Guest post: Garlic mustard across the pond

 

By Mercedes Harris

Spring has finally sprung, and forests are coming to life again. Green leaves are starting to emerge along with the first colorful flowers of the season. But not all green is good. Odds are that much of the green you’re seeing this spring comes from non-native plants, especially in residential communities. At first glance, these “pretty” invaders may not appear destructive, but take a closer look and a different picture emerges.

Invasive species are non-native organisms whose introduction causes environmental or economic harm. An invasive herbaceous plant native to Europe and Asia called garlic mustard (Alliaria petiolata) spreads across North American forests causing multiple problems. Its presence inhibits the survival of butterflies, stops the growth of tree seedlings, and minimizes food sources for mammals. How does a 100 cm plant cause so much havoc?

Eddmaps

Figure 1: Garlic mustard sightings in the United States reported to Early Detection and Distribution Mapping System (EDDMapS) 

Garlic mustard uses a variety of techniques to persist for years once introduced into new areas. Fast growth, chemical compounds that make it bitter tasting to herbivores, a cryptic rosette plant form, and hefty seed production all give garlic mustard an advantage over native wildflowers, shrubs, and tree seedlings. Garlic mustard grows quicker and taller than native plants crowding the space on the forest floor. Its chemical compounds are toxic to native butterflies and cut off the supportive fungi networks necessary for native tree seedling growth. It has a two-year growing season consisting of a basal rosette during the first year’s growth, which can go unnoticed in this form, but over-winters and bears flashy flowers in the early spring of the second growth year.

It produces high volumes of seeds to spread across landscapes; from roadsides to backyards, pastures to wetlands, hillsides, and prairies. Left unchecked, this plant forms dense populations wherever it goes. One single plant can produce anywhere from 350-7,900 seeds!

So, what can we do about this rapidly spreading herbaceous threat? Land managers commonly use two options, and neither is perfect. First, they can apply herbicide routinely. But this comes with the risk of applying herbicide onto surrounding native plants too. Second, managers can put hours and hours of manual labor into removing existing plants by hand, but garlic mustard has a large root that, if left behind, will regenerate next year.

Alliaria_petiolataseeds

Paul Henjum (public domain)

While land managers are still adjusting methods of garlic mustard removal and eradication, there are some things that everyone can do to limit the spread of garlic mustard and other invasive species. 1) When hiking, remain on marked trail ways to avoid spreading plant seeds. 2) In invaded areas, check shoes and clothing for seeds and remove them before leaving parks and trails. 3) Do not pick the flowers or open the seed pods as this will increase the seed dispersal range. 4) If spotted, report sightings of populations to land owners, or online invasive species detection databases such as EDDMapS.org.

About the author: Mercedes Harris is a recent graduate from the University of Massachusetts Amherst where she received a master’s degree in environmental conservation. She’s a biologist turned plant ecologist because the zoology courses always filled up too quickly during enrollment but the plant courses turned out to be great.

References:

EDDMapS. 2018. Early Detection & Distribution Mapping System. The University of Georgia – Center for Invasive Species and Ecosystem Health. Available online at http://www.eddmaps.org/; last accessed May 31, 2018.

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How a virus gives back to its host

 

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Image by F_A (CC BY 2.0)

A study by UK scientists has shown that tomato plants infected with a virus are more attractive to bumblebees than healthy plants. Why would a plant virus want to change the behaviour of bumblebees?

The virus in question – cucumber mosaic virus (CMV) – can infect many different species of plant including tomatoes and a model plant called Arabidopsis thaliana. In tomatoes it causes many symptoms including yellowing, mottling, leaf distortion and can reduce the yield of seeds. As a result there is pressure for populations of plants to evolve better defences against the virus. Since CMV can only multiply within plant cells you might expect that, over time, CMV might become less common, but this doesn’t appear to be the case. One way the virus might be able to combat this problem is to compensate for the decrease in seed production in infected plants by encouraging pollinators, such as bumblebees, to visit the flowers.

Bumblebees fertilise tomato flowers by a process called buzz pollination, in which sounds produced by the bees shake the flowers to release pollen. Although tomato flowers can fertilise themselves without help from the bumblebees, buzz pollination makes the process more efficient and also leads to the transfer of pollen between flowers. Volatile compounds (molecules that easily become gases) released from the plants may help to guide the bees to the flowers. CMV infection can change the mix of volatile compounds that plants produce, but it was not clear whether this changes the behaviour of the bees.

Simon Groen, Sanjie Jiang, Alex Murphy, Nik Cunniffe et al. found that the bees are more attracted to the volatiles produced by CMV-infected tomato plants than those produced by healthy, uninfected plants. In the absence of buzz pollination, CMV-infected plants produce fewer seeds than healthy plants. However, mathematical modeling indicates that, in the “wild”, the bee’s preference for virus-infected flowers may help to compensate for this so that CMV-infected plants may produce more seeds than uninfected plants. Further experiments in A. thaliana suggest that molecules of micro ribonucleic acid (or miRNA for short) produced by the plants might regulate the mix of volatiles that plants produce.

These findings suggest that in some environments it may be in a virus’ interest to help its host plant by making the plant more attractive to bumblebees or other pollinators. Bumblebees are important pollinators for many crop plants so these findings may help us to develop new ways to increase crop yields in the future.

