Featured Research

from universities, journals, and other organizations

Plants Have A Double Line Of Defence

Date:
November 19, 2005
Source:
Max Planck Society
Summary:
Max Planck researchers in Cologne, Germany demonstrate that a multi-step defence system underlies the durable resistance of plants to fungal parasites. This research could be central to the development of new "green" fungicides.

The model plant Arabidopsis thaliana defends itself against an invading parasite. In one mutation of Arabidopsis, in which the PEN2-protein gene is switched off (right: plant, left: compared to wild type), the grass powdery mildew tries to penetrate the epidermis cells with a significantly higher frequency than in the wild type. The cells under attack eventually die from the invasion. The resulting white fluorescence can be seen with a UV-light. The red background colouring of the leaves is due to the fluorescence of the chlorophyll.
Credit: Image : Max Planck Institute for Plant Breeding Research/Volker Lipka

Plants are exposed to many different pathogens in the environment. Only a few of these pathogens, however, are able to attack a species of plant and "make it sick". If a particular pathogen is unable to attack a plant, that means that the plant is resistant to it -- in other words, it cannot host the pathogen.

This durable type of immunity of a plant to parasites is called nonhost resistance. Although, in nature, nonhost resistance stops almost all parasite attacks, it has been the subject of little research. Scientists from the Max Planck Institute for Plant Breeding Research in Cologne, working with Volker Lipka, Jan Dittgen, and Paul Schulze-Lefert, and in co-operation with colleagues from the Carnegie Institution in the US, have uncovered the molecular components of nonhost resistance and described this system of defence in the current edition of the journal Science (November 18, 2005). In their findings, they draw parallels between the immune systems of plants and animals. This research could be central to the development of new "green" fungicides.

The Max Planck researchers were able to identify the gene known as PEN (penetration) as an important component of nonhost resistance. They isolated arabidopsis mutations, which are partially susceptible to powdery mildews. If these genes are defective, or if the protein they code is missing in the plant cells, the fungus can invade the leaf epidermis cells more frequently. For that reason the scientists looked particularly at the question of exactly which function the PEN2 protein has in the defence against pathogens.

PEN2 is an enzyme located in the membrane of what are called peroxisomes. These are spatially separated cell compartments, in which metabolic reactions often take place that would be dangerous for the organism at any place other than inside the compartments. If a fungus tries to invade a plant cell, the peroxisomes are led over to the entry site by the attached PEN2 protein. One or more sugar molecules can be separated from another cell component through the enzyme activities of the PEN2 enzyme, a glycosyl hydrolase. The substance released by it appears to have a fungicidal effect, which kills the pathogen.

The researchers, on the other hand, observed that when PEN2 is missing, the plants become more susceptible not only to grass powdery mildew fungi but also other pests -- for example, the pathogens causing late potato blight. PEN2 is therefore a basic component of the plant's immune system with a broad range of effects.

However if PEN2 is missing, the plant is not completely helpless against fungal diseases. There is still another line of defence which they have to get through. If PEN2 is missing, the plant takes a drastic step: the cell dies together with its attacker, which protects the neighbouring plant tissue from infection.

In this deadly line of defence, very different proteins play a key role -- particularly EDS1, PAD4 and SAG101. They were already known to researchers in other species of plants, which identify molecular traits only present in parasites by using immune receptors both on the cell surface and inside the cell. Only if this second mechanism also fails can the originally non-virulent grass powdery mildew fungus colonise the plant.

The Max Planck research has now demonstrated that the nonhost resistance of plants develops out of a defence system with at least two steps. These steps determine whether a plant is susceptible to a disease or not. The redundancy of the defence layers and the wide-ranging effects of PEN2 explain why, in nature, nonhost resistance is a durable and broadly effective defence mechanism. If a building block is missing from one defence layer, its function will be taken over by components of the next layer.

Until now, scientists had assumed that nonhost resistance is based more on "passive" mechanisms: for example, the structure of the cell wall, poisonous substances on the surface of the plant, or a lack of molecular entry sites for pathogens. But the researchers in Cologne have now shown that active immune responses make a key contribution to nonhost resistance -- for example, the transport of PEN2 to the place of infection.

In further studies, the researchers hope to try to identify materials that are built up via PEN2 at the place of infection. They surmise that these materials could lead to the development of new kinds of "green fungicide" with a broad range of effects in the fight against plant diseases.


Story Source:

The above story is based on materials provided by Max Planck Society. Note: Materials may be edited for content and length.


Cite This Page:

Max Planck Society. "Plants Have A Double Line Of Defence." ScienceDaily. ScienceDaily, 19 November 2005. <www.sciencedaily.com/releases/2005/11/051119103606.htm>.
Max Planck Society. (2005, November 19). Plants Have A Double Line Of Defence. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2005/11/051119103606.htm
Max Planck Society. "Plants Have A Double Line Of Defence." ScienceDaily. www.sciencedaily.com/releases/2005/11/051119103606.htm (accessed July 31, 2014).

Share This




More Plants & Animals News

Thursday, July 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Visitors Feel Part of the Pack at Wolf Preserve

Visitors Feel Part of the Pack at Wolf Preserve

AP (July 31, 2014) Seacrest Wolf Preserve on the northern Florida panhandle allows more than 10,000 visitors each year to get up close and personal with Arctic and British Columbian Wolves. (July 31) Video provided by AP
Powered by NewsLook.com
Raw: Thousands Flocking to German Crop Circle

Raw: Thousands Flocking to German Crop Circle

AP (July 30, 2014) Thousands of people are trekking to a Bavarian farmer's field to check out a mysterious set of crop circles. (July 30) Video provided by AP
Powered by NewsLook.com
Peace Corps Pulls Workers From W. Africa Over Ebola Fears

Peace Corps Pulls Workers From W. Africa Over Ebola Fears

Newsy (July 30, 2014) The Peace Corps is one of several U.S.-based organizations to pull workers out of West Africa because of the Ebola outbreak. Video provided by Newsy
Powered by NewsLook.com
Concern Grows Over Worsening Ebola Crisis

Concern Grows Over Worsening Ebola Crisis

AFP (July 30, 2014) Pan-African airline ASKY has suspended all flights to and from the capitals of Liberia and Sierra Leone amid the worsening Ebola health crisis, which has so far caused 672 deaths in Guinea, Liberia and Sierra Leone. Duration: 00:43 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

    Environment News

    Technology News



    Save/Print:
    Share:

    Free Subscriptions


    Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

    Get Social & Mobile


    Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

    Have Feedback?


    Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
    Mobile: iPhone Android Web
    Follow: Facebook Twitter Google+
    Subscribe: RSS Feeds Email Newsletters
    Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins