- Author: Kathy Keatley Garvey
The research, “Root-Knot Nematodes Produce Functional Mimics of Tyrosine-Sulfated Plant Peptides,” is published in the current edition of the Proceedings of the National Academy of Sciences (PNAS).
It's like hijacking plant development to facilitate parasitism, according to nematologist Shahid Siddique, an associate professor in the Davis Department of Entomology and Nematology and one of the corresponding authors of this study. “This finding showcases an amazing case of convergent evolution across three different types of organisms, revealing how diverse life forms can develop similar strategies for survival.”
The root-knot nematode, which threatens global food security, is a small worm-like organism that is a highly evolved obligate parasite, or an organism that cannot survive without its host. It is known to infest some 2000 crops worldwide. “These parasites have a remarkable ability to establish elaborate feeding sites in roots, which are their only source of nutrients throughout their life cycle,” the authors wrote.
“Root-knot nematodes are a major threat to various crops, including fruit trees and vegetables,” Siddique said. “In California, tomatoes, almonds, and walnuts are among the major hosts susceptible to root-knot nematode infection.”
Siddique and UC Davis distinguished professor Pamela Ronald, a plant pathologist and geneticist in the Department of Plant Pathology and the Genome Center, are the joint corresponding authors. Joint first-authors are Henok Zemene Yemer, formerly of the Siddique lab and now with Gingko Bioworks, Emeryville, and Dee Dee Lu of the Ronald lab.
The team also included emerita professor Valerie Williamson of the former Department of Nematology; Maria Florencia Ercoli, postdoctoral fellow in the Ronald lab; Alison Coomer Blundell, a doctoral candidate in the Siddique lab; and Paulo Vieira of the USDA's Mycology and Nematology Genetic Diversity and Biology Laboratory, Beltsville, Md.
“Plant peptides containing sulfated tyrosine (PSY)-family peptides are peptide hormones that promote root growth via cell expansion and proliferation,” the authors explained. “A PSY-like peptide produced by a bacterial pathogen has been shown to contribute to bacterial virulence. Here, we discovered that PSY-like peptides are encoded by a group of plant-parasitic nematodes known as root-knot nematodes. These nematode-encoded PSY mimics facilitate the establishment of parasitism in the host plant. Our findings are an example of a functional plant peptide mimic encoded by a phytopathogenic bacterium (prokaryote) and a plant-parasitic nematode (an animal).”
The research involved gene expression analysis and parasitism of tomato and rice plants.
The project drew financial support from a collaborative grant awarded to Siddique and Ronald from the National Science Foundation's Division of Integrative Organismal Systems.
Siddique, a member of the UC Davis faculty since 2019, focuses his research on basic as well as applied aspects of interaction between parasitic nematodes and their host plants. “The long-term object of our research is not only to enhance our understanding of molecular aspects of plant–nematode interaction but also to use this knowledge to provide new resources for reducing the impact of nematodes on crop plants in California.”
Ronald, noted for her innovative work in crop genetics, especially rice, is recognized for her research in infectious disease biology and environmental stress tolerance. Thomson Reuters named her one of the world's most influential scientific minds and Scientfic American recognized her as among the world's 100 most influential people in biotechnology. In 2022 Ronald received the Wolf Prize in Agriculture.
The next steps? “Currently, we are working to understand the mechanism by which these peptides contribute to the nematode infection,” Siddique said. “This entails the characterization of receptors involved and gaining insights into transcriptional changes.”
- Author: Kathy Keatley Garvey
Kaloshian will speak on "Root-Knot Nematode Perception and Immune Signaling in Arabidopsis" at a hybrid seminar, both in-person and virtual, at 4:10 p.m., Wednesday, June 1 in 122 Briggs Hall. The Zoom link is https://ucdavis.zoom.us/j/99515291076.
Kaloshian will discuss her recent research, "A G-lectin Receptor Kinase is a Negative Regulator of Arabidopsis Immunity Against Root-Knot Nematode Meloidogyne incognita," published in bioRxiv in October 2021. She and her colleagues found that "A plasma membrane localized G-lectin receptor kinase acts as a negative immune regulator by interfering with defense responses activated by nematode and microbial elicitors."
