Red milkweed beetle genome offers insight into plant-insect interactions

Genome of host-specialist red milkweed beetle compared to generalist relative

University of Arkansas System Division of Agriculture

 

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A mating pair of red milkweed beetles pictured in the spring of 2024 on the University of Arkansas campus in Fayetteville.

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Credit: U of A System Division of Agriculture photo by Rich Adams

FAYETTEVILLE, Ark. — Studying the secrets of how the common red milkweed beetle can safely feed on a toxic plant helps illuminate the ecological, evolutionary and economic impact of insect-plant interactions from a genomic perspective.

Although the relationship between the red milkweed beetle and milkweed plants has been studied for nearly 150 years, an Arkansas Agricultural Experiment Station scientist joined colleagues at the University of Memphis and the University of Wisconsin Oshkosh to do what no one else has done — curate the beetle’s genome and its arsenal of genes related to plant-feeding and other biological traits.

With support from the National Science Foundation, they sequenced and assembled the entire genome of the host-specialist milkweed beetle (Tetraopes tetrophthalmus). They then compared aspects of genome biology to a relative, the host-generalist Asian longhorned beetle (Anoplophora glabripennis), which is an invasive exotic species that feeds on a variety of trees important to forestry.

Their study, “Functional and evolutionary insights into chemosensation and specialized herbivory from the genome of the red milkweed beetle,” was published in the Journal of Heredity by the American Genetic Association this summer.

“From a biological standpoint, there is a lot of correspondence that suggests that longstanding interactions between milkweed beetles and their toxic milkweed hosts should influence the biology of both interacting partners,” said Rich Adams, a lead author of the study. “But, to date, no one had assembled a milkweed beetle genome, which opens the door for targeting a lot of interesting questions at the interface between insect and plant.”

Adams is an assistant professor of agricultural statistics in the department of entomology and plant pathology for the University of Arkansas System Division of Agriculture. He is also a member of the Center for Agricultural Data Analytics, a new initiative of the experiment station, and he teaches statistics courses in the Dale Bumpers College of Agricultural, Food and Life Sciences.

Scientific development

Milkweeds and milkweed beetles (genus Tetraopes) have been studied as valuable models for over a century of research into ecology, evolution, developmental biology, biochemistry of toxins and more, Adams said. They are also providing an interesting and compelling case of co-divergence patterns between insect and plant — meaning the plants and insects share similarities in the timing of co-evolution across their histories of interaction, Adams explained.

The research team showed that the red milkweed beetle has an apparent expansion of genes from the ABC transport family, which may help them feed on milkweeds and sequester its toxins inside beetle tissues. Milkweeds are renowned for their toxic latex cocktails, which affect the balance of sodium, calcium and potassium that keeps heart cells pumping. Adams said this genome provides insights into the genes the beetle has evolved to safely interact with its toxic milkweed hosts.

“Milkweeds produce a particularly nasty type of toxin called cardiac glycosides alongside other types of toxins that come with it,” Adams said. “For many insects that eat it, the toxin will block their sodium-potassium pumps. But this beetle developed a way to not only resist the toxin, but also sequester it, hold on to it, to keep the beetles themselves safe from would-be predators.”

The study also pinpointed differences in genes responsible for smell, taste and metabolic enzymes that degrade the plant cell well. Adams said it provides a new vantage point for exploring the ecology and evolution of specialized plant-feeding in longhorned beetles, and other plant-eating beetles.

Applications in agriculture, human health

These findings may help us understand and identify the genetic factors that shape agricultural and forestry pests and allow them to successfully feed on plants, as well as evade control efforts. Most animals that can digest woody plant material depend on microbes in their gut to break down plant cell walls; however, many plant-eating beetles do not.

Adams said many plant-feeding beetles, including longhorn beetles, acquired the ability to break down plant cell walls through horizontal gene transfers from microbes. By looking at the diversity of proteins encoded within beetle genomes, he said scientists can learn about the genomic basis of beetle biology, evolution and diversity, as well as their propensity for interactions with plants.

“Nature has made an incredible diversity of genes and genomes already out there that we have not yet deciphered,” Adams said. “Understanding this diversity holds great promise for informing agriculture, forestry and human health. Herbivorous beetles would have a difficult time feeding on plants without their metabolic enzymes, because they can’t eat effectively without them.”

