Identification of HydroxypyrazineO-Methyltransferase Genes inCoffea arabica: A Potential Source of Methoxypyrazines That Cause Potato Taste Defect

Abstract

The goal of this study is to identify Coffea arabica O-methyltransferase (OMT) genes involved in the biosynthesis of methoxypyrazines. High levels of 2-isopropyl-3-methoxypyrazine (IPMP) and 2-isobutyl-3-methoxypyrazine (IBMP) in coffee beans are associated with the potato taste defect (PTD). Among the 34 putative O-methyltransferase genes identified in the published genome of C. canephora, three genes are highly homologous to known hydroxypyrazine OMT genes. Genes of interest were amplified and sequenced from genomic DNA of single C. arabica beans grown in eight different locations, including regions with endemic PTD. Although C. arabica OMT target sequences were almost identical regardless of source location, individual beans shared numerous polymorphisms in each of the target genes. Two of the predicted C. arabica OMT enzymes were successfully expressed in Escherichia coli and purified, and one enzyme shows slow yet measurable turnover of both 3-isobutyl-2-hydroxypyrazine (IBHP) and 3-isopropyl-2- hydroxypyrazine (IPHP), supporting a possible role of the coffee plant in PTD.

Analytical Determination of the Severity of Potato Taste Defect in Roasted East African Arabica Coffee

“…35 Furthermore, it was hypothesized that bug predation along with other environmental stresses may upregulate OMT expression in the coffee plant, contributing to elevated IBMP and IPMP levels in the coffee beans. 14 However, the concentrations of IBMP observed herein and previously 7 and lack of correlation to PTD suggest that other environmental stressors may influence the expression of this OMT in all coffee plants. Even though IBMP may not aid in determining if roasted coffee beans have been affected by PTD, this analyte shows high variability based on geographical origin.…”

“…12,13 Another line of evidence suggests that antestia predation triggers an increase in O-methyltransferase (OMT) expression, which is responsible for converting precursor hydroxypyrazines into methoxypyrazines such as IPMP and 2-isobutyl-3methoxypyrazine (IBMP). 14 Both mechanisms can explain the occurrence of PTD in coffee beans with and without visible insect damage. 7 Alterations to the sensory properties of coffee due to the presence of defects have been observed in a coffee sample's chemical profile, especially in the vapor headspace.…”

G × E interactions on yield and quality in Coffea arabica: new F1 hybrids outperform American cultivars

“…Few studies concern volatile compounds in green coffee beans. Some volatiles compounds, in green beans as well as in roasted beans, are identified as possible markers of high quality (Toledo et al 2016;Casas et al 2017) whereas others are related with defects (Toci and Farah 2014;Frato 2019).…”

“…The variance between genotypes was lower than the variance between environments except for D-limonene, 2-Methyl-2-buten-1-ol, 2-isobutyl-3-methoxypyrazine (IBMP), 3-Methylbutanoic acid and 3-Methylfuran. D-limonene (clean smell, characteristic of citrus fruits) and 2-Methyl-2-buten-1-ol (fruity, green lavender) are associated with positive sensory notes (Del Terra et al 2013), whereas 2-isobutyl-3-methoxypyrazine (IBMP) is associated with 'potato taste defect' (Frato 2019). Starmaya and Centroamericano-H1 contain more D-limonene and are significantly different from Caturra and Mundo Maya-H16.…”

Significance and Transformation of 3-Alkyl-2-Methoxypyrazines Through Grapes to Wine: Olfactory Properties, Metabolism, Biochemical Regulation, and the HP–MP Cycle

“…Thus, VvOMT3 is proposed as the major gene involved in IBMP biosynthesis in grapevines [30,65]. In latest years, OMT genes in Coffea arabica [66] and Nicotiana benthamiana [32] were also found by blast against VvOMTs.…”