UC Davis plant pathologist Shahid Masood Siddique

It's somewhat like that when plant-parasitic nematodes (microscopic round worms) play “chemical hide and seek” with their plant host, says plant pathologist  Shahid Masood Siddique, an assistant professor in the UC Davis Department of Entomology and Nematology.

“The success of plant-parasitic nematodes depends on their ability to locate a suitable host in the soil,” says Siddique, corresponding author of the newly published Spotlight article, “Chemical Hide and Seek: Nematode's Journey to Its Plant Host,” in the journal Molecular Plant.

Nematodes can be deadly to plants, not only because of the direct damage they cause (they extract water and nutrients from their hosts such as wheat, soybeans, sugar beets, citrus, coconut, corn, peanuts, potato, rice, cotton and bananas) but the role of some species as virus vectors.

“Plant-parasitic nematodes are among the most destructive agricultural pests, causing more than $100 billion in losses per year in the United States,” Siddique said, noting that nematodes are especially damaging to potato, soybean and wheat crops.

Although the success of nematodes depends on their ability to locate a suitable host in the soil, what attracts them to their host “has largely remained unknown,” wrote the four-member UC Davis team of Siddique, Natalie Hamada, Henok Zemene Yimer and Valerie Williams. “Recent studies have revealed that host-seeking by nematodes is a complex process that involves multiple stages in the interaction.”

“Most damage is caused by a small group of root-infecting sedentary endoparasitic nematodes including cyst nematodes and root-knot nematodes (RKNs),” the team of UC Davis researchers wrote in their abstract. “Second stage juveniles (J2s) of plant-parasitic nematodes hatch from eggs into the soil and localize to the roots of host plants. The success of these non-feeding J2s depends on their ability to locate and infect a suitable host.”

For eight decades, scientists have researched the attraction of plant-parasitic nematodes to the host root, ever since the pioneering Maurice Blood Linford (1901-1960) of the University of Illinois, Urbana, Ill., observed in 1939 that the larvae of root-knot nematodes congregate in the cell elongation region behind the root cap.

“Both volatile and soluble components in the rhizosphere have been shown to influence nematode movement,” the UC Davis researchers wrote. “Methyl salicylate, a volatile chemical root signal, has been demonstrated to be a strong root attractant for RKN towards several Solanaceous plants (nightshade family). The non-volatile tomato root exudate quercetin was shown to elicit concentration dependent attraction or repulsion effect against Meloidogyne incognita to host root. Three recent studies have revealed that the recognition of and response to hosts by infective juveniles is a complex process that involves multiple stages in the interaction.”

Siddique 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.”  

Bruce Hammock in 1980

Bruce Hammock today

Entomologist Marlin Rice, a past president of the Entomological Society of America (ESA), penned the piece, titled "Bruce D. Hammock: Science Should Be Fun!"

Wrote Rice: "Bruce D. Hammock is widely known for his groundbreaking research in insect physiology, toxicology, pharmacology, and experimental therapeutics. Early contributions were in fundamental regulatory biology, development of both small molecules and recombinant viruses as environmentally friendly pesticides, and the application of accelerator mass spectrometry to biological science. His laboratory pioneered the use of immunoassay for the analysis of human and environmental exposure to pesticides and other contaminants.His laboratory provides graduate training that is diverse in disciplines and research areas. He recently formed a company, EicOsis, to develop an orally active non-addictive drug for inflammatory and neuropathic pain for humans and companion animals."

Hammock, who joined the UC Davis faculty in 1980 from UC Riverside, has directed the UC Davis Superfund Research Program (funded by the National Institutes of Health's National Institute of Environmental Health Sciences) for nearly four decades. He is a member of the National Academy of Sciences, and a fellow of the National Academy of Inventors and ESA.

A native of Little Rock, Ark., Bruce received his bachelor's degree in entomology (with minors in zoology and chemistry) magna cum laude from Louisiana State University, Baton Rouge, in 1969. He received his doctorate in entomology-toxicology from UC Berkeley in 1973 with John Casida at UC Berkeley. Hammock served as a public health medical officer with the U.S. Army Academy of Health Science, San Antonio, and as a postdoctoral fellow at the Rockefeller Foundation, Department of Biology, Northwestern University, Evanston, Ill.

