Floral Scent Composition and Fine-Scale Timing in Two Moth-Pollinated Hawaiian Schiedea (Caryophyllaceae)

Cloning, Expression and Functional Characterization of a Novel α-Humulene Synthase, Responsible for the Formation of Sesquiterpene in Agarwood Originating from Aquilaria malaccensis

This study describes the cloning, expression and functional characterization of α-humulene synthase, responsible for the formation of the key aromatic compound α-humulene in agarwood originating from Aquilaria malaccensis. The partial sesquiterpene synthase gene from the transcriptome data of A. malaccensis was utilized for full-length gene isolation via a 3' RACE PCR. The complete gene, denoted as AmDG2, has an open reading frame (ORF) of 1671 bp and encodes for a polypeptide of 556 amino acids. In silico analysis of the protein highlighted several conserved motifs typically found in terpene synthases such as Asp-rich substrate binding (DDxxD), metal-binding residues (NSE/DTE), and cytoplasmic ER retention (RxR) motifs at their respective sites. The AmDG2 was successfully expressed in the E. coli:pET-28a(+) expression vector whereby an expected band of about 64 kDa in size was detected in the SDS-PAGE gel. In vitro enzyme assay using substrate farnesyl pyrophosphate (FPP) revealed that AmDG2 gave rise to two sesquiterpenes: α-humulene (major) and β-caryophyllene (minor), affirming its identity as α-humulene synthase. On the other hand, protein modeling performed using AlphaFold2 suggested that AmDG2 consists entirely of α-helices with short connecting loops and turns. Meanwhile, molecular docking via AutoDock Vina (Version 1.5.7) predicted that Asp307 and Asp311 act as catalytic residues in the α-humulene synthase. To our knowledge, this is the first comprehensive report on the cloning, expression and functional characterization of α-humulene synthase from agarwood originating from A. malaccensis species. These findings reveal a deeper understanding of the structure and functional properties of the α-humulene synthase and could be utilized for metabolic engineering work in the future.

The Nighttime Fragrance of Guettarda scabra (Rubiaceae): Flower Scent and Its Implications for Moth Pollination

Floral scent is crucial for attracting pollinators, especially in plants that bloom at night. However, chemical profiles of flowers from nocturnal plants with varied floral morphs are poorly documented, limiting our understanding of their pollination ecology. We investigated the floral scent in Guettarda scabra (L.) Vent. (Rubiaceae), a night-blooming species with short- and long-styled floral morphs, found in the threatened pine rocklands in south Florida, US. By using dynamic headspace sampling and GC-MS analysis, we characterized the chemical profiles of the floral scent in both morphs. Neutral red staining was also employed to determine the specific floral regions responsible for scent emission in G. scabra. The results revealed that G. scabra's fragrance consists entirely of benzenoid and terpenoid compounds, with benzeneacetaldehyde and (E)-β-ocimene as dominant components. There were no differences in the chemical profiles between the long- and short-styled flowers. Staining assays indicated that the corolla lobes, anthers, and stigma were the primary sources of the scent. These findings indicate that G. scabra's floral scent is consistent with that of night-blooming plants pollinated by nocturnal hawkmoths, providing important insights into its chemical ecology and pollinator attraction. This study demonstrates how floral scent chemistry can validate predictions based on flower morphology in hawkmoth-pollinated plants.

NMπ 2.0: Software update to minimize the risk of false positives among determinants of reproductive success

In plant populations, parentage analysis helps understand factors shaping individual reproductive success. However, estimating reproductive success determinants based on parentage counts requires decoupling the effects of individual fecundity and propagule dispersal. The neighbourhood model implemented in the NMπ software provides a standard solution for this problem based on the fixed-effects regression-like approach. Nonetheless, it has been recently shown that the method is prone to false discoveries when important fecundity determinants are omitted. To account for the unexplained variance in fecundity, the Bayesian approach was developed based on the new model (the hierarchical neighbourhood model; HNM). Here, I present the NMπ software update that allows the HNM approach to be used in the framework of a friendly interface. More importantly, the HNM approach is now made available for both dispersed (seedlings) and nondispersed (seeds with known mothers) progeny data. The Bayesian approach, among others, selects significant fecundity determinants, estimates the proportion of variance in reproductive potential explained by selected determinants (R² ), and provides individual female and male fecundity values. Although the software was designed to handle microsatellite marker data, a solution is proposed for large sets of single nucleotide polymorphisms. The program can be run on Windows (using either a terminal or a graphical interface) as well as (using a terminal) on Linux, or macOS platforms. In any case, NMπ can utilize multicore processors to speed up the analysis. The updated package containing the code, the executable file, the user manual, and example data is available at https://www.ukw.edu.pl/pracownicy/plik/igor_chybicki/3694/.