In addition to studying the genomic DNA of the milkweed beetle, the team collected RNA from male and female red milkweed beetle antennae to learn more about how they seek out mates and food through chemosensation.

“Learning more about chemosensory biology — how an organism senses its environment, like sensing a host plant or reproductive partner — has broad relevance for understanding insect-plant interactions, which is intensively relevant to agriculture and forestry,” Adams said.

The RNA profile provided the first transcriptomic resource for Tetraopes. A transcriptome contains a range of genes that are transcribed into RNA molecules an organism expresses in a tissue or set of cells.

The DNA provides a gene sequence, the RNA offers “a better resolution of the gene and its expression, including how often the gene is getting made,” Adams explained.

Co-authors of the study included Terrence Sylvester (also a lead author) and Rongrong Shen, postdoctoral researchers at the University of Memphis with Duane D. McKenna, William Hill Professor in the department of biological sciences and director of the Center for Biodiversity; Matthew A. Price, formerly with the University of Wisconsin Oshkosh and now with the University of Hawaii at Manoa; and Robert F. Mitchell, formerly at the University of Wisconsin Oshkosh and now associate professor in the department of entomology at Pennsylvania State University.

The study was funded by National Science Foundation grants DEB-1355169 and DEB-2110053.

To learn more about the Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website. Follow us on X at @ArkAgResearch, subscribe to the Food, Farms and Forests podcast and sign up for our monthly newsletter, the Arkansas Agricultural Research Report. To learn more about the Division of Agriculture, visit uada.edu. Follow us on X at @AgInArk. To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit uaex.uada.edu.

About the Division of Agriculture

The University of Arkansas System Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system.

The Division of Agriculture is one of 20 entities within the University of Arkansas System. It has offices in all 75 counties in Arkansas and faculty on five system campuses.

The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.

 

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Journal

Journal of Heredity

DOI

10.1093/jhered/esae049 

Method of Research

Data/statistical analysis

Subject of Research

Animal tissue samples

Article Title

Functional and evolutionary insights into chemosensation and specialized herbivory from the genome of the red milkweed beetle, Tetraopes tetrophthalmus (Cerambycidae: Lamiinae)

Symbiotic bacterium Rickettsia affects the reproduction of a predatory insect, an effective biological control agent for agricultural pests

Peer-Reviewed Publication

National Agriculture and Food Research Organization

 

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The predatory mirid bug, Nesidiocoris tenuis, which preys on agricultural pests, is used as a biological control agent.

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Credit: National Agriculture and Food Research Organization (NARO)

Many insects are naturally infected with symbiotic bacteria, which are typically transmitted vertically from mother to offspring but are not transmitted horizontally. Understanding the effects of these symbionts is important in terms of insect pest management as they can significantly affect the biology and reproduction of insects. The predatory mirid bug, Nesidiocoris tenuis, which preys on agricultural pests such as whiteflies and thrips, is an important biological control agent. Although the symbiotic bacterium Rickettsia is often found in N. tenuis, its effects on the host have not been clarified.

A research team led by NARO and the University of Miyazaki has revealed that Rickettsia induces strong cytoplasmic incompatibility (CI) in N. tenuis. CI is a phenomenon where eggs laid by uninfected females fail to hatch when mated with infected males. In this study, mating experiments using Rickettsia-infected insects and antibiotic-treated uninfected insects demonstrated that eggs did not hatch, specifically in the combination of CI. This study newly adds Rickettsia to the list of CI-inducing symbiotic bacteria.

The genome analysis revealed that the Rickettsia strain in N. tenuis is closely related to the Bellii group, a group of symbiotic Rickettsia commonly found in insects. Notably, on the plasmids of this Rickettsia strain, there existed homologs of the CI factor gene (cif gene), which is known as the causal gene of CI in Wolbachia, another symbiotic bacterium known to induce CI. This suggests that the ability to induce CI may have been acquired through horizontal gene transfer between Wolbachia and Rickettsia, providing insights into the evolution of symbiont-induced reproductive manipulation in insects.

This discovery has significant implications for biological control which involves the reproduction of predatory insects that are used for pest management. If predatory insects do not reproduce as expected, CI could be the cause. Therefore, managing the infection status of symbiotic bacteria in the predatory insects could contribute to effective pest management in agriculture.

