Abstract
Aspergillus flavus and Aspergillus parasiticus are important pathogens of cotton, corn, peanuts and other oil-seed crops, producing toxins both in the field and during storage. We have designed three siRNA sequences (Nor-Ia, Nor-Ib, Nor-Ic) to target the mRNA sequence of the aflD gene to examine the potential for using RNA silencing technology to control aflatoxin production. Thus, the effect of siRNAs targeting of two key genes in the aflatoxin biosynthetic pathway, aflD (structural) and aflR (regulatory gene) and on aflatoxin B1 (AFB1), and aflatoxin G1 (AFG1) production was examined. The study showed that Nor-Ib gave a significant decrease in aflD mRNA, aflR mRNA abundance, and AFB1 production (98, 97 and 97% when compared to the controls) in A. flavus NRRL3357, respectively. Reduction in aflD and aflR mRNA abundance and AFB1 production increased with concentration of siRNA tested. There was a significant inhibition in aflD and AFB1 production by A. flavus EGP9 and AFG1 production by A. parasiticus NRRL 13005. However, there was no significant decrease in AFG1 production by A. parasiticus SSWT 2999. Changes in AFB1 production in relation to mRNA levels of aflD showed a good correlation (R = 0.88; P = 0.00001); changes in aflR mRNA level in relation to mRNA level of aflD also showed good correlation (R = 0.82; P = 0.0001). The correlations between changes in aflR and aflD gene expression suggests a strong relationship between these structural and regulatory genes, and that aflD could be used as a target gene to develop efficient means for aflatoxin control using RNA silencing technology.
Highlights
Aflatoxins are secondary metabolites produced by Aspergillus flavus and A. parasiticus that occur in nuts and cereal crops
The objective of this study was to determine the potential of siRNA for silencing the target gene and phenotypic aflatoxin control in strains of A. flavus and A. parasiticus
Treatment with the control-siRNA had no significant effect on aflatoxin B1 (AFB1) production or aflD/aflR messenger RNA (mRNA)
Summary
Aflatoxins are secondary metabolites produced by Aspergillus flavus and A. parasiticus that occur in nuts and cereal crops. These compounds have a high acute toxicity, as well as immunosuppressive, mutagenic, teratogenic, and carcinogenic activities and are classified as group 1 carcinogens by the International Agency for Research on Cancer [1]. Controlling aflatoxin production is of critical importance. Traditional control methods including cultural practices such as pesticides and the development of resistant cultivars, pest resistance have been used. These have not always been successful in maize and in groundnuts. There is interest in exploring alternative means to control or reduce aflatoxin production
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