Vacuolal and Peroxisomal Calcium Ion Transporters in Yeasts and Fungi: Key Role in the Translocation of Intermediates in the Biosynthesis of Fungal Metabolites.

Abstract

Highlights The intracellular calcium content plays a key role in the expression of genes involved in the biosynthesis and secretion of fungal metabolites.The cytosolic calcium concentration in fungi is maintained by influx through the cell membrane and by release from store organelles.Some MSF transporters, e.g., PenV of Penicillium chrysogenum and CefP of Acremonium chrysogenum belong to the TRP calcium ion channels.A few of the numerous calcium ion transporters existing in organelles of different filamentous fungi have been characterized at the functional and subcellular localization levels.The cytosolic calcium signal seems to be transduced by the calcitonin/calcineurin cascade controlling the expression of many fungal genes. The intracellular calcium content in fungal cells is influenced by a large number of environmental and nutritional factors. Sharp changes in the cytosolic calcium level act as signals that are decoded by the cell gene expression machinery, resulting in several physiological responses, including differentiation and secondary metabolites biosynthesis. Expression of the three penicillin biosynthetic genes is regulated by calcium ions, but there is still little information on the role of this ion in the translocation of penicillin intermediates between different subcellular compartments. Using advanced information on the transport of calcium in organelles in yeast as a model, this article reviews the recent progress on the transport of calcium in vacuoles and peroxisomes and its relation to the translocation of biosynthetic intermediates in filamentous fungi. The Penicillium chrysogenum PenV vacuole transporter and the Acremonium chrysogenum CefP peroxisomal transporter belong to the transient receptor potential (TRP) class CSC of calcium ion channels. The PenV transporter plays an important role in providing precursors for the biosynthesis of the tripeptide δ-(-α-aminoadipyl-L-cysteinyl-D-valine), the first intermediate of penicillin biosynthesis in P. chrysogenum. Similarly, CefP exerts a key function in the conversion of isopenicillin N to penicillin N in peroxisomes of A. chrysogenum. These TRP transporters are different from other TRP ion channels of Giberella zeae that belong to the Yvc1 class of yeast TRPs. Recent advances in filamentous fungi indicate that the cytosolic calcium concentration signal is connected to the calcitonin/calcineurin signal transduction cascade that controls the expression of genes involved in the subcellular translocation of intermediates during fungal metabolite biosynthesis. These advances open new possibilities to enhance the expression of important biosynthetic genes in fungi.