Reference: Groen SC, Jiang S, M, Murphy AM, Cunniffe N, Westwood JH, Davey MP, Bruce TJA,  Caulfield JA, Furzer O, Reed A, Robinson SI, Miller E, Davis CN, Pickett JA, Whitney HM,  Glover BJ, Carr JP. 2016. Virus Infection of Plants Alters Pollinator Preference: A Payback for Susceptible Hosts? PLOS Pathogens http://dx.doi.org/10.1371/journal.ppat.1005790

Tracing the roots of an ancient friendship

 

Figure 1

An AM fungus (yellow) contacts the surface of a plant root. The nuclei of the plant cells are visible as blue spots. Image adapted from ref 3. Credit: Andrea Genre and Mara Novero (CC BY 3.0).

Plants need nutrients to be able to grow. Unfortunately, many of these nutrients can be scarce in the soil and therefore hard to get hold of. To get around this problem, most plants are able to form friendly relationships – known as symbioses – with soil microbes that can provide them with certain nutrients in exchange for sugars.

Today, around 80% of land plants form symbioses with a group of fungi known as arbuscular mycorrhizal (AM) fungi (1). Fossil evidence suggests that this symbiosis first emerged around 450 million years ago. This is around the same time that plants first started to colonise land. The transition from water to the dry and harsh environments on land would have presented many challenges to the early land plants, for example, how to avoid losing too much water. Another challenge would have been how to access essential nutrients that their ancestor (a type of green algae) would have gained directly from the water.

The liverworts, hornworts and mosses are thought to be the earliest groups of land plants (2). Since the AM symbiosis is widespread in these groups, it has been suggested that this symbiosis is one of the innovations that helped these primitive plants to survive on land.

Previous studies have identified many plant genes that are needed for AM symbiosis in legumes and other land plants. These genes can be split into two main groups: some are in a signalling pathway needed for the plant and fungus to communicate with each other, and others are activated later to allow the fungus to infect into the roots of the plant. Recently, Pierre-Marc Delaux and colleagues used a technique called phylogenetics to analyse genetic material from many different algae, liverworts, hornworts and mosses with the aim of finding out when the AM symbiosis genes first appeared (2).

Delaux et al. show that these plant genes emerged in stages, starting from before earliest plants colonised land. The signalling pathway genes appeared first, and are present in the algae that are thought to be the closest relatives of land plants, the Charophytes (2). On the other hand, the infection genes appear to be missing from the algae, but are present in the liverworts, hornworts and mosses.

These findings suggest that the algal ancestors of land plants were pre-adapted to interact with fungi. Currently, there is no evidence to suggest that the Charophytes are able to form AM symbioses themselves. Therefore, it is possible the signalling pathway evolved to allow algae to interact with other microbes and was later altered to allow the early land plants to interact with AM fungi.

Reference:

  1. Parniske, M. (2008). Arbuscular mycorrhiza: the mother of plant root endosymbioses. Nat Rev Microbiol, 6, 763-75.
(Good review of AM symbiosis, but unfortunately this article is hidden behind a paywall…)
  2. Delaux P, Radhakrishnan GV, Jayaraman D, Cheema J, Malbreil M, Volkening JD, Sekimoto H, Nishiyama T, Melkonian M, Pokorny L, Rothfels CJ, Sederoff HW, Stevenson DW, Surek B, Zhang Y, Sussman MR, Dunand C, Morris RJ, Roux C, Wong GK-S, Oldroyd GED, Ané JM. 2015. Algal ancestor of land plants was preadapted for symbiosis. Proceedings of the National Academy of Sciences of the United States of America. 2015, DOI: 10.1073/pnas.1515426112, PMID: 26438870
  3. Corradi N, Bonfante P. 2012. The Arbuscular Mycorrhizal Symbiosis: Origin and Evolution of a Beneficial Plant Infection. PLoS Pathog 8(4): e1002600. doi:10.1371/journal.ppat.1002600

Peer mentoring & why you should, too

Guest post by Liz Haswell (@ehaswell)

mentoring

Image licensed under CC BY-SA 3.0 NY via Google (author not known).

Mentoring programs are believed to be essential to a successful career in science and are considered a critical step in improving the retention of women and under-represented minorities in science, engineering and technology fields*. Traditional mentoring matches a junior or inexperienced person—the mentee—with someone senior or more experienced—the mentor. The topic of today’s post is a different kind of mentoring, which I am calling “peer mentoring**”. In this case, each participant is both a mentor and a mentee. Over the last 15 years, I have been involved in several different peer-mentoring groups, and in every case they have been a powerful source of personal and professional growth. Here, I explain what I mean by peer mentoring, describe my own experiences, and list some suggestions for starting your own group.

One possible format for a peer-mentoring group is laid out in the book Every Other Thursday: Stories and Strategies from Successful Women Scientists. Ellen Daniell describes her experience as part of a group of women faculty—including beloved University of California, San Francisco (UCSF) professors Carol Gross and Christine Guthrie—as they meet every two weeks to set goals and troubleshoot challenges. Though this book is more memoir than instruction manual, it explains in detail how the group members established a rigorous yet supportive framework that helped them to be as productive as possible during their meetings, and how the work they did in “group” improved their personal and professional lives.  Continue reading