pH disappeared within 2 h after light and another labelled spot at slightly more acidic pH and 90 kD increased during the first 4 h after light. Major differences in polypeptide abundance were detected only when mature conidiophores were compared with vegetative mycelia. Four major soluble polypeptides were specific to vegetative mycelia, while two major polypeptides were specific to membrane fractions from conidiophores. A polyclonal antibody was obtained against the most abundant of these membrane proteins, a 48 kD polypeptide. The antibody recognized a 48 kD polypeptide on immunoblots of membrane fractions from sporulating colonies at 24 h after photoinduction, but not from dark control colonies of the same age. On immunoblots of total protein, the 48 kD polypeptide was detectable at 12–16 h after photoinduction, together with the completion of conidiophore branching, and increased further by 24 h, when pigmented spores are present.