Archive for the ‘Host plant resistance’ Category


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September 19, 2016
John Innes Centre
Plants have specialized immune receptor proteins on the surface of their cells, which detect specific molecular patterns, or ligands, on harmful bacteria. New research now reveals that these immune receptors, along with the ligand that activates them, must be taken up inside the plant cell in order to mount a full immune response to bacterial infection.

Pseudomonas syringae at stomata opening. This is a confocal microscopy image of Arabidopsis leaf surface infected with Pseudomonas syringae pv tomato DC3000 bacteria. These bacteria, fluorescing green, are present at the stomatal pores in order to invade the leaf. The chloroplasts are highlighted in purple.
Credit: Michael Kopischke, The Sainsbury Laboratory

Plants have specialised immune receptor proteins on the surface of their cells, which detect specific molecular patterns, or ligands, on harmful bacteria. New research by scientists at The Sainsbury Laboratory in Norwich now reveals that these immune receptors, along with the ligand that activates them, must be taken up inside the plant cell in order to mount a full immune response to bacterial infection.

When plants are attacked by harmful organisms, running away clearly isn’t an option — but that doesn’t mean they are powerless. Plants have clever molecular mechanisms that help them to detect and resist pests and pathogens. Scientists at The Sainsbury Laboratory in Norwich are interested in understanding how these immune processes work because this may be useful in breeding disease-resistant crops — especially when climate change threatens to bring new pests and diseases our way.

Working with an international team of collaborators, a new study, led by The Sainsbury Laboratory’s Professor Silke Robatzek and published in the journal Proceedings of the National Academy of Science of the USA, reveals new details about plant-triggered immunity.

Professor Robatzek explained, “We already knew that special protein molecules called ‘pattern recognition receptors’, the immune receptors located on the surface of plant cell membranes, can recognise specific ‘microbe-associated molecular patterns’, or MAMPs, from harmful bacteria. An immune receptor called FLS2 is a well-studied example — this can detect flagellin, a protein found in the tube-like filaments emanating from some bacterial cells that allows them to move. Several other receptors and the associated MAMPs or danger signals that activate them have been discovered, so we know that plants can detect and resist many different types of bacteria, but we were interested in what happens next — when the receptor is activated, what does it do? Where does it go? And how, exactly, does this help the plant to defend itself?”

To answer these questions, the research team used a technique called live cell imaging in which receptor proteins of interest were tagged with a fluorescent marker so that their movements could be visualised using a special microscope.

From previous work, the scientists knew that when FLS2 is activated, it is ‘internalised’. This means that it is moved from the plant cell membrane to a membrane-bound ‘bubble’ inside the cell called an endosome.

Postdoctoral scientist and co-first author of the study Dr Gildas Bourdais, said, “We discovered that several other receptors follow the same pattern as FLS2 — they too are internalised into endosomes, and they require another protein called clathrin to do so. We now show this is a common process conserved among many different immune receptors, and even danger-sensing receptors. Furthermore, we think that the process of internalisation is key to recycling the receptors so that plants stay in ‘defence mode’ in the long run.”

Plants may not be able to run away, but they do have several chemical weapons at their disposal, and can also ‘batten down the hatches’ by closing their stomata — the leaf pores that usually open to allow gas exchange, but which can be infiltrated by harmful bacteria. The scientists observed that stomata closed only when the receptor internalisation mechanism was functional, strongly suggesting that it is key to providing a level of immunity even before bacteria enter the plant.

Dr Bourdais said, “Having lots of specialised immune receptors means that plants can sense many different MAMPs, either from the same bacterial pathogen or different ones — but what happens next — clathrin-mediated internalisation of activated receptors — is a critical step for the plant to fully deploy it’s immune responses to pathogen attack.”

Story Source:

The above post is reprinted from materials provided by John Innes Centre. Note: Content may be edited for style and length.

