Biology subjects

Hegeman, A. D.

Publications and source records attributed to Hegeman, A. D..

4 recordsLinked to original sources

bioRxiv2025

Biosynthesis of a major plant immunity hormone, salicylate, changed drastically during evolution of flowering plants

Salicylate (SA) is a major plant immunity hormone that activates immune responses against biotrophic pathogens. Between two known SA biosynthetic routes, the isochorismate synthase (ICS) and phenylalanine ammonia-lyase (PAL) pathways, which predominates in particular flowering plants has remained uncertain. We established a straightforward approach that directly quantifies the relative contributions of the ICS and PAL pathways and can also reveal an alternative, non-ICS/PAL route. In this approach, SA and shikimate (ShA), the precursor of SA in the ICS and PAL pathways, were metabolically labeled with [13C6]glucose in leaf tissue. We analyzed the LC-MS/MS data of the compounds using a metabolism-guided statistical model (the ICS-PAL model). This analysis allowed tracking of the origins of their ring and carboxyl carbons and, consequently, determination of the main SA biosynthetic routes. We surveyed SA biosynthetic routes in plants of the order Brassicales, other diverse eudicots, a monocot, magnoliids, and basal angiosperms. We found that the main SA biosynthetic routes changed at least twice during evolution of flowering plants: from a non-ICS/PAL pathway to the PAL pathway around the divergence time of monocots, and from the PAL pathway to the ICS pathway within Brassicales. Application of another metabolism-guided statistical model (the PKS-PAL model) to the SA data suggested that the non-ICS/PAL pathway involves a type III polyketide synthase (PKS). Typically, once a biosynthetic pathway is established for an important molecule, it is conserved in the subsequent lineage. SA biosynthesis in flowering plants took an unusual evolutionary path in which the pathways changed drastically multiple times. This unconventional evolutionary mechanism was employed for a major immunity hormone, likely due to rapid evolution of biotic environments, such as pathogens and insects that attack plants.

plant biology↗

bioRxiv2023

Methods for assessing bee foraging preferences: a short review and a new automated apparatus

Bees are essential pollinators for many plant species, but multiple threats exist to both managed and wild bee populations. Their innate foraging behaviors and food preferences are subjects of intense research since bee nutrition is essential for maintaining hive and colony health. Multiple approaches have been developed to assess bee foraging behavior and associated preferences, but they are often labor-intensive and provide data on a limited number of parameters. In this manuscript, we provide a short review of these methods and present the design, build, and implementation of a new, inexpensive, and automated feeding apparatus capable of recording: (1) number of visits, (2) total food consumed, (3) photos and videos of bee behavior while inside of the feeder, and (4) environmental conditions. The efficacy of this apparatus is demonstrated through preference tests with artificial nectars, while also acknowledging the relative strengths and limitations of this approach.

animal behavior and cognition↗

bioRxiv2022

Post-secretory synthesis of a natural analog of iron-gall ink in the black nectar of Melianthus spp.

The black nectar of Melianthus flowers is thought to serve as a visual attractant to pollinators, but the chemical identity and synthesis of the black pigment are unknown. Here we report that the black nectar contains a natural analog of iron-gall ink, which humans have used since medieval times. Specifically, dark black nectar at anthesis contains high levels of ellagic acid and iron; synthetic solutions of ellagic acid and iron(III) recapitulate the black color of the nectar. Conversely, lightly colored nectars before and after anthesis contain significantly lower levels of ellagic acid and iron, but higher levels of gallic acid. We then explored the possibility of post-secretory synthesis of ellagic acid from gallic acid. Indeed, Melianthus nectar contains a peroxidase that oxidizes gallic acid to form ellagic acid. Reactions containing the nectar peroxidase, gallic acid, hydrogen peroxide, and iron can fully recreate the black color of the nectar. Visual modeling indicates that the black color is both visible and conspicuous to birds within the context of the flower. In summary, the black nectar of Melianthus is derived from an ellagic acid-Fe complex analogous to iron-gall ink and is likely involved in the attraction of passerine bird pollinators.

plant biology↗

bioRxiv2021

Convergent evolution of a novel blood-red nectar pigment in vertebrate-pollinated flowers

Nesocodon mauritianus (Campanulaceae) produces a blood-red nectar that has been proposed to serve as a visual attractant for pollinator visitation. Here we show that the nectars red color is derived from a novel alkaloid termed nesocodin. The first nectar produced is acidic and pale yellow in color, but slowly becomes alkaline before taking on its characteristic red color. Three enzymes secreted into the nectar are either necessary or sufficient for pigment production, including (1) a carbonic anhydrase that creates an alkaline environment, (2) an aryl alcohol oxidase that generates sinapaldehyde, a pigment precursor, and (3) a ferritin-like catalase that protects nesocodin from degradation by hydrogen peroxide. Our findings demonstrate how these three enzymatic activities allow for the condensation of sinapaldehyde and proline to form a novel pigment with a stable imine bond, which in turn is attractive to Phelsuma geckos, the presumed pollinators of Nesocodon. We also identify nesocodin in the red nectar of the distantly related Jaltomata herrerae and provide evidence for convergent evolution of this trait. While the overall enzymatic activities required for red pigment formation in both Nesocodon and J. herrerae nectars are identical, the associated genes encoding the enzymes are not orthologous and, in the case of the aryl alcohol oxidase, even belong to different protein families. This work cumulatively identifies a novel, convergently evolved trait in two vertebrate-pollinated species, suggesting the red pigment is selectively favored and that only a limited number of compounds are likely to underlie this adaptation. SignificanceNearly 90% of flowering plants produce nectar to attract pollinators. Beyond sugars, many types of nectar solutes play important ecological roles; however, the molecular basis for the diversity of nectar composition across species is less explored. One rare trait among flowering plants is the production of colored nectar, which may function to attract and guide prospective pollinators. Our findings indicate convergent evolution of a red-colored nectar across two distantly related plant species. Behavioral data show that the red pigment attracts diurnal geckos, a presumed pollinator of one of these plants. These findings join a growing list of examples of distinct biochemical and molecular mechanisms underlying evolutionary convergence, and provide a fascinating system for testing how interactions across species drive the evolution of novel pigments in an understudied context.

evolutionary biology↗