Proteomic analysis of proteins secreted by Botrytis cinerea in response to heavy metal toxicity

Although essential in many cellular processes, metals become toxic when they are present in excess and constitute a global environmental hazard. To overcome this stress, fungi have evolved several mechanisms at both intracellular and extracellular levels. In particular, fungi are well known for their ability to secrete a large panel of proteins. However, their role in the adaptation of fungi to metal toxicity has not yet been investigated. To address this question, here, the fungus Botrytis cinerea was challenged to copper, zinc, nickel or cadmium stress and secreted proteins were collected and separated by 2D-PAGE. One hundred and sixteen spots whose volume varied under at least one tested condition were observed on 2D gels. Densitometric analyses revealed that the secretome signature in response to cadmium was significantly different from those obtained with the other metals. Fifty-five of these 116 spots were associated with unique proteins and functional classification revealed that the production of oxidoreductases and cell-wall degrading enzymes was modified in response to metals. Promoter analysis disclosed that PacC/Rim101 sites were statistically over-represented in the upstream sequences of the 31 genes corresponding to the varying unique spots suggesting a possible link between pH regulation and metal response in B. cinerea.