Elucidation of biosynthetic pathway of a plant hormone abscisic acid in phytopathogenic fungi

ABSTRACT

Abscisic acid (ABA) is one of the plant hormones that regulates physiological functions in various organisms, including plants, sponges, and humans. The biosynthetic machinery in plants is firmly established, while that in fungi is still unclear. Here, we elucidated the functions of the four biosynthetic genes, bcABA1-bcABA4, found in Botrytis cinerea by performing biotransformation experiments and in vitro enzymatic reactions with putative biosynthetic intermediates. The first-committed step is the cyclization of farnesyl diphosphate to give α-ionylideneethane catalyzed by a novel sesquiterpene synthase, BcABA3, which exhibits low amino acid sequence identities with sesquiterpene synthases. Subsequently, two cytochrome P450s, BcABA1 and BcABA2, mediate oxidative modifications of the cyclized product to afford 1ʹ,4ʹ-trans-dihydroxy-α-ionylideneacetic acid, which undergoes alcohol oxidation to furnish ABA. Our results demonstrated that production of ABA does not depend on the nucleotide sequence of bcABA genes. The present study set the stage to investigate the role of ABA in infections.

Graphical abstract

Biosynthetic pathway of a plant hormone abscisic acid produced by phytopathogenic fungi was elucidated through biotransformation experiments.

KEYWORDS:

• Abscisic acid
• plant hormone
• oxidative modifications
• Aspergillus oryzae
• phytopathogenic fungi

Author contribution

J.T., T.K., A.M., and H.O. designed research; J.T., and T.K. performed research; A.M., J.T., T.K., T.O., C.L., A.M., and H.O. analyzed data; and A.M. and H.O. wrote the paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was financially supported by Japan Society for the Promotion of Science Grants [JP15H01835, JP16H03277, and JP16H06446]; Noda Institute for Scientific Research [000].