Journal Reference:

  1. Malick Mbengue, Gildas Bourdais, Fabio Gervasi, Martina Beck, Ji Zhou, Thomas Spallek, Sebastian Bartels, Thomas Boller, Takashi Ueda, Hannah Kuhn, and Silke Robatzek. Clathrin-dependent endocytosis is required for immunity mediated by pattern recognition receptor kinases. Proceedings of the National Academy of Sciences, September 2016 DOI: 10.1073/pnas.1606004113

Cite This Page:

John Innes Centre. “Plants take it all in to deal with bacteria.” ScienceDaily. ScienceDaily, 19 September 2016. <www.sciencedaily.com/releases/2016/09/160919151221.htm>.

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Sept. 1, 2016

Tomato blight

Gregory Martin/Provided
Bacterial speck disease creates unattractive black spots on a ripe tomato, making it unmarketable.

Researchers at the Cornell-affiliated Boyce Thompson Institute (BTI) and Virginia Tech have discovered a new weapon in the arms race between plants and pathogenic bacteria, which tomatoes use to detect the microbe that causes bacterial speck disease.

The team identified a new receptor in tomato plants, called FLAGELLIN-SENSING 3 (FLS3), which triggers defenses against a bacterial attack. FLS3 is present in a small number of plant species, including tomato, potato and pepper. The study appears in Nature Plants.

“This is an interesting example of a receptor that appears to have evolved fairly recently because it is only found in a small group of plants,” said first author Sarah Hind, a research associate in the lab of BTI professor Gregory Martin. “This discovery sets up the possibility of introducing FLS3 into other economically important crop plants, which might provide resistance to bacterial pathogens that is not naturally present in those plants.”

FLS3 detects a part of the flagellum, a tail-like appendage that helps bacteria swim through their environment and consists mostly of flagellin proteins. When bacteria invade the plant, the FLS3 receptor binds to a region of the flagellin protein called flgII-28 and triggers an immune response.

FLS3 is the second flagellin sensor discovered in tomatoes. The first, called FLS2, is found in most land plants and detects invading bacteria through recognition of a separate region of flagellin. Several bacterial species have acquired mutations that change the shape of their flagellin so that FLS2 can no longer recognize it. The acquisition of the FLS3 receptor may, therefore, serve as a countermeasure on behalf of the tomato to detect bacteria with altered flagellin.

Martin and his colleagues worked with postdoctoral researcher Christopher Clarke and professor Boris Vinatzer at Virginia Tech, who previously identified flgII-28 as a conserved segment of the flagellin protein that tomatoes can detect. Additionally, Martin and other colleagues had screened heirloom tomato varieties and found that some, including Yellow Pear, could not respond to flgII-28, suggesting that the tomato must be missing FLS3.

“Discovering that some heirloom tomatoes, such as Yellow Pear, did not respond to flgII-28 was key to using a genetics approach to identify FLS3,” said senior author Martin, the Boyce Schulze Downey Professor at BTI and a Cornell professor in the School of Integrative Plant Science.

In the current paper, Hind used Yellow Pear tomatoes together with a wild relative of tomato called Solanum pimpinellifolium to identify the FLS3 gene and show how it functions to reduce bacterial growth. But to confirm that FLS3 is the receptor for flgII-28, she needed to demonstrate the two molecules can physically interact. Researchers in the laboratories of Martin and Frank Schroeder, BTI associate professor, developed biochemistry techniques to identify a stable complex between FLS3 and flgII-28, thus validating FLS3 as the flgII-28 receptor.

“Proving direct interactions of biomolecules has remained a huge challenge, and our work will help in developing better approaches for exploring receptor-ligand interactions,” said co-author Schroeder, who is also a Cornell professor in chemistry and chemical biology.

The study demonstrates how versatile the plant immune system can be while fighting a constant battle against infectious bacteria. “Plants are always coming up with new ways to defeat pathogens,” said Hind. “We’re trying to understand how they do it and then use this knowledge to develop more disease-resistant plants.”