"Root-knot nematodes (Meloidogyne spp., RKN) are responsible for extensive crop losses worldwide," she and her colleagues wrote in their abstract. "For infection, they penetrate plant roots, migrate between plant cells, and establish feeding sites, known as giant cells, in the root pericycle. Previously, we found that nematode perception and early plant responses were similar to those for microbial pathogens and require the BAK1 co-receptor in Arabidopsis thaliana and tomato. To identify additional receptors involved in this process, we implemented a reverse genetic screen for resistance or sensitivity to RKN using Arabidopsis T-DNA alleles of genes encoding transmembrane receptor-like kinases. This screen identified a pair of allelic mutations with enhanced resistance to RKN in a gene we named ENHANCED RESISTANCE TO NEMATODES 1 (ERN1). ERN1 encodes a G-type lectin receptor kinase (G-LecRK) with a single pass transmembrane domain. Further characterization showed that ern1 mutants displayed stronger activation of MAP kinases, elevated levels of the defense marker MYB51, and enhanced H202 accumulation in roots upon RKN elicitor treatments. Elevated MYB51expression and ROS burst were also observed in leaves of ern1 mutants upon flg22 treatment. Complementation of ern1.1 with 35S- or native promotor-driven ERN1 rescued the RKN infection and enhanced defense phenotypes. Taken together, our results indicate that ERN1 is an important negative regulator of immunity."
Kaloshian, who joined the UC Riverside faculty in 1997 and chaired the Department of Nematology from 2017-2021, was named divisional dean on July 1, 2021. During her three-year term, she is overseeing four departments: Botany and Plant Sciences, Entomology, Environmental Sciences, and Nematology.
As a molecular geneticist, Kaloshian studies the interactions between plants and nematodes, and insect pests. Her grants have been funded by the National Institute of Food and Agriculture and the National Science Foundation. She has served as a senior editor of journals in her field of research. (See UC Riverside news story)
Kaloshian is a fellow of the American Association for the Advancement of Science and a recipient of the Syngenta Award for Excellence in Research from the Society of Nematologists. Her other honors include the Chancellor's Award for Excellence in Undergraduate Research and Creative Achievement, and the UC Riverside Distinguished Service Award for her development of the COVID-19 campus testing lab.
Kaloshian holds a bachelor of science degree in agricultural engineering and master's degree in plant protection from American University of Beirut. She obtained her doctorate in plant pathology from UC Riverside and completed her postdoctoral training at UC Davis.
Hosting the seminar is coordinator Shahid Siddique, assistant professor, UC Davis Department of Entomology and Nematology. For any technical issues, contact him at ssiddique@
- Author: Kathy Keatley Garvey
The display will include:
- What's in the jar?
- Celery infected with root-knot nematodes
- Tree swallow infected with Diplotriaena
- White-tailed deer eye infected with a Thelazia species
- Peach root infected with root-knot nematodes
- Mormon crickets infected with Gordius robustus
- Lettuce infected with root-knot nematodes
- Garlic damaged by Ditylenchus dipsaci
- Horse stomach infected with three parasites: Parascaris (roundworms), tapeworms, and botfly larvae.
- Grape roots infected with root-knot nematodes
- Sweet potato infected with root-knot nematodes
- Sugar beet infected with cyst nematodes
- Peach root infected with cyst nematodes
- Sugar beet infected with root-knot nematodes
- Ascaris lumbricoides (roundworm)
- Minke whale infected infected with ascaridoid nematodes
- Heartworm of dog
The event is set for 11 a.m. to 3 p.m. in the UC Davis Conference Center, 555 Alumni Lane. Admission and parking are free, but visitors must adhere to the COVID-19 Campus Ready guidelines. Masks will be required in accordance with campus policies, organizers said. Visitors can also sign up at the Conference Center for limited tours. Several museums or collections will be offering tours. (See news story)
"Plant-parasitic nematodes are destructive pests causing losses of billions of dollars annually," Siddique says on his website. "Economic, health, and environmental considerations make natural host plant resistance a preferred strategy for nematode control, but there are limitations to this approach. In many cases, the resistance conferred by resistance genes is partial, and some of the nematodes are able to survive. Similarly, nematode resistance genes are often effective against only one or a few species, whereas plants are exposed to several pathogens in the field. Another concern is the emergence of pathotypes that can overcome resistance. In view of all these limitations, it is important to identify additional mechanisms and tools that can be used to develop novel and sustainable approaches to the management of nematodes."
