There and back again: historical perspective and future directions for Vaccinium breeding and research studies

The genus Vaccinium L. (Ericaceae) contains a wide diversity of culturally and economically important berry crop species. Consumer demand and scientific research in blueberry (Vaccinium spp.) and cranberry (Vaccinium macrocarpon) have increased worldwide over the crops' relatively short domestication history (~100 years). Other species, including bilberry (Vaccinium myrtillus), lingonberry (Vaccinium vitis-idaea), and ohelo berry (Vaccinium reticulatum) are largely still harvested from the wild but with crop improvement efforts underway. Here, we present a review article on these Vaccinium berry crops on topics that span taxonomy to genetics and genomics to breeding. We highlight the accomplishments made thus far for each of these crops, along their journey from the wild, and propose research areas and questions that will require investments by the community over the coming decades to guide future crop improvement efforts. New tools and resources are needed to underpin the development of superior cultivars that are not only more resilient to various environmental stresses and higher yielding, but also produce fruit that continue to meet a variety of consumer preferences, including fruit quality and health related trait

Physiological and transcriptomic responses in the seed coat of field-grown soybean (Glycine max L. Merr.) to abiotic stress

Abstract Background Understanding how intensification of abiotic stress due to global climate change affects crop yields is important for continued agricultural productivity. Coupling genomic technologies with physiological crop responses in a dynamic field environment is an effective approach to dissect the mechanisms underpinning crop responses to abiotic stress. Soybean (Glycine max L. Merr. cv. Pioneer 93B15) was grown in natural production environments with projected changes to environmental conditions predicted for the end of the century, including decreased precipitation, increased tropospheric ozone concentrations ([O3]), or increased temperature. Results All three environmental stresses significantly decreased leaf-level photosynthesis and stomatal conductance, leading to significant losses in seed yield. This was driven by a significant decrease in the number of pods per node for all abiotic stress treatments. To understand the underlying transcriptomic response involved in the yield response to environmental stress, RNA-Sequencing analysis was performed on the soybean seed coat, a tissue that plays an essential role in regulating carbon and nitrogen transport to developing seeds. Gene expression analysis revealed 49, 148 and 1,576 differentially expressed genes in the soybean seed coat in response to drought, elevated [O3] and elevated temperature, respectively. Conclusions Elevated [O3] and drought did not elicit substantive transcriptional changes in the soybean seed coat. However, this may be due to the timing of sampling and does not preclude impacts of those stresses on different tissues or different stages in seed coat development. Expression of genes involved in DNA replication and metabolic processes were enriched in the seed coat under high temperate stress, suggesting that the timing of events that are important for cell division and proper seed development were altered in a stressful growth environment

Transcriptome‐based identification and functional characterization of iridoid synthase involved in monotropein biosynthesis in blueberry

Abstract Blueberries (Vaccinium spp.) are well known for their nutritional quality, and recent work has shown that Vaccinium spp. also produce iridoids, which are specialized metabolites with potent health‐promoting benefits. The iridoid glycoside monotropein, which has anti‐inflammatory and antinociceptive activities, has been detected in several wild blueberry species but in only a few cultivated highbush blueberry cultivars. How monotropein is produced in blueberry and the genes involved in its biosynthesis remain to be elucidated. Using a monotropein‐positive (M+) and monotropein‐negative (M−) cultivar of blueberry, we employed transcriptomics and comparative genomics to identify candidate genes in the blueberry iridoid biosynthetic pathway. Orthology analysis was completed using de novo transcript assemblies for both the M+ and M− blueberry cultivars along with the known iridoid‐producing plant species Catharanthus roseus to identify putative genes involved in key steps in the early iridoid biosynthetic pathway. From the identified orthologs, we functionally characterized iridoid synthase (ISY), a key enzyme involved in formation of the iridoid scaffold, from both the M+ and M− cultivars. Detection of nepetalactol suggests that ISY from both the M+ and M− cultivars produce functional enzymes that catalyze the formation of iridoids. Transcript accumulation of the putative ISY gene did not correlate with monotropein production, suggesting other genes in the monotropein biosynthetic pathway may be more directly responsible for differential accumulation of the metabolite in blueberry. Mutual rank analysis revealed that ISY is co‐expressed with UDP‐glucuronosyltransferase, which encodes an enzyme downstream of the ISY step. Results from this study contribute new knowledge in our understanding of iridoid biosynthesis in blueberry and could lead to development of new cultivars with increased human health benefits

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

<div><p>Cultivated blueberry (<i>Vaccinium corymbosum</i>, <i>Vaccinium angustifolium</i>, <i>Vaccinium darrowii</i>, and <i>Vaccinium virgatum</i>) 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 <i>V</i>. <i>corymbosum</i>, <i>V</i>. <i>angustifolium</i> and <i>V</i>. <i>virgatum</i>; 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 <i>Vaccinium</i> 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.</p></div

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

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

Example chromatogram demonstrating the presence of monotropein in blueberry.

<p>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 (<i>m/z</i> 413.013; [M+Na]⁺) in positive mode.</p

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

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

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

<p>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 <i>Vaccinium</i> species. Error bars represent mean ± standard error (n = 1, samples analyzed in triplicate).</p

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

<p>Error bars represent mean ± standard error (n = 1 or 2).</p

Previously published research on iridoids in <i>Vaccinium</i> species and neotropical blueberries.

<p>Previously published research on iridoids in <i>Vaccinium</i> species and neotropical blueberries.</p