- Author: Kathy Keatley Garvey
Today, during the 62nd annual international conference of the Society of Nematologists, being held July 9-14 in Columbus, Ohio, The Proceedings of the National Academy of Sciences (PNAS) published a UC Davis research team's important--and exciting--research paper on root-knot nematodes.
It's online at “Root-Knot Nematodes Produce Functional Mimics of Tyrosine-Sulfated Plant Peptides."
Basically, the researchers discovered that “both a harmful plant bacterium and a parasitic worm can mimic a plant peptide hormone to enhance their ability to infect plants.”
It's a joint project of nematologist Shahid Siddique, an associate professor in the Davis Department of Entomology and Nematology, and Siddique and UC Davis distinguished professor Pamela Ronald, a plant pathologist and geneticist in the Department of Plant Pathology and the Genome Center. They are the 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.
It's like hijacking plant development to facilitate parasitism, according to Siddique. “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.”
“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.
Plant-parasitic nematodes (PPNs) are among the most destructive plant pathogens, causing an annual economic loss of $8 billion to U.S. growers and more than $100 billion worldwide, the authors said.
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 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
The nematode collection featured mostly root-knot nematodes and Ascaris (roundworm) nematodes. The display included:
- 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
"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, he says. "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."
Nematologist Steve Nadler, professor and chair of the UC Davis Department of Entomology and Nematology, explains what a nematode is on this YouTube video that he presented at last year's UC Davis Biodiversity Museum Day. Due to COVID-19 precautions, the 2021 event was virtual, instead of in-person.
Visitors to the 2022 UC Davis Biodiversity Museum Day adhered to the Campus Ready guidelines, with masks required. Eleven museums or collections participated:
- Arboretum and Public Garden
- UC Davis Bee Haven
- Bohart Museum of Entomology
- Botanical Conservatory
- California Raptor Center
- Center for Plant Diversity
- Department of Anthropology Museum
- Museum of Wildlife and Fish Biology
- Nematode Collection
- Paleontology Collection
- Phaff Yeast Culture Collection
In addition, visitors could register for side trips to the Arboretum and Public Garden, Bee Haven and Phaff Yeast Culture Collection. The Botanical Conservatory opened its doors to visitors throughout the day.
Traditionally, the UC Davis Biodiversity Museum Day takes place the Saturday of Presidents' Weekend, and at the individual locations, noted organizer Tabatha Yang, education and outreach coordinator. This year it occurred at one site, exposition-style.
The campus is now gearing up for the 108th annual UC Davis Picnic Day, set April 23 and themed "Rediscovering Tomorrow." The free public event is the first, in-person Picnic Day in two years.
- Author: Kathy Keatley Garvey
You're not thinking of root-knot nematodes, major pests of potatoes.
But potato growers and nematologists are.
So are the editors of the scientific journal, Nature Plants. Their current edition showcases research on root-knot nematodes by Washington State University (WSU) scientists Lei Zhang and Cynthia Gleason, and a commentary by UC Davis nematologist Shahid Siddique and colleague Clarissa Hiltl of the University of Bonn, Germany.
“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," according to Siddique, an assistant professor in the UC Davis Department of Entomology and Nematology.
“Most current control methods rely on chemical nematicides, but their use is increasingly limited due to environmental concerns," Siddique and Hiltl wrote in their News and Views column, New Allies to Fight Worms.
They commented that the WSU scientists' 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," Siddique told us.
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.
The WSU scientists demonstrated the effective use of Peps to combat root-knot nematodes in potato (Solanum tuberosum). They engineered a bacteria, Bacillus subtillis, to secrete the plant-defense elicitor peptide StPep1. They wrote that 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." (See article.)
“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.”
According to the UC Statewide Integrated Pest Management Program (UC IPM), root-knot nematodes "usually cause distinctive swellings, called galls, on the roots of affected plants. Infestations of these nematodes are fairly easy to recognize; dig up a few plants with symptoms, wash or gently tap the soil from the roots, and examine the roots for galls. The nematodes feed and develop within the galls, which can grow as large as 1 inch in diameter on some plants but usually are much smaller."
"Nematodes are too small to see without a microscope," UC IPM points out. "Often you become aware of a nematode problem by finding galled roots on a previous crop. However, you also can use a simple bioassay to detect root knot nematodes in garden soil. Melons seeded in pots in moist soil collected from the garden will develop visible galls on the roots in about 3 weeks when pots are kept at about 80ºF if root knot nematodes are present. As a comparison, melons planted in heat-sterilized soil won't develop galls."
Stay tuned.