"Research in the Siddique lab focuses on basic as well as applied aspects of interaction between parasitic nematodes and their host plants," Siddique points out on his website. "The long-term object of our research is not only to enhance our understanding of molecular aspects of plant–nematode interaction but also to use this knowledge to provide new resources for reducing the impact of nematodes on crop plants in California."
Coomer, a second-year doctorate student, recently won a worldwide competition competition sponsored by the International Federation of Nematology Societies (IFNS) for her three-minute thesis on root-knot nematodes. She delivered her video presentation virtually on “Trade-Offs Between Virulence and Breaking Resistance in Root-Knot Nematodes.” She will be awarded a busary and plaque at the 7th International Congress of Nematology (ICN), set May 1-6 in Antibes, France.
Coomer earlier was selected one of the nine finalists in the 22-participant competition, vying against eight other graduate students from the University of Idaho, Moscow; and universities in England, Australia, Brazil, Ireland, Kenya, Belgium and South Africa.
The UC Davis Biodiversity Museum Day is traditionally held on the Saturday of Presidents' Day weekend. However, last year's event was virtual, and this year's event is centrally located in an exposition. For more information, access the UC Davis Biodiversity Museum Day website and/or connect with Instagram,Twitter, and Facebook.
- Author: Kathy Keatley Garvey
Coomer, a member of the laboratory of nematologist Shahid Siddique of the UC Davis Department of Entomology and Nematology, just won a world-wide competition sponsored by the International Federation of Nematology Societies (IFNS) for her three-minute thesis on root-knot nematodes.
She delivered her video presentation virtually on “Trade-Offs Between Virulence and Breaking Resistance in Root-Knot Nematodes.” She will be awarded a busary and plaque at the 7th International Congress of Nematology (ICN), set May 1-6 in Antibes, France.
Coomer earlier was selected one of the nine finalists in the 22-participant competition, vying against eight other graduate students from the University of Idaho, Moscow; and universities in England, Australia, Brazil, Ireland, Kenya, Belgium and South Africa.
"Our entire lab is glad for Alison winning this award," said Siddique. "This is an outstanding performance and Alison has really been working hard for that. I feel proud about it. I am also looking forward to Alison's presentation at ICN."
Copeland discussed "Determining the Spatial Distribution of Pratylenchus quasitereoides/Pratylenchus curvicauda in the WA Wheatbelt, and Understanding How They Find Host Roots."
Sheehy's topic: Improving the Biological Control of Slugs: Understanding the Genome of Parasitic Nematode Phasmarhabditis hermaphrodita."
IFNS hosts the competition, IFNS 3-Minute Thesis, "to cultivate student academic and research communication skills, and to enhance overall awareness of nematodes and the science of nematology."
In her presentation, Coomer began with: “Root-knot nematodes, specifically the MIG-group, consisting of Meloidogyne incognita, javanica, and arenaria, are the most damaging of the plant parasitic nematodes causing severe yield loss in over 2,000 different plant species including tomatoes. The Mi-gene, which is a resistance gene in tomato, has been used in commercial farming and has been praised for its effectiveness towards the MIG group. This gene has been cloned but the mechanisms of how it's resistance works is still unknown.”
“We do know that with the presence of the MI gene, plants are more durable and will restrict infection and reproduction, by inducing an immune response within the plant,” Coomer pointed. “Although this resistance gene has been reliable for many decades, resistance breaking strains of root-knot nematodes have emerged threatening the tomato industry.”
