Identification of a methyltransferase catalyzing the final step of methyl anthranilate synthesis in cultivated strawberry

Authors: PILLETT, JEREMY - University Of Florida; CHAMBERS, ALAN - University Of Florida; BARBEY, CHRISTOPHER - University Of Florida; BOA, ZHILONG - University Of Florida; Plotto, Anne; Bai, Jinhe; SCHWIETERMAN, MICHAEL - University Of Florida; JOHNSON, TIMOTHY - University Of Florida; HARRISON, BENJAMIN - University Of Florida; WHITAKER, VANCE - University Of Florida; COLQUHOUN, THOMAS - University Of Florida; FOLTA, KEVIN - University Of Florida

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2017
Publication Date: 8/31/2017
Citation: Pillett, J., Chambers, A.H., Barbey, C., Boa, Z., Plotto, A., Bai, J., Schwieterman, M., Johnson, T., Harrison, B., Whitaker, V., Colquhoun, T., Folta, K. 2017. Identification of a methyltransferase catalyzing the final step of methyl anthranilate synthesis in cultivated strawberry. Biomed Central (BMC) Plant Biology. 17:147-159. https://doi.10.1186/s12870-017-1088-1.
DOI: https://doi.org/10.1186/s12870-017-1088-1

Interpretive Summary: Strawberry is an attractive fruit but over the years, breeding plants for commercial production has emphasized size, shipping capabilities and reduced flavor diversity. Methyl anthranilate is a volatile flavor compound found in old European wild strawberry cultivars, and has recently received attention from breeders as a compound that could increase strawberry flavor. The present manuscript reports on a key enzyme in the production of methyl anthranilate in strawberry fruit, anthranilic acid methyl transferase, and its genetic inheritability. The gene and its associated molecular maker were identified. This information may be directly used by breeder to select seedlings that have the potential of producing flavorful fruit.

Technical Abstract: Methyl anthranilate (MA) contributes an attractive fruity note to the complex flavor and aroma of strawberry (Fragaria spp.), yet it is rarely found in modern cultivars. The genetic basis for its biosynthesis has not been elucidated. Understanding the specific genes required for its synthesis could hasten the development of gene/allele-specific markers to speed breeding efforts of flavorful strawberries. Ripe fruits from individuals in an F1 population resulting from a cross between a MA producer and a non-producer were examined using a bulk-segregant transcriptome approach. MA producer and non-producer transcriptomes were compared, revealing five candidate transcripts that strictly co-segregated with MA production. One candidate, ANTHRANILIC ACID METHYL TRANSFERASE (FanAAMT) encodes an annotated methyltransferase. MA levels are lower when this transcript is suppressed with RNAi, and bacterial cultures expressing the protein produced MA in the presence of anthranilic acid. MA could be produced via carboxymethylation of exogenous anthranilic acid from fruit protein extracts incubated with ado-Met, but only in genotypes containing the FanAAMT transcript. A DNA-based molecular marker was developed that segregates with the MA-producing gene variant. These analyses indicate that the methyltransferase mediates the ultimate step of MA production in cultivated strawberry. Identification of this gene and its associated molecular marker may hasten breeding efforts to introduce this important volatile into modern cultivars.