The research team highlighted the importance of assessing the frequency of CI in wild populations of N. tenuis. They also noted, “The wide distribution of N. tenuis and related species across Europe, Asia, and other regions offers potential for better use of predatory insects in agriculture and to explore the evolutionary origins of CI.”

Future research will focus on the mechanism of Rickettsia-induced CI, which is important for the effective management of N. tenuis as a biological control agent, as well as for a better understanding of host manipulation by symbiotic bacteria.

The mating experiment (IMAGE)

National Agriculture and Food Research Organization

Mating experiments were conducted with insects infected with Rickettsia and those cured of Rickettsia infection by antibiotic treatment. Among the four possible mating combinations, only the pairing of uninfected females and infected males resulted in 0% egg hatch rate.

Cytoplasmic incompatibility (CI) is a phenomenon where the offspring of insect species fail to develop properly when uninfected females mate with males infected with specific symbiotic bacteria.

Credit

National Agriculture and Food Research Organization (NARO)

About National Agriculture and Food Research Organization (NARO)
NARO is the core institute in Japan for conducting research and development in a wide range of fields, from basic to applied, for the development of agriculture and food industries.
For more information, visit https://www.naro.go.jp/english/index.html.
 

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Journal

Proceedings of the Royal Society B Biological Sciences

DOI

10.1098/rspb.2024.0680 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Rickettsia induces strong cytoplasmic incompatibility in a predatory insect

European forest plants are migrating westwards, nitrogen main cause

German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig

 

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The common wood sorrel (Oxalis acetosella) migrates westwards at a speed of around 5 kilometres per year and northwards at around 0.1 kilometres per year. The main driver is nitrogen deposition

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Credit: Petr Harant

New research reveals nitrogen pollution, and to a lesser extent climate change, unexpectedly as the key driver behind surprising westward shifts in the distribution of plants.

A recent study has uncovered that many European forest plant species are moving towards the west due to high nitrogen deposition levels, defying the common belief that climate change is the primary cause of species moving northward. This finding reshapes our understanding of how environmental factors, and in particular nitrogen pollution, influence biodiversity.

While it is widely assumed that rising temperatures are pushing many species toward cooler, northern areas, this research shows that westward movements are 2.6 times more likely than northward shifts. The primary driver? High levels of nitrogen deposition from atmospheric pollution, which allows a rapid spread of nitrogen-tolerating plant species from mainly Eastern Europe. The establishment of these highly competitive species in areas with high nitrogen deposition rates often comes at the expense of the more specialized plant species.

The results highlight that future biodiversity patterns are driven by complex interactions among multiple environmental changes, and not due to the exclusive effects of climate change alone. Understanding these complex interactions is critical for land managers and policymakers to protect biodiversity and ecosystem functioning.

Key findings:

• European forest plants shift their distributions at an average velocity of 3.56 kilometer per year.
• 39% of the plant species shift westward. Northward shifts are only observed for 15% of the species.
• Nitrogen pollution rather than climate change is surprisingly the main factor behind westward distribution shifts in European forest plants.
• The study analyzed the shifts in the distribution area of 266 forest plant species across Europe over several decades, with the first measurements being taken in the year 1933 at some locations.
• Several of Europe’s most emblematic forests were included in this study, such as the primeval forest Białowieża in Poland.

This research was financed inter alia by the Deutsche Forschungsgemeinschaft (DFG; FZT-118). It is a product of the sDiv working group sREplot. iDiv’s synthesis centre sDiv supports working group meetings where international scientists work together on scientific issues.

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Journal

Science

DOI

10.1126/science.ado0878 

Article Title

Unexpected westward range shifts in European forest plants links to nitrogen deposition

Article Publication Date

11-Oct-2024

Nitrogen deposition has shifted European forest plant ranges westward over decades

Summary author: Walter Beckwith

American Association for the Advancement of Science (AAAS)

Researchers have documented a shift in plant species ranges toward the poles or higher latitudes in the face of climate warming, but Pieter Sanczuk and colleagues now reveal another unexpected pattern of range shift. For decades, understory plants in European temperate forests have been on the move westward, spurred by differences in nitrogen deposition rates. Westward species distribution shifts were 2.6 times more likely than northward ones, according to the researchers, who also noted that forest canopy changes played a role in this shift as well. The findings suggest that factors beyond climate change, such as atmospheric pollution, are also an important part of redistributing biodiversity. Sanczuk et al. reviewed plant community data collected for 266 understory plant species from surveys between 1933 and 1994 and paired those data with resurvey information collected between 1987 and 2017. They found a trend of species ranges moving west over multiple decades that was connected to atmospheric nitrogen deposition rates. As generalist species shifted to take advantage of high-nitrogen areas, species that had experienced lower nitrogen depositions rates across their distributions initially had faster westward shifts. Colonization along the east-west axis was more closely related to nitrogen and sulfur deposition rates than measures of climate change such as temperature and precipitation.