Coomer related that her research “compares two strains of the root-knot nematode M. javanica. One strain is the wildtype, which has been isolated from fields, we will refer to it as VW4. This nematode can infect tomato plants, but when the MI gene is present, the nematode is blocked from successfully infecting. The other strain is a naturally mutated version of VW4. This strain breaks the resistance provided by the MI gene and therefore infects plants that contain the MI gene. I have labeled this strain as VW5. With the help of research like mine we can stay ahead of the resistance breaking strains and prevent major crop loss in the future.”
Coomer, a doctoral student in plant pathology with an emphasis on nematology and advised by Siddique, is working on her dissertation, "Plant Parasitic Nematode Effectors and Their Role in the Plant Defense Immune System."
Coomer, originally from the St. Louis, Mo., area, received two bachelor degrees--one in biology and the other in chemistry--in May 2020 from Concordia University, Seward, Neb., where she won the Outstanding Graduate Student in Biology Award. She served as a biology lab assistant and taught courses in general biology and microbiology.
As a biological science aide/intern, Coomer did undergraduate research in the Sorghum Unit of USDA's Agricultural Research Service. Lincoln, Neb. Her work included collecting, prepping and analyzing DNA, RNA and proteins to identify genes that contribute to an under- and over-expression of lignin in sorghum plants.
- Author: Kathy Keatley Garvey
“Most current control methods rely on chemical nematicides, but their use is increasingly limited due to environmental concerns,” wrote Siddique and colleague Clarissa Hiltl of the University of Bonn, Germany, in a newly published News and Views column, “New Allies to Fight Worms,” in the scientific journal Nature Plants.
In commenting on Washington State University (WSU) research published in the same edition, they wrote that the proposed alternative pest management strategy--naturally occurring molecules or plant elicitor peptides (Peps)—shows promise: “Engineering a naturally occurring rhizobacterium to deliver Peps to the plant root system offers a new opportunity in integrated pest management.”
It's better to build up the host plant's immune system rather than directly target the pathogen with chemical nematicides which “are highly toxic and have negative effects on the ecosystem,” declared Siddique, an assistant professor in the UC Davis Department of Entomology and Nematology.
“Plant-parasitic nematodes are among the world's most destructive plant pathogens, causing estimated annual losses of $8 billion to U.S. growers and of nearly $78 billion worldwide,” he said.
The root-knot nematode Meloidogyne chitwoodi is a noted pest of potato production in the Pacific Northwest. Idaho leads the nation in commercial potato production, followed by Washington. Oregon ranks fourth. California, which ranks eighth, grows potatoes year around due to its unique geography and climate.
In their article, Siddique and Hiltl analyzed research published by WSU Department of Pathology scientists Lei Zhang and Cynthia Gleason who demonstrated the effective use of Peps to combat root-knot nematodes in potato (Solanum tuberosum). The WSU scientists engineered a bacteria, Bacillus subtillis, to secrete the plant-defense elicitor peptide StPep1. Pre-treatment of potato roots “substantially reduced root galling, indicating that a bacterial secretion of a plant elicitor is an effective strategy for plant protection,” the Zhang-Gleason team wrote. (See article.)
Earlier scientists discovered that Peps could effectively manage nematodes in soybeans. Unlike the seed-grown soybeans, however, potatoes grow from small cubes of potatoes known as seed potatoes.
“Besides chemical nematicides, methods of nematode management include the use of crop rotation, microbial biocontrol agents, cover crops, trap crops, soil solarization, fumigation and resistant plant varieties,” wrote Siddique and Hiltl. “However, several of these strategies are not effective or available for all crops. Nematicides are highly toxic, and their use is strictly limited due to environmental concerns. Resistant plants are often ineffective or unavailable. Microbial biocontrol agents have produced inconsistent results. In this context, the current work provides a new opportunity to manage plant-parasitic nematodes by combining two progressive strategies: the use of plant elicitors to enhance crop resistance to pathogens and the use of B. subtilis to deliver.”
