Blocking a Key Gene Shows How FACs Boost Nitrogen Metabolism

Jim Crocker
25th June, 2024

Blocking a Key Gene Shows How FACs Boost Nitrogen Metabolism

Disabling the gene for metabolizing fatty acid amino acid conjugates (FACs) in the agricultural pest Spodoptera litura (pictured) stunts larval growth by up to 40%, demonstrating this process is vital for the insect's ability to absorb nitrogen from its diet.

Photo adapted from: Stephen Thorpe / CC BY (Source)

Key Findings

  • Kyoto University studied the tobacco cutworm, a major pest in tropical and subtropical Asia
  • Disabling the FAC hydrolase gene in larvae led to 30% less nitrogen absorption from their diet
  • Mutant larvae weighed up to 40% less than normal larvae, highlighting the importance of FAC hydrolysis for growth
Spodoptera litura, commonly known as the tobacco cutworm, is a significant agricultural pest that has caused extensive damage to over 100 crops across tropical and subtropical Asia. This pest's ability to thrive on diverse plant species and resist various insecticides has been linked to its expanded gene families responsible for detecting and detoxifying plant secondary compounds[2]. Recent research conducted by Kyoto University has shed light on another aspect of this pest's biology, focusing on the role of fatty acid amino acid conjugates (FACs) in its nitrogen metabolism and overall growth[1]. FACs, such as volicitin and N-linolenoyl-L-glutamine, are compounds found in the regurgitant of Spodoptera exigua larvae. These compounds are known to trigger plants to release volatile chemicals that attract natural predators of the larvae, such as parasitic wasps. The regulation of FAC concentrations in the larvae involves enzymatic processes in their intestines, which include both the biosynthesis and hydrolysis of these compounds. FAC metabolism has been proposed to activate glutamine synthetase, an enzyme crucial for nitrogen metabolism in larvae. In their study, researchers at Kyoto University aimed to identify the genes encoding FAC hydrolases in Spodoptera litura by leveraging genomic data from related lepidopteran species where FAC hydrolases had been previously reported. Using CRISPR/Cas9 technology, they created strains of S. litura larvae with inactive FAC hydrolase genes to evaluate the importance of FAC hydrolysis on caterpillar performance. The results were telling. Larvae with inactive FAC hydrolase genes excreted FACs in their feces and absorbed 30% less nitrogen from their diet compared to wild-type caterpillars. This reduction in nitrogen absorption led to a significant decrease in body weight, with the mutant larvae weighing up to 40% less than their wild-type counterparts. This finding underscores the critical role of FAC hydrolysis in nitrogen metabolism and larval growth. This study builds on earlier findings about the role of plant-derived compounds and insect metabolism. For instance, previous research has shown that plants can respond to herbivore damage by producing specific volatile compounds that attract natural enemies of the herbivores[3]. The ability of Spodoptera litura to detoxify these plant compounds and survive despite these plant defenses is partially due to its expanded detoxification gene families[2]. Additionally, the study on gossypol, a toxic compound produced by cotton plants, revealed that consuming gossypol increased the levels of FACs in the feces of certain insect pests, suggesting a complex interaction between plant defenses and insect metabolism[4]. The Kyoto University study adds a new dimension to our understanding of these interactions by highlighting the importance of FAC hydrolysis in nitrogen metabolism and growth of S. litura larvae. By disrupting the FAC hydrolase gene, researchers were able to demonstrate that the hydrolysis of FACs is not just a detoxification process but also a critical metabolic pathway for nitrogen utilization in these pests. This research has significant implications for pest management strategies. Understanding the metabolic pathways that are crucial for the growth and survival of pests like S. litura can lead to the development of targeted interventions. For example, inhibitors of FAC hydrolase could potentially be used to reduce the nitrogen uptake efficiency of these pests, thereby stunting their growth and reducing their impact on crops. In summary, the study conducted by Kyoto University provides valuable insights into the metabolic processes that underpin the growth and survival of Spodoptera litura. By elucidating the role of FAC hydrolysis in nitrogen metabolism, this research opens up new avenues for developing targeted pest management strategies that could help mitigate the damage caused by this widespread agricultural pest.

GeneticsBiochemAnimal Science

References

Main Study

1) Knock-Out of ACY-1 Like Gene in Spodoptera litura Supports the Notion that FACs Improve Nitrogen Metabolism

Published 24th June, 2024

https://doi.org/10.1007/s10886-024-01512-y

Related Studies

2) Genomic adaptation to polyphagy and insecticides in a major East Asian noctuid pest.

https://doi.org/10.1038/s41559-017-0314-4

3) Differential induction of plant volatile biosynthesis in the lima bean by early and late intermediates of the octadecanoid-signaling pathway.

Journal: Plant physiology, Issue: Vol 121, Issue 1, Sep 1999

4) Consumption of gossypol increases fatty acid-amino acid conjugates in the cotton pests Helicoverpa armigera and Heliothis virescens.

https://doi.org/10.1002/arch.21843


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