Agriculture researchers discover toxic enzyme

RIKEN Center for Sustainable Resource Sciences (CSRS) researchers have found an enzyme critical to the synthesis of tenuazonic acid (TeA), which is a fungi-produced toxin that affects crops including fruits, vegetables and rice.

These fungi-produced toxic compounds, also referred to as mycotoxins, are not directly involved in the growth of plants. Instead, secondary metabolites colonize and spoil crops, resulting in an economic burden for farmers.

“Now that we know the gene responsible for biosynthesis of this harmful toxin,” co-lead author of the study Takayuki Motoyama said. “After further testing, we might be able to devise a way to regulate its expression and prevent destruction of important crops.”

The researchers were able to produce TeA in both a research lab and by culturing wild-type M. oryzae with 1 percent dimethylsulphoxide, perhaps as a response to the unfavorable environment. They determined the gene that produced TeA biosynthesis and renamed it TeA synthetase 1 (TAS1). TAS1 was found to be a hybrid enzyme containing an NRPS region followed by a PKS region. The researchers determined that TAS1 synthesizes from isoleucine and acetoacetyl-coenzyme A.

“This was very surprising," Motoyama said. “It was assumed because of TeA’s structure that it would be synthesized by a PKS-NRPS hybrid enzyme. In fact, the order of these regions was totally reversed.”

Although TeA synthesis is bad for crops, it also has potential benefits with anti-tumor, antibacterial and antiviral properties.

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