structurally related to fatty acid synthetases [8]. They usually have in common a set of conserved domains that always include three basic ones: acyltransferase (AT), which recognizes the monomer that will be used in the synthesis; ketosynthase (KS), which joins it to the elongating polyketide chain; and acyl carrier protein (ACP), which has a prosthetic group of phosphopantetheine that serves as a covalent binding site for the intermediate formed in the synthesis. These are accompanied by other optional domains. The keto groups formed in the elongating process can be reduced by ketoreductase (KR), dehydatase (DH), or enol reductase (ER) domains to produce different modifications depending on the specific PK in question. There are other possible domains, e.g., methyl transferase (MT), or condensation/heterocyclization (HC), that can introduce additional changes. PKSs can be iterative or non-iterative. In iterative PKSs the macro-enzyme functions as an extension module that elongates the product in successive reactive cycles. These PKSs can be reducing or non-reducing depending on the presence of the reducing KR, DH, and ER domains. Non-iterative PKSs are usually multimodular, with each module having its own domain combination responsible for a complete elongation cycle, and with a final module with a releasing thioesterase (TE) domain [9]. The products resulting from the PKS activity are modified by other enzymes, giving rise to the vast chemical diversity that characterizes this family. Some well-known examples of PKs synthesized by type I PKSs are described in Table 1 and Figure 1. In some cases, two different PKSs participate in the synthesis of the same compound, as occurs with zearalenone [10]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Chemical Family**} & \multirow{2}{*}{**Metabolite**} & \multirow{2}{*}{**Function/Activity**} & \multicolumn{2}{c}{**Representative**} & \multirow{2}{*}{**Reference**} \\  & & & & **Producing Genera** & \\ \hline \multirow{6}{*}{Polyketides (PKs)} & Fumonisin B1 & Mycotoxin & _Fusarium_ & [11] \\  & Lovastatin & HMG-CoA reductase & _Aspergillus_ & [12] \\  & inhibitor & _Aspergillus_ & [13] \\  & Aflatoxin & Mycotoxin & _Aspergillus_ & [13] \\  & Bikaverin & Antibiotic (protozoa) & _Fusarium_ & [14] \\  & Zearalenone & Mycotoxin (estrogenic) & _Fusarium_ & [10] \\ \hline \multirow{6}{*}{Non ribosomal peptides (NRPs)} & Ennian B & Mycotoxin (cytotoxic) & _Fusarium_ & [15] \\  & Cyclosporine A & Immunosuppressant & _Tolypocadium_ & [16] \\ \cline{1-1}  & Ergotamine & Ergot alkaloid & _Claicyceps_ & [17] \\ \cline{1-1}  & Penicillin G & Antibiotic (bacteria) & _Penicillin_ & [18] \\ \cline{1-1}  & Apicidin & Histone deacetylase & _Fusarium_ & [19] \\ \hline \multirow{6}{*}{Hybrid NRP/PKs} & Equisetin & Antibiotic (bacteria) & _Fusarium_ & [20,21] \\ \cline{1-1}  & Fusarin C & Mycotoxin & _Fusarium_ & [22] \\ \cline{1-1}  & Cytochalasin & Actin inhibitor & _Penicillin_, _Chantonium_ & [23] \\ \cline{1-1}  & Cyclopiazonic acid & Mycotoxin & _Aspergillus_, _Penicillin_ & [24] \\ \cline{1-1}  & Ochratoxin A & Mycotoxin & _Aspergillus_, _Penicillin_ & [25,26] \\ \hline \multirow{6}{*}{Trepenoids} & Gibberellic acid (GA3) & Plant hormone & _Fusarium_ & [27,28] \\ \cline{1-1}  & Deoxynivalenol & Mycotoxin & _Fusarium_ & [29] \\ \cline{1-1}  & Neurosporaxanthin & Carotenoid pigment & _Neurospora_, _Fusarium_ & [30,31] \\ \cline{1-1}  & Austinol & Unknown & _Aspergillus_ & [32] \\ \cline{1-1}  & Helvolic acid & Antibiotic (bacteria) & _Aspergillus_ & [33] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A selection of fungal secondary metabolites. Five representative examples are indicated for each SM family. Type II PKSs are large multienzymatic complexes, combining a set of catalytic activities that act iteratively and that frequently produce aromatic compounds [34]. This class of enzymes is typically found in prokaryotes, and genome analyses indicate that they are absent in fungi. Type III PKSs are homodimeric enzymes of less diverse function.