Transcriptome analysis of Aspergillus flavus reveals veA-dependent regulation of secondary metabolite gene clusters, including the novel aflavarin cluster

Authors: Cary, Jeffrey; HAN, ZHENG - Ghent University; YIN, Y - Northern Illinois University; LOHMAR, JESSICA - Northern Illinois University; SHANTAPPA, SOURABHA - Northern Illinois University; Harris Coward, Pamela; Mack, Brian; EHRLICH, KENNETH - Retired ARS Employee; Wei, Qijian - Mei Mei; ARROYO-MANZANARES, N - Ghent University; UKA, VALDET - Ghent University; VANHAECKE, LYNN - Ghent University; Bhatnagar, Deepak; Yu, Jiujiang; NIERMAN, WILLIAM - J Craig Venter Institute; JOHNS, M - Northern Illinois University; SORENSEN, D - Northern Illinois University; SHEN, H - Northern Illinois University; DE SAEGER, SARAH - Ghent University; DIANA DI MAVUNGU, J - Ghent University; CALVO, ANA - Northern Illinois University

Submitted to: Eukaryotic Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2015
Publication Date: 10/15/2015
Citation: Cary, J.W., Han, Z., Yin, Y., Lohmar, J.M., Shantappa, S., Harris-Coward, P.Y., Mack, B.M., Ehrlich, K.C., Wei, Q., Arroyo-Manzanares, N., Uka, V., Vanhaecke, L., Bhatnagar, D., Yu, J., Nierman, W.C., Johns, M., Sorensen, D., Shen, H., De Saeger, S., Diana Di Mavungu, J., Calvo, A.M. 2015. Transcriptome analysis of Aspergillus flavus reveals veA-dependent regulation of secondary metabolite gene clusters, including the novel aflavarin cluster. Eukaryotic Cell. 14(10):983-997. doi: 10.1128/EC.00092-15.

Interpretive Summary: Using microarray technology we were able to look at the differences in expression of genes between a velvet (veA) gene mutant of the fungus Aspergillus flavus and that of a non-mutated (wild-type) strain. Of particular interest was the finding that gene expression in a number of predicted secondary metabolite gene clusters were downregulated in the veA mutant compared to the wild-type. Filamentous fungi, including Aspergillus flavus, produce a number of secondary metabolic compounds that have been shown to be both of great value (i.e. antibiotics and anti-hypercholesterolemics) and great harm (i.e. aflatoxins and trichothecenes). The genes responsible for producing a particular secondary metabolite are often clustered together on the chromosome. We have identified a secondary metabolic cluster in the fungus Aspergillus flavus and shown it is responsible for the production of the compound, aflavarin. We showed the gene cluster responsible for aflavarin production is under the control of the global regulator, VeA. Aflavarin is found mainly in the survival structures known as sclerotia and this metabolite probably plays a role in reducing insect predation on sclerotia in the field.

Technical Abstract: The global regulatory veA gene governs development and secondary metabolism in numerous fungal species, including Aspergillus flavus. This is especially relevant since A. flavus infects crops of agricultural importance worldwide, contaminating them with potent mycotoxins. The most well-known are aflatoxins, cytotoxic and carcinogenic polyketide compounds. The production of aflatoxins, and the expression of genes implicated in the production of these mycotoxins, are veA-dependent. The genes responsible in the synthesis of aflatoxins are clustered, a signature common for genes involved in the synthesis of fungal secondary metabolites. Studies of the A. flavus genome revealed many gene clusters possibly connected to the synthesis of secondary metabolites. Many of these metabolites are still unknown, or the association between a known metabolite with a particular gene cluster has not been yet established. In the present transcriptome study we show that veA is necessary for the expression of a larger number of genes. Twenty-eight out of the predicted 56 gene clusters include at least one gene that is differentially expressed depending on veA. One of the clusters under the influence of veA is cluster 39. Absence of veA results in a down-regulation of the five genes found within this cluster. Interestingly, our results indicate that the cluster is mainly expressed in sclerotia. Chemical analysis of sclerotial extracts revealed that cluster 39 is responsible for the production of aflavarin.