Fungal lacatamases, what’s up with that??

We are determining the role of fungal lactamase encoding genes in the environmental competitiveness of Fusarium verticillioides (Fv), a fungus commonly infecting maize and producing the fumonisin mycotoxins. The role of bacterial β-lactamases as a mechanism of resistance to β-lactam antibiotics (such as penicillin) is well documented. Recently we documented the existence of large families of genes encoding metallo-β-lactamases (PFAM PF00753) and serine-based β-lactamases (PF00144) in some fungi. Interestingly, the genomes of soil borne fungi are highly enriched in lactamase encoding genes. For example, Fv has 46 genes, split roughly evenly between metallo- and serine- subtypes. In contrast, the environmentally isolated foliar obligate plant pathogens, such as wheat stem rust (Puccinia graminis), wheat powdery mildew (Blumeria graminis ), and peach leaf curl (Taphrina deformans) genomes encode only 5, 2, and 5 lactamases, respectively. Our central hypothesis is that in the microbially diverse soil environment fungi are exposed to numerous, mostly unidentified, xenobiotics that they must detoxify. We currently know the function of only one of the Fv lactamase genes. MBL1 (FVEG_08291) is required for degradation of the plant derived benzoxazinone phytoanticipins BOA and MBOA. Importantly, MBL1 expression is highly and specifically induced upon exposure to BOA. This then serves as our paradigm: lactamase genes induced by specific xenobiotics are predicted to confer resistance to the inducing xenobiotic. We are taking a broad approach to identify interactions that induce specific sets of Fv lactamases. Assays for expression of specific lactamases are underway and include interactions with soil isolated Streptomyces species and with Sarocladium zeae, a fungal co-inhabitant with Fv in maize seed. RNAseq results of the Fv-S. zeae interaction will be presented by Minglu Gao et al. We have generated a set of single lactamase gene deletion mutants to test the role of individual genes in conferring resistance to specific stimuli.