Fusaric Acid Gene Cluster in Fusarium temperatum and Fusarium subglutinans and its Production under Different Culture Conditions

FUMERO VERONICA; TOOMAJIAN C; SULYOK M; LESLIE J.F.; CHULZE , S.N

Lima

Congreso; IX Congreso Latinoamericano de Micologia; 2017

Asociación Latinoamericana de Micologia

Fusaric acid (FA) is a secondary metabolite with low to moderate toxicity towards animalsand humans, but is highly phytotoxic. Fusaric acid is produced by several species in theFusarium fujikuroi species complex e.g., F. verticillioides, F. proliferatum, and F.subglutinans, and also by more distantly related Fusarium species, e.g., F. oxysporum and F.solani. Recently, the FA gene cluster was described for F. verticillioides, F. fujikuroi and F.oxysporum. The cluster includes 12 genes with only two, FUB1 (polyketide synthase) andFUB4 (hydrolase), hypothesized to be required to produce wild-type levels of the toxin. Athird gene, FUB12, encodes a C6 transcription factor that regulates the synthesis of aderivative, fusarinolic acid (FnA), and functions as a detoxification mechanism. Thesynthesis of FA and FnA are both dependent upon culture conditions. In the present studywe looked for this cluster in two species, F. subglutinans and F. temperatum, that are maizepathogens and that are more common in temperate to colder regions of the world. We alsoevaluated the influence of abiotic factors, e.g., temperature, water activity and incubationtime, on the production of FA and FnA. Both species have the 12 genes in the same orderand orientation as in F. fujikuroi, which differs from the orientation in F. verticillioides. Thesequences of the two main genes, FUB1 and FUB4, could be translated in silico into complete protein sequences. The nucleotide sequences of the flanking regions of the cluster were similar in F. subglutinans and F. temperatum, but differed in gene number, structure and orientation when compared to similar regions in F. fujikuroi and F. verticillioides. When the FA and FnA levels were measured, they varied between species and with abiotic conditions. For both species, the maximum levels of FnA were on average 10 times higher than the maximum levels of FA under similar conditions. Both species had different FA production profiles depending on the environmental conditions, but in general, F. temperatum produced more of this toxin than did F. subglutinans. For F. temperatum, water activity significantly (p<0.05) affected FA production, with the highest levels occurring at 0.995 aW, regardless of the temperature. For F. subglutinans, water activity, temperature and their interaction significantly (p<0.05) affected FA production, with the highest levels at 15 C and 25 C produced at 0.995aW, but the highest level at 30 C was produced at 0.98aW. For FnA, water activity, temperature and their interaction significantly (p<0.05) affected toxin production by both species. F. temperatum produced the most FnA at 0.995 aW and 30 C, while F. subglutinans produced the most at 0.995 aW and 25 C. In conclusion, there are a wide range of conditions for FA and FnA production by F. temperatum and F. subglutinans. Thus, their presence could represent a toxicological risk and reduce the quality of maize grain. Since toxin production depended upon environmental conditions, additional studies of the genetic regulation of the Fusaric Acid gene cluster are required to fully understand the role of abiotic factors in the production of these secondary metabolites.