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

An unsustainable trade

Guest post by Isabella Whitworth (@Orchella49).

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Roccella gracilis on wool yarn that has been dyed with orchil made from Lasallia pustulata. Image credit: Isabella Whitworth .

Lichens are complex plant-like organisms made up of a fungus and an alga or cyanobacterium that live together in a mutually beneficial relationship (symbiosis). They are often found attached to rocks or trees and species can vary hugely in appearance, from flat, crusty forms to leaf-like growths. Certain species have been used as dyestuffs for millennia, although not all lichens produce dye.

My research into dye lichens was triggered by a chance mention of ‘an archive in the attic’ by local friends. Their forebears were dye manufacturers in nineteenth century Leeds in the UK and the company archive had been passed down three generations. The company’s initial fortunes came from the successful processing of orchil, a dye made from lichens. Continue reading

Sex change by fungus

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White campion infected with anther smut fungus. Image by Martin C. Fischer (CC BY 4.0)

Fungi reproduce by releasing spores that lie dormant in the environment until conditions are right for them to grow. The spores of fungi that infect plants are often released from fungal structures that develop on the surface of their hosts’ leaves or stems. However, the anther smut fungus (Micobrotryum lychnidis-dioicae) employs a more unusual strategy. Its spores are displayed on its host’s flowers so that they can be carried to other plants by insect pollinators.

Anther smut fungus can infect a small flowering plant called white campion (Silene latifolia). White campion is dioecious, meaning that each plant can only produce either male or female flowers. In the flowers of the male plants, pollen is produced by structures called stamens. When the fungus infects a male plant, it manipulates the plant so that the stamens no longer produce pollen and display fungal spores instead. Continue reading

The helpful onion

Field of onions in Ismaning, Germany. Image by Rainer Haessner (CC BY SA 3.0 via Wikimedia Commons)

Field of onions in Ismaning, Germany. Image by Rainer Haessner (CC BY SA 3.0 via Wikimedia Commons)

This month it was all change in my vegetable patch as I harvested the last of the crops I planted in the spring and planted new things to grow over the winter. On a bit of whim I decided to plant some onion sets (mini bulbs) at one end of the patch, which should be ready to eat in early summer next year.

Onion is one of the oldest known cultivated plants and the earliest archaeological evidence of onions in human settlements dates back to around 5000 BC (Bronze age). It is grown all over the world where it features as a staple vegetable in a variety of dishes. It is not clear where they originated from, but there is some evidence that they may have come from southwestern Asia. Most cultivated onions are varieties of the common onion (Allium cepa L.) but some other onion species are cultivated too. Continue reading

Mind the GAP: understanding how rice plants defend against disease

Image by Mathieu Schoutteten via Flickr (CC BY-NC-ND 2.0)

Image by Mathieu Schoutteten via Flickr (CC BY-NC-ND 2.0)

Rice is the staple food for over 50% of the world’s population, but yields are threatened by rice blast, blight and other diseases caused by microbes. To protect our rice crops against these diseases, it is important that we understand how they can defend themselves against infection.

Plants have two defence systems that to allow them to identify and defend against microbes. The first system is a general response to the detection of molecules that are produced by many different microbes. For example, plants can detect chitin, which is the major component of the cell walls of fungi. So if a plant detects chitin it knows that there is a fungus lurking around and it can activate general defences. Continue reading

The potential of fungi to control invasive plants

By Aimee Fowkes (@AimeeFowkes)

A plant species is considered to be “invasive” in an area if it is not native and has a tendency to spread. Invasive plants can have a damaging effect on the new environment they find themselves in because they can outcompete the native flora and so interfere with the food web. Also, they may not have any natural enemies in their new location so they often show improved fitness and can grow uncontrollably.

I. glandulifera is also known as Himalayan balsam, Indian balsa and policeman’s helmet (owing to the shape of its flowers).  Image by ArtMechanic via Wikimedia Commons (CC BY-SA 3.0).

I. glandulifera is also known as Himalayan balsam, Indian balsa and policeman’s helmet (owing to the shape of its flowers). Image by ArtMechanic via Wikimedia Commons (CC BY-SA 3.0).

Impatiens glandulifera is a large flowering plant that originates from the western foothills of the Himalayas. It was introduced into Europe in the early nineteenth century as an ornamental plant, and it has since spread across Europe and North America. It grows on riverbanks, waste grounds and in woodlands.

Conventional control of I. glandulifera using chemicals has so far failed because it tends to grow in places that are inaccessible, or where use of herbicides is prohibited. This has led to investigations into an alternative solution, biological control.

Biological control is the use of one organism to reduce the population of another pest species, for example, by importing a natural enemy of the pest species into the new environment. Insects have been used in biological control since the nineteenth century, but it is only recently that people have started looking into using fungi to control weeds and invasive plants. There are several cases of fungi being used as biological control agents and their narrow host ranges reduce the risk that they will have an impact non-target species. Continue reading

The promise of drought-tolerant and disease-resistant barley

Image by Gerste Ähren (CC BY-SA 3.0)

Image by Gerste Ähren (CC BY-SA 3.0)

Barley is the fourth most important cereal crop in the world (behind rice, maize and wheat) and is grown in both temperate and tropical climates. It was one of the first grains to be domesticated and has a variety of uses including in the alcoholic drinks beer and whisky, as a foodstuff (especially in the Middle East) and for animal feed. Like other crops, the barley yields can be affected by many different pests and diseases, but also by adverse environmental conditions such as drought or low soil nutrients.

In July last year, I wrote about how a variety of barley called Golden Promise was genetically-modified to be more drought-tolerant (see previous post). This variety carries an extra copy of an existing barley gene—called HvSNAC1—that promotes the closure of pores (stomata) on the surface of barley leaves to reduce water loss when water is scarce (1). However, it was not known if making the plants more drought tolerant in this way could alter the ability of the plants to resist diseases caused by invading microbes.

Researchers at the John Innes Centre and SRUC studied that the ability of this variety to resist infection by several fungi that can cause diseases in barley (2). McGrann et al. found that the plants are more resistant to infection by a fungus called Ramularia collo-cygni. This fungus causes a disease called Ramularia leaf spot, a newly emerging disease that is currently affecting barley crops in Europe. Continue reading