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Journal

Science

DOI

10.1126/science.ado0878 

Article Title

Unexpected westward range shifts in European forest plants links to nitrogen deposition

Article Publication Date

11-Oct-2024

Seed dispersal “crisis” may impact plant species’ future in Europe

Summary author: Becky Ham

American Association for the Advancement of Science (AAAS)

Europe is facing a seed dispersal “crisis,” due to extinction threats and population changes among the animals that do the seed dispersing, according to a new synthesis by Sara Beatriz Mendes and colleagues. Their literature review of animal and plant dispersal pairs helped them reconstruct the first European-wide seed dispersal network. Seed dispersal by animals is a critical part of maintaining healthy ecosystems, especially in fragmented environments like those found throughout Europe. Lack of seed dispersal to connect populations could prevent declining plant populations from recovering. Researchers have thought that the loss of animal species in the region might impact this important process, but little is known about how these disperser-plant pairs are disrupted by species loss. Beatriz Mendes et al. found that one-third of these crucial interactions are of high concern, meaning that the species participating in them are listed as near threatened, threatened, or with declining populations by the IUCN Red List. They further note that 30% of plant species have most of their dispersers in the high concern category. Each animal species dispersed on average 13 plant species, while each plant species had on average nine dispersers. While the researchers acknowledge that there are significant gaps in disperser relationship data, they suggest their findings could be used to target conservation efforts to preserve high-concern disperser relationships.

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Journal

Science

DOI

10.1126/science.ado1464 

Article Title

Evidence of a European seed dispersal crisis

Article Publication Date

11-Oct-2024

 

Discovered by drones: World-first method reveals new plant species in endemic Hawaiian genus Schiedea

Pensoft Publishers

 

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Drone collection of plant.

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Credit: Ben Nyberg, National Tropical Botanical Garden and Outreach Robotics

Schiedea waiahuluensis, a newly discovered species from Hawaii in the carnation family, is likely the first plant to be identified and collected using drone technology.

Researchers used drone photography to spot the unknown species growing on steep, inaccessible cliffs in the Waiahulu region of the island of Kauaʻi, in an area previously unexplored due to its extreme terrain.

This discovery, published in the open-access journal PhytoKeys, was made possible through the National Tropical Botanical Garden's (NTBG) botanical drone program, which deploys unmanned aircraft to explore remote cliff environments.

In collaboration with Quebec-based Outreach Robotics, NTBG developed ‘the Mamba,’ a remote plant collection device specifically designed for vertical cliff work. This device was suspended from a drone and used to grab, cut, and collect the plant for study.

The new species belongs to a well-studied Hawaiian lineage in the carnation family. Its genus, Schiedea, consists of 36 species spread across the Hawaiian Islands, with 12 species found only on Kauaʻi.

Schiedea waiahuluensis is found only on the dry cliffs of Waiahulu, with an estimated population of around 345 individuals, primarily growing on bare rock surfaces in small pockets of soil. The fragile habitat is under threat from invasive plant species and feral goats, making conservation efforts crucial. Further surveys are planned to assess the full distribution and conservation needs of the species.

Authors Stephen Weller and Ann Sakai from the University of California, Irvine note, “S. waiahuluensis has a combination of traits that would have been very difficult to predict, and upended our notions about diversity in Schiedea, even after decades of research on this genus.”

Lead author Warren Wagner, a research botanist at the Smithsonian Institution, states,“the new development of the NTBG drone program provides a major new tool in biodiversity research that has allowed for better assessment of species distribution and status as shown by drone missions on the inaccessible cliffs of the major canyons on Kauaʻi.

It has revealed populations of species presumed extinct such as the recent rediscovery of Hibiscadelphus woodii, a relative of Hibiscus, mapped populations of Schiedea waiahuluensis, and collected seeds via drone for establishment of a conservation collection of this species.”

