- Author: Kathy Keatley Garvey
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.
"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.”