Identification of a second family of genes in Moniliophthora perniciosa, the causal agent of witches' broom disease in cacao, encoding necrosis-inducing proteins similar to cerato-platanins

The hemibiotrophic basidiomycete Moniliophthora perniciosa is the causal agent of witches' broom disease in cacao. This is a dimorphic species, with monokaryotic hyphae during the biotrophic phase, which is converted to dikaryotic mycelia during the saprophytic phase. The infection in pod is characterized by the formation of hypertrophic and hyperplasic tissues in the biotrophic phase, which is followed by necrosis and complete degradation of the organ. We found at least five sequences in the fungal genome encoding putative proteins similar to cerato-platanin (CP)-like proteins, a novel class of proteins initially found in the phytopathogen Ceratocystis fimbriata. One M. perniciosa CP gene (MpCP1) was expressed in vitro and proved to have necrosis-inducing ability in tobacco and cacao leaves. The protein is present in solution as dimers and is able to recover necrosis activity after heat treatment. Transcription analysis ex planta showed that MpCP1 is more expressed in biotrophic-like mycelia than saprotrophic mycelia. The necrosis profile presented is different from that caused by M. perniciosa necrosis and ethylene-inducing proteins (MpNEPs), another family of elicitors expressed by M. perniciosa. Remarkably, a mixture of MpCP1 with MpNEP2 led to a synergistic necrosis effect very similar to that found in naturally infected plants. This is the first report of a basidiomycete presenting both NEP1-like proteins (NLPs) and CPs in its genome. (C) 2008 The British Mycological Society. Published by Elsevier Ltd. All rights reserved.