Floral scent divergence across an elevational hybrid zone with varying pollinators

Divergence in floral traits attractive to different pollinators can promote reproductive isolation in related species. When isolation is incomplete, hybridization may occur, which offers the opportunity to explore mechanisms underlying reproductive isolation. Recent work suggests that divergence in floral scent may frequently contribute to reproductive barriers, although such divergence has seldom been examined in species with generalized pollination. Here, we used two closely related Penstemon species, P. newberryi and P. davidsonii, and their natural hybrids from an elevational gradient with pollinator communities that are predicted to vary in their reliance on floral scent (i.e., primarily hummingbirds at low elevation vs. bees at high elevation). The species vary in a suite of floral traits, but scent is uncharacterized. To address whether scent varies along elevation and potentially contributes to reproductive isolation, we genetically characterized individuals collected at field and identified whether they were parental species or hybrids. We then characterized scent amount and composition. Although the parental species had similar total emissions, some scent characteristics (i.e., scent composition, aromatic emission) diverged between them and may contribute to their isolation. However, the species emitted similar compound sets which could explain hybridization in the contact area. Hybrids were similar to the parents for most scent traits, suggesting that their floral scent would not provide a strong barrier to backcrossing. Our study suggests floral scent may be a trait contributing to species boundaries even in plants with generalized pollination, and reinforces the idea that evolutionary pollinator transitions may involve changes in multiple floral traits.

Genetic potential for changes in breeding systems: Predicted and observed trait changes during artificial selection for male and female allocation in a gynodioecious species

PREMISE

Evolution of separate sexes from hermaphroditism often proceeds through gynodioecy, but genetic constraints on this process are poorly understood. Genetic (co-)variances and between-sex genetic correlations were used to predict evolutionary responses of multiple reproductive traits in a sexually dimorphic gynodioecious species, and predictions were compared with observed responses to artificial selection.

METHODS

Schiedea (Caryophyllaceae) is an endemic Hawaiian lineage with hermaphroditic, gynodioecious, subdioecious, and dioecious species. We measured genetic parameters of Schiedea salicaria and used them to predict evolutionary responses of 18 traits in hermaphrodites and females in response to artificial selection for increased male (stamen) biomass in hermaphrodites or increased female (carpel, capsule) biomass in females. Observed responses over two generations were compared with predictions in replicate lines of treatments and controls.

RESULTS

In only two generations, both stamen biomass in hermaphrodites and female biomass in females responded markedly to direct selection, supporting a key assumption of models for evolution of dioecy. Other biomass traits, pollen and ovule numbers, and inflorescence characters important in wind pollination evolved indirectly in response to selection on sex allocation. Responses generally followed predictions from multivariate selection models, with some responses unexpectedly large due to increased genetic correlations as selection proceeded.

CONCLUSIONS

Results illustrate the power of artificial selection and utility of multivariate selection models incorporating sex differences. They further indicate that pollen and ovule numbers and inflorescence architecture could evolve in response to selection on biomass allocation to male versus female function, producing complex changes in plant phenotype as separate sexes evolve.

Population-specific responses of floral volatiles to abiotic factors in changing environments

PREMISE

Shifts in abiotic factors can affect many plant traits, including floral volatiles. This study examined the response of floral volatiles to water availability and whether phenotypic plasticity to water availability differs among populations. It also investigated genetic differentiation in floral volatiles, determined the effect of temperature on phenotypic plasticity to water availability, and assessed temporal variation in floral scent emission between day and evening, since pollinator visitation differs at those times.