Read the feature story here.

Some Related Links:

• Bruce Hammock and EicOsis, Innovator of the Year
• Bruce Hammock Receives $6 Million Grant
• Bruce Hammock Water Balloon Battle: 15 Minutes of Aim
• Research Could Lead to Drug to Prevent or Reduce Autism, Schizophrenia 
• Hammock Lab Union Draws 100 Scientists from 10 Countries
• Bruce Hammock: Scientist Extraordinaire

(Editor's Note: Thanks to Lisa Junker, ESA's director of publications, communications and marketing, who reached out to "our publishers at Oxford" to grant free community access to this feature story in American Entomologist)

Emily Meineke, assistant professor of urban landscape entomology

Before accepting her UC Davis appointment, Meineke served as a National Science Foundation postdoctoral fellow at the Harvard University Herbaria, where she studied how urbanization and climate change have affected plant-insect relationships worldwide over the past 100-plus years.

A native of Greenville, N.C., Emily received her bachelor of science degree in environmental science, with a minor in biology, in 2008 from the University of North Carolina, Chapel Hill, and then went on to obtain her doctorate in entomology in 2016 from North Carolina State University. Advised by Steven Frank and co-advisor Robert Dunn, she completed her dissertation on  "Understanding the Consequences of Urban Warming for Street Trees and Their Insect Pests."

Some questions:

1. Please expand on the kind of research you do.

"Insects have eaten plants for around 400 million years. These interactions have given rise to most of terrestrial biodiversity. Over the past 12,000 years, humans have disrupted plant-herbivore relationships by building cities, domesticating crops, and changing the global climate."

"I investigate these disruptions, focusing on species that are of cultural importance, such as street trees, crops, crop wild relatives, and plants that support rare insect species. My work combines experiments, observations, citizen science, and biological collections to address key hypotheses in ecology."

2. What do you like best about your work?

"I love discovery, the moment when you as a scientist know something that no one else knows. I love passing that experience on to students. I also love that my work reflects my personal values. Biodiversity is critically important, and the fact that I get to study it for a living is a real privilege."

3. How did you get interested in entomology? Can you recall an occasion that sparked your interest? 

"I have no idea, honestly. I never had an insect collection as a kid, and I was equally interested in all living things, from my family's pets to the toads that lived in my backyard. At some point after my undergraduate education, I realized that insects are both invisible to us most of the time and are incredibly present in our lives and imaginations. Ecologically, because they are small in size, they can seem unimportant because we are biased to think creatures our size or larger are important, but insects are really the little things that run the world."

4. How would you describe yourself?

"I'm a pretty serious person who is always working to be more light-hearted. I am both easily discouraged and tenacious. I would describe myself as creative and am drawn to diversity in all forms."

5. What drew you to UC Davis?

"When I visited, I got the feeling that UC Davis encourages creativity while valuing research that produces real solutions. When I interviewed here, I felt I would be able to be myself as a researcher and that my fellow faculty would support that. On top of that, UC Davis is such an established institution with great resources in a beautiful part of the world. I can't think of a better place to be."

6. What do you like to do in your leisure time?

"All I really ever want to do is eat and spend time with people I love. 'People' includes my two dogs, who rule the house."

9. What would people be surprised to know about you?

"I have a hidden talent. I can make very realistic cat meows. I can fool anyone's cat and most humans."

Other
In addition to her NSF Postdoctoral Research Fellowship, she received a number of other honors, including Student Appreciation for the Biology of Insect Pests Award; Garden Club of America Urban Forestry Fellowship; and the EPA Science to Achieve Results (STAR) Fellowship.

A member of the Entomological Society of America (ESA), Ecological Society of America and the Botanical Society of America, she has presented talks across the continent, as well as in Finland, Spain, Canada, France and Denmark. She delivered a presentation at the 2016 International Congress of Entomology in Orland, Fla., and at ESA's national and regional meetings.