Additional BTI researchers on the project include research associate Susan Strickler and graduate students Joshua Baccile and Jason Hoki. Former BTI researchers include postdoctoral scientists Patrick Boyle and Zhilong Bao, research assistant Diane Dunham, graduate student Inish O’Doherty, and undergraduate intern Elise Viox.

Patricia Waldron is the staff science writer for the Boyce Thompson Institute.

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From PestNet

Researchers Create Plant that Grows Fast and Defends Itself from Insects

Section: News from Around the World

A team of researchers from Michigan State University (MSU) has developed a plant that can outgrow and outcompete its neighbors for light, and defend itself against insects and disease.

Led by Gregg Howe, MSU Foundation professor of biochemistry and molecular biology, the team modified an Arabidopsis plant by “knocking out” both a defense hormone repressor and a light receptor in the plant. This genetic alteration allowed the plant to grow faster and defend itself from insects at the same time.

In plants, more growth equals less defense, and more defense equals less growth, but Howe said that their “genetic trickery” can get a plant to do both. If the results of this breakthrough can be replicated in crop plants, the work could have direct benefits for farmers trying to feed a world population that is expected to reach nine billion by the year 2050.

For more details, read the news release at MSU Today.

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New York Times


Cherry tomatoes. Researchers found that domesticated tomatoes like these were less resistant to whiteflies than currant tomatoes, a wild species. Credit Dean Fosdick/Associated Press

Whiteflies are the scourge of many farms, damaging tomatoes, peppers, eggplants and other crops. Now, researchers in Britain report that a species of wild tomato is more resistant to the pest than its commercial counterparts.

The wild type, the currant tomato, is closely related to domestic varieties, “so we could crossbreed to introduce the resistance,” said Thomas McDaniel, a biologist and doctoral student at Newcastle University in England and a co-author of the study, published in the journal Agronomy for Sustainable Development. “Another method would be genetic engineering, if we identified the genes.”

The researchers studied Trialeurodes vaporariorum, a species of whitefly that often attacks tomatoes grown in greenhouses. Whiteflies damage tomato plants by extracting the plant’s sap, which contains vital nutrients; by leaving a sticky substance on the plant’s surface that attracts mold; and by transmitting viruses through their saliva.

But currant tomatoes have some sort of mechanism, yet to be understood, that repels whiteflies. “They seemed to move away every time they tried to sample the sap,” Mr. McDaniel said.

The wild plants also produce a chemical reaction that causes the plant sap to gum up the whitefly’s feeding tube.

Growers use a parasitic wasp to control whiteflies. The wasp lays its eggs on young whiteflies, which are eaten by hatching larvae. The treatment is expensive and laborious. As an alternative, farmers use chemical pesticides, but some have been linked to declines in bee populations.

“Genetic diversity is very, very low in domestic crops, so introducing these genes that we’ve lost along the way is probably quite important,” Mr. McDaniel said.

Continue reading the main story


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Chiapas, Mexico, July 25, 2016

Felix Corzo Jimenez , a farmer in Chiapas, Mexico, examines one of his maize plants infected with tar spot complex.
Felix Corzo Jimenez , a farmer in Chiapas, Mexico, examines one of his maize plants infected with tar spot complex. Photo: J. Johnson/CIMMYT.

In southern Mexico and Central America a fungal maize disease known as tar spot complex (TSC) is decimating yields, threatening local food security and livelihoods. In El Portillo, Chiapas, Mexico, local farmer Felix Corzo Jimenez sadly surveys his maize field.

“It’s been a terrible year. We’ll be lucky if we harvest even 50 percent of our usual yields,” he said, examining a dried up maize leaf covered in tiny black dots, and pulling the husk off of an ear to show the shriveled kernels, poorly filled-in. “Tar spot is ruining our crops.”