METHODS

Rocky Mountain columbine plants (Aquilegia coerulea), started from seeds collected in three wild populations in Colorado, Utah, and Arizona, were grown under two water treatments in a greenhouse in Madison, Wisconsin, United States. One population was also grown under the two water treatments, at two temperatures. Air samples were collected from enclosed flowers using dynamic headspace methods and floral volatiles were identified and quantified by gas chromatography (GC) with mass spectrometry (MS).

RESULTS

Emission of three floral volatiles increased in the wetter environment, indicating phenotypic plasticity. The response of six floral volatiles to water availability differed among populations, suggesting genetic differentiation in phenotypic plasticity. Five floral volatiles varied among populations, and emission of most floral volatiles was greater during the day.

CONCLUSIONS

Phenotypic plasticity to water availability permits a quick response of floral volatiles in changing environments. The genetic differentiation in phenotypic plasticity suggests that phenotypic plasticity can evolve but complicates predictions of the effects of environmental changes on a plant and its pollinators.

Real-Time Visualization of Scent Accumulation Reveals the Frequency of Floral Scent Emissions

Flowers emit a bouquet of volatiles to attract pollinators or to protect flowers from pathogen and herbivore attacks. Most floral volatiles are synthesized in the cytoplasm of petals and released into the headspace at a specific time of day. Various floral scent sampling methods coupled with gas chromatography-mass spectrometry have been used to measure the quality and quantity of floral volatiles. However, little is known about the emission patterns of floral scents. In most cases, it is still unclear whether floral scents emit continuously or discontinuously. Here we measured the frequency with which lily flowers emit scents using optical interferometry. By analyzing the refractive index difference between volatile organic compounds and ambient air, we were able to visualize the accumulation of the volatile vapors. The frequency of volatile emission was calculated from the unique footprint of temporal power spectrum maps. Based on these real-time measurements, we found that lily flowers emit the volatile compounds discontinuously, with pulses observed around every 10-50 min.

Variation in floral volatiles across time, sexes, and populations of wind-pollinated Schiedea globosa

PREMISE

Floral scent is a key aspect of plant reproduction, but its intraspecific variation at multiple scales is poorly understood. Sexual dimorphism and temporal regulation of scent can be shaped by evolution, and interpopulation variation may be a bridge to species differences. We tested whether intraspecific chemical diversity in a wind-pollinated species where selection from biotic pollination is absent is associated with genetic divergence across the Hawaiian archipelago.

METHODS

Floral volatiles from females, males, and hermaphrodites of subdioecious Schiedea globosa grown in a common environment from 12 populations were sampled day and night and analyzed by gas chromatography-mass spectrometry. Variation among groups was analyzed by constrained ordination. We also examined the relationships of scent dissimilarity to geographic and genetic distance between populations.

RESULTS

Flowers increased total emissions at night through higher emissions of several ketones, oximes, and phenylacetaldehyde. Females emitted less total scent per flower at night but more of some aliphatic compounds than males, and males emitted more ketones and aldoximes. Scent differed among populations during day and night. Divergence in scent produced at night increased with geographic distance within 70-100 km and increased with genetic distance for males during the day and night, but not for females.

CONCLUSIONS

Schiedea globosa exhibits diel and sex-based variation in floral scent despite wind pollination and presumed loss of biotic pollination. In males, interpopulation scent differences are correlated with genetic differences, suggesting that scent evolved with dispersal within and across islands.

Analytical strategies for in-vivo evaluation of plant volatile emissions - A review

Biogenic volatile organic compounds (BVOCs) are metabolites emitted by living plants that have a fundamental ecological role since they influence atmospheric chemistry, plant communication and pollinator/herbivore behaviour, and human activities. Over the years, several strategies have been developed to isolate and identify them, and to take advantage of their activity. The main techniques used for in-vivo analyses include dynamic headspace (D-HS), static headspace (S-HS) and, more recently, direct contact (DC) methods in association with gas chromatography (GC) and mass spectrometry (MS). The aim of this review is to provide insight into the in-vivo characterisation of plant volatile emissions with a focus on sampling, analysis and possible applications. This review first provides a critical discussion of the challenges associated with conventional approaches and their limitations and advantages. Then, it describes a series of applications of in-vivo volatilomic studies to enhance how the information they provide impact on our knowledge of plant behaviour, including the effects of abiotic (damage, flooding, climate) and biotic (insect feeding) stress factors in relation to the plants.