Meineke has published her work in Ecological Monographs, Ecology and Evolution, Journal of Applied Ecology, and the Journal of Urban Ecology, among others.

The Boston Globe featured her research in a news story published Oct 11, 2018: "Rising Temperatures May Cause Insects to Eat More Plants, Harvard Study Says"

Nature journal featured her in a research highlights piece, "Warmer Forests Store Less Carbon," published Oct. 12, 2016

Los Angeles Times spotlighted her in its Oct. 6, 2016 piece, "As Cities Get Warmer, These Trees Lose Some of their Ability to Take Carbon Out of the Atmosphere."

Contact:
ekmeineke@ucdavis.edu.

Parents often try to predict the gender of their offspring, but is it possible to predict the sex of a cyst or sexually dimorphic nematode?

Yes, says plant nematologist Shahid Masood Siddique of the UC Davis Department of Entomology and Nematology,  who helped develop and validate a strategy to predict the sex of cyst nematodes (round worms) in roots of a mustard family plant in the early stages of infestation.

The research paper, "Host Factors Influence the Sex of Nematodes Parasitizing Roots of Arabidopsis thaliana," published in a recent edition of the journal Plant, Cell and Environment, zeroes in on nematodes parasitizing a small flowering plant widely used in plant biology and known as "mouse-ear cress." Arabidopsis is a member of the mustard (Brassicaceae) family, which includes cabbage and radish. A native of Eurasia and Africa, mouse-ear cress is found throughout much of the United States and Canada.

"We identified the host genes and factors that influence environmental sexual determination of plant parasitic nematodes," said Siddique, the senior author of the paper and an assistant professor at UC Davis. He played a key role in designing and performing the research well as the written work.

The seven-member team, led by Florian Grundler of the University of Bonn, Germany, found that the nematodes that developed at the fastest rate during the first four to 5 days became females, "whereas those that grew slower became mainly males."

"Interestingly, a study by Müller et al. (1981) on comparative food consumption by male and female juveniles from roots of Brassica napus found that females consume about 29 times more food than males," the researchers wrote. "Based on our data and previous literature, we concluded that the difference in food consumption leads to the difference in body volume between the sexes."

The team also included scientists from Germany, Poland, and Pakistan. A DAAD grant from Germany funded the research.

The abstract:

"Plant-parasitic cyst nematodes induce hypermetabolic syncytial nurse cells in the roots of their host plants. Syncytia are their only food source. Cyst nematodes are sexually dimorphic, with their differentiation into male or female strongly influenced by host environmental conditions. Under favourable conditions with plenty of nutrients, more females develop, whereas mainly male nematodes develop under adverse conditions such as in resistant plants. Here, we developed and validated a method to predict the sex of beet cyst nematode (Heterodera schachtii) during the early stages of its parasitism in the host plant Arabidopsis thaliana. We collected root segments containing male-associated syncytia (MAS) or female-associated syncytia (FAS), isolated syncytial cells by laser microdissection, and performed a comparative transcriptome analysis. Genes belonging to categories of defence, nutrient deficiency, and nutrient starvation were over-represented in MAS as compared with FAS. Conversely, gene categories related to metabolism, modification, and biosynthesis of cell walls were over-represented in FAS. We used β-glucuronidase analysis, qRT-PCR, and loss-of-function mutants to characterize FAS- and MAS-specific candidate genes. Our results demonstrate that various plant-based factors, including immune response, nutrient availability, and structural modifications, influence the sexual fate of the cyst nematodes."

Siddique, who joined the UC Davis faculty in March, 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."

Plant-parasitic nematodes are microscopic worms that extract water and nutrients from such host plants as wheat, soybeans, sugar beets and bananas. “They're one of the most destructive agricultural pests,” Siddique says. “The agricultural losses due to plant-parasitic nematodes reach an estimated $80 billion. The high impact of plant parasitic nematodes in economically important crops is not only due to the direct damage but also because of the role of some species as virus vectors.”

Related Link:

Meet Shahid Masood Siddique