Named for the black spots that cover infected plants, TSC causes leaves to die prematurely, weakening the plant and preventing the ears from developing fully, cutting yields by up to 50 percent or more in extreme cases. Caused by a combination of three fungal infections, the disease occurs most often in cool and humid areas across southern Mexico, Central America and South America. The disease is beginning to spread – possibly due to climate change, evolving pathogens and susceptible maize varieties – and was reported in important maize producing regions of central Mexico and the northern United States for the first time last fall. To develop TSC resistant maize varieties that farmers need, the Seeds of Discovery (SeeD) initiative is working to “mine” the International Maize and Wheat Improvement Center’s (CIMMYT) genebank for native maize varieties that may hold genes for resistance against the disease.

The first stage of fungal maize disease TSC, with tiny, black “tar spots” covering the leaf. The spots will soon turn into lesions that kill the leaf, preventing photosynthesis from occurring.

The majority of maize varieties planted in Mexico today are susceptible to TSC, meaning that farmers would have to spray expensive fungicides several times each year to protect their crops against the disease, a huge financial burden that few can afford. Creating varieties with natural resistance to tar spot is an economical and environmentally friendly option that will protect the livelihoods of the region’s smallholder maize farmers.

“This project targets the many farmers in the region with limited resources, and the small local seed companies that sell to farmers at affordable prices,” says Terry Molnar, SeeD maize breeder.

The key to developing maize varieties with resistance to TSC lies in the genetic diversity of the crop. For thousands of years, farmers have planted local maize varieties known as landraces, or descendants from ancient maize varieties that have adapted to their environment. Over centuries of selection by farmers these landraces accumulated specific forms of genes, or alleles, which helped them to resist local stresses such as drought, heat, pests or disease.

These novel genetic traits found in landrace maize can help breeders develop improved maize varieties with resistance to devastating diseases such as TSC. However, it is quite challenging for breeders to incorporate “exotic” landrace materials into breeding programs, as despite their resistance to stresses found in their native environment, they often carry unfavorable alleles for other important traits.

A maize ear with shriveled kernels that are poorly filled, a major side effect of TSC that reduces farmer’s tields.

To help breeders incorporate this valuable genetic diversity into breeding programs, SeeD works to develop “bridging germplasm” maize varieties, which are created by transferring useful genetic variation from landraces held in the CIMMYT genebank into plant types or lines that breeders can readily use to develop the improved varieties farmers need. These varieties are created by crossing landrace materials with CIMMYT elite lines, and selecting the progeny with the genetic resistance found in a landrace without unfavorable traits breeders, farmers and consumers do not want.

“The CIMMYT maize genebank has over 28,000 maize samples from 88 countries, many of which are landraces that may have favorable alleles for disease resistance,” Molnar says. “We all know that there is good material in the bank, but it’s scarcely being used. We want to demonstrate that there are valuable alleles in the bank that can have great impact in farmers’ fields.”

A susceptible maize variety infected with TSC (left) compared to a healthy maize plant , a resistant variety immune to the disease (right).

SeeD scientists began by identifying landrace varieties with genetic resistance to TSC. Trials conducted in 2011, 2012 and 2014 evaluated a “core set” – a genetically diverse subset of the maize germplasm bank – in search of resistant varieties.  Of the 918 landrace varieties planted in 2011 and 2012, only two landraces—Oaxaca 280 and Guatemala 153—were outstanding for tolerance to the disease.  Genotypic data would later confirm the presence of unique resistant alleles not currently present in maize breeding programs that could be deployed into SeeD’s bridging germplasm. This bridging germplasm will be available to breeders for use in developing elite lines and varieties for farmers.

“As a breeder, I’m excited to work with SeeD’s bridging germplasm as soon as it is available,” said Felix San Vicente, CIMMYT maize breeder working with the CGIAR Research Program on Maize and the Sustainable Modernization of Traditional Agriculture (MasAgro) project.

Terry Molnar, maize breeder with SeeD, and Enrique Rodriguez, field research technician with SeeD, evaluate bridging germplasm for resistance to TSC.