This discovery, following more than 40 years of research on Schiedea on Kauaʻi, demonstrates the vast potential for future discoveries of native plants across the Hawaiian Islands through drone technology, and highlights the burgeoning role of drones in advancing conservation efforts and preventing plant extinctions.

Original study:

Wagner WL, Weller SG, Sakai AK, Nyberg B, Wood KR (2024) Schiedea waiahuluensis (Caryophyllaceae), an enigmatic new species from Kaua'i, Hawaiian Islands and the first species discovered by a drone collection system. PhytoKeys 247: 111-121. https://doi.org/10.3897/phytokeys.247.130241

Flower of drone collected specimen.

Credit

KR Wood.

Schiedea waiahuluensis habitat. A) Waiahulu branch of Waimea Canyon, drone photo. B) non-collected individual, drone photo.

Collecting arm hanging from drone.

Credit

Ben Nyberg

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Journal

PhytoKeys

DOI

10.3897/phytokeys.247.130241 

Article Title

Schiedea waiahuluensis (Caryophyllaceae), an enigmatic new species from Kaua'i, Hawaiian Islands and the first species discovered by a drone collection system

Article Publication Date

9-Oct-2024

 

Plants save energy when absorbing potassium

University of Würzburg

 

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Plants have two separate potassium uptake systems, the transporter HAK5 and the channel AKT1. Depending on the potassium concentration in the soil, one or the other system is responsible for the uptake of potassium into the roots. This ensures a constant supply of potassium even when potassium availability varies.

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Credit: Tobias Maierhofer / University of Wuerzburg

Potassium is one of the nutrients that plants need in large quantities. However, the amount of potassium in the soil can vary greatly: potassium-poor soils can contain up to a thousand times less of this nutrient than potassium-rich soils. To be able to react flexibly to these differences, plants have developed mechanisms with which they adapt their potassium uptake to the respective soil condition.

Like the cells of the human body, plant cells also work with an operating potassium concentration of around 100 millimolar. If the roots find a potassium source with a significantly lower concentration or only traces of it, they can only absorb the potassium into their cells by expending energy. This is achieved by the interaction between the potassium ion channel AKT1 and the potassium transporter HAK5.

Research is Relevant for Plant Breeding

‘Although HAK5 has been known since the late 1990s, its transport mechanism has so far remained largely unknown,’ says Professor Rainer Hedrich from Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany. A team led by the Würzburg biophysicist now wanted to elucidate this mechanism: ‘Knowledge about this is important when it comes to breeding crops that also produce yields on non-fertilised or only lightly fertilised fields, i.e. that can manage with less fertiliser.’

In their experiments, the Würzburg research group led by first authors Tobias Maierhofer and Sönke Scherzer benefited from their extensive experience with the potassium channel AKT1. The group now describes their results in detail in the journal Nature Communications.

Establishing a pH Gradient Costs Energy

For the AKT1 channel to transport potassium into the cells, higher soil potassium concentrations are required. The normal electric field of the cell membrane is sufficient as an energy source. The HAK5 transporter, on the other hand, already works at low soil potassium levels. In addition to the electric field, it needs the energy of the pH gradient. The plant must build up this gradient across the cell membranes, and this costs energy.

Further experiments showed that the potassium transporter HAK5 and the potassium channel AKT1 co-operate in an energy-saving manner when the potassium concentration in the soil fluctuates.

Transporter Must Have a Potassium Sensor

At high concentrations, the energy-guzzling transporter HAK5 is switched off. This means that the transporter must have a potassium sensor. In their search for the sensor, the Frankfurt structural biologist Inga Hänelt and her Würzburg colleague Thomas Müller made progress: they found a mutant of the transporter in which the affinity for potassium is 100 times lower.

‘Now it is important to explore in more detail the molecular reactions that trigger the mutation,’ says Rainer Hedrich, describing the next research goals. He also wants to find out how potassium transport into the root cell is mechanically and energetically coupled to proton transport.

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Journal

Nature Communications

DOI

10.1038/s41467-024-52963-6 

Method of Research

Experimental study

Subject of Research

Cells

Article Title

Arabidopsis HAK5 under low K+ availability operates as PMF powered high-affinity K+ transporter