Differential iridoid production as revealed by a diversity panel of 84 cultivated and wild blueberry species

Abstract

Cultivated blueberry (Vaccinium corymbosum, Vaccinium angustifolium, Vaccinium darrowii, and Vaccinium virgatum) is an economically important fruit crop native to North America and a member of the Ericaceae family. Several species in the Ericaceae family including cranberry, lignonberry, bilberry, and neotropical blueberry species have been shown to produce iridoids, a class of pharmacologically important compounds present in over 15 plant families demonstrated to have a wide range of biological activities in humans including anti-cancer, anti-bacterial, and anti-inflammatory. While the antioxidant capacity of cultivated blueberry has been well studied, surveys of iridoid production in blueberry have been restricted to fruit of a very limited number of accessions of V. corymbosum, V. angustifolium and V. virgatum; none of these analyses have detected iridoids. To provide a broader survey of iridoid biosynthesis in cultivated blueberry, we constructed a panel of 84 accessions representing a wide range of cultivated market classes, as well as wild blueberry species, and surveyed these for the presence of iridoids. We identified the iridoid glycoside monotropein in fruits and leaves of all 13 wild Vaccinium species, yet only five of the 71 cultivars. Monotropein positive cultivars all had recent introgressions from wild species, suggesting that iridoid production can be targeted through breeding efforts that incorporate wild germplasm. A series of diverse developmental tissues was also surveyed in the diversity panel, demonstrating a wide range in iridoid content across tissues. Taken together, this data provides the foundation to dissect the molecular and genetic basis of iridoid production in blueberry.

Fig 1. Example chromatogram demonstrating the presence of monotropein in blueberry.

Chemical structure of iridoid glycoside monotropein (A). Multiple reaction monitoring (MRM) chromatograms (413.013 > 233.094) of analytical standard monotropein (B), alongside representative blueberry cultivar Summit (C). Monotropein was detected as a sodium adduct (m/z 413.013; [M+Na]⁺) in positive mode.

Fig 2. Quantification of the glycoside iridoid monotropein in fruit tissue for the 84-member blueberry diversity panel.

A) Quantification of monotropein for all 71 cultivated blueberry varieties sampled in 2015. Values of zero represent cultivars where monotropein could not be detected under current conditions, i.e. below the limit of detection. B) Quantification of monotoropein for all 13 wild Vaccinium species. Error bars represent mean ± standard error (n = 1, samples analyzed in triplicate).

Fig 3. Quantification of the iridoid glycoside monotropein in ripe fruit and young leave tissue of five blueberry cultivars.

Error bars represent the mean ± standard error (n = 1–3).

Fig 4. Pedigree diagram of select monotropein-positive and negative cultivars in blueberry diversity panel.

A) Ornablue, B) Ozarkblue (Summit is a full-sibling and thus has the same pedigree), and C) Cara’s Choice. Ozarkblue pedigree information adapted from [30].

Fig 5. Quantification of the iridoid glycoside monotropein in a tissue series for six cultivars from the blueberry diversity panel.

Error bars represent mean ± standard error (n = 1 or 2).