Up to this point, most breeders have only used elite lines to develop hybrids, because landraces are extremely difficult to use. This practice, however, greatly limits the genetic diversity breeders employ. Using novel alleles from maize landraces allows breeders to develop improved hybrids while broadening the genetic variation of their elite germplasm. This novel genetic diversity is very important to protect crops from evolving pathogens, as it means the varieties will have several resistant alleles, including alleles that have never been used in commercial germplasm before.

“The more alleles the better,” said San Vicente, “as it protects the line longer. It provides a form of insurance to smallholder farmers as these varieties will have more genes for resistance, which reduces their risk of losing their crop.”

To ensure that farmers can access this improved seed, CIMMYT works with small local seed companies. “The price of seed will be very affordable,” according to San Vicente. “As CIMMYT is a non-profit, we provide our improved materials to seed companies at no cost.”

The TSC resistant bridging germplasm developed by SeeD has been tested in on-farm trials in TSC-prone sites in Chiapas and Guatemala, with promising results, and will be publicly available to breeders in 2017. In the meantime, local farmers look forward to seeing the results of this research in their own fields. “A variety with the disease resistance of a landrace and the yield and performance of a hybrid is exactly what we need,” says Corzo Jimenez.

Corzo Jimenez in his maize field infected with TSC. Varieties made from SeeD bridging germplasm would allow him to protect his crop without applying expensive fungicides.

Corzo Jimenez in his maize field infected with TSC. Varieties made from SeeD bridging germplasm would allow him to protect his crop without applying expensive fungicides. CIMMYT/Jennifer Johnson.

SeeD is a multi-project initiative comprising: MasAgro Biodiversidad, a joint initiative of CIMMYT and the Mexican Ministry of Agriculture (SAGARPA) through the MasAgro (Sustainable Modernization of Traditional Agriculture) project; the CGIAR Research Programs on Maize (MAIZE CRP) and Wheat (WHEAT CRP); and a computation infrastructure and data analysis project supported by the UK’s Biotechnology and Biological Sciences Research Council (BBSRC). To learn more about the Seeds of Discovery project, please go to http://seedsofdiscovery.org/.


More news from: CIMMYT (International Maize and Wheat Improvement Center)


Website: http://www.cimmyt.org

Published: July 26, 2016


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From the Ohio State University Vegetable Newsletter

Matt Kleinhenz, Department of Horticulture and Crop Science, The Ohio State University

Many articles, including one in the June 21 edition of VegNet, have stated that grafted fresh market tomato plants can out-yield ungrafted ones by up to 50% or more depending on the circumstances. Those circumstances appear to include abiotic and biotic stresses that also occur in processing tomato production in Ohio and elsewhere. In some tests, grafted fresh market tomato plants have also out-yielded ungrafted ones when lower rates of fertilizer were used.

So, at first glance, it seems obvious that grafted plants will also be useful in processing tomato production. However, that has not been proven. Clearly, more information is needed to understand the value of grafted plants in processing tomato production. Their value is increasing in fresh market production and their potential to enhance processing production is real. That said, differences between fresh market and processing tomato production, including their economics and varieties, requires the value of grafted plants in processing production to be validated separately. Grafting effects on processing tomato yield, quality, and profit potential must be tested thoroughly.

Growers, researchers, and others must do the testing. Teams in California and Ohio have started. Currently, as described in Figure 1, plots at the OARDC in Wooster, OH contain plants representing thirty rootstock-scion variety combinations and ungrafted plants of the fruiting (scion) varieties. We are tracking crop development and we will record fruit yield and quality, including color and soluble solids. Our work is supported by The Ohio Vegetable & Small Fruit Research & Development Program (OVSFRDP), the USDA-SCRI program, The OSU-OARDC, and the Department of Horticulture and Crop Science. We will be happy to assist growers with tests on their farms. Contact Matt Kleinhenz (ph. 330.263.3810; kleinhenz.1@osu.edu) for more information. Also, see resources at http://www.vegetablegrafting.org/ for additional information.



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