Polyamine Metabolism in Fungi with Emphasis on Phytopathogenic Species

Polyamines are essential metabolites present in all living organisms, and this subject has attracted the attention of researchers worldwide interested in defining their mode of action in the variable cell functions in which they are involved, from growth to development and differentiation. Although the mechanism of polyamine synthesis is almost universal, different biological groups show interesting differences in this aspect that require to be further analyzed. For these studies, fungi represent interesting models because of their characteristics and facility of analysis. During the last decades fungi have contributed to the understanding of polyamine metabolism. The use of specific inhibitors and the isolation of mutants have allowed the manipulation of the pathway providing information on its regulation. During host-fungus interaction polyamine metabolism suffers striking changes in response to infection, which requires examination. Additionally the role of polyamine transporter is getting importance because of its role in polyamine regulation. In this paper we analyze the metabolism of polyamines in fungi, and the difference of this process with other biological groups. Of particular importance is the difference of polyamine biosynthesis between fungi and plants, which makes this process an attractive target for the control of phytopathogenic fungi. 1. Introduction Polyamines constitute a group of ubiquitous and essential aliphatic polycations found in both eukaryotic and prokaryotic organisms [1]. In higher eukaryotic organisms including fungi, the most common polyamines are putrescine, spermidine, and spermine; nevertheless, a large number of fungal species do not contain spermine. In general, it is accepted that the role of polyamines is to regulate several known and unknown biological processes. Polyamine depletion in the cells results in growth cessation [2, 3], whereas excessive intracellular accumulation of polyamines may be cytotoxic [4], indicating the necessity of a strict regulation of the intracellular polyamines pools. Addition of exogenous polyamines prolongs the life span of several organisms such as Saccharomyces cerevisiae, Caenorhabditis elegans, and Drosophila melanogaster [5]. In fungi, as occurs with the rest of living organisms, polyamines are essential to support growth, thus, mutants affected in their synthesis become auxotrophic to the missing polyamine. Additionally, they regulate a wide variety of biological phenomena including differentiation processes, for example, dimorphism, spore germination, and appressorium