By Rahul Kumar
Insects account for a major proportion of invasive alien species in India. They incur a huge economic cost to the country. Fall armyworm (Spodoptera frugiperda) is one of the most notorious and fast spreading invasive alien species in India. It is known that the fall armyworm (FAW) infests 353 different plant types from 76 different plant families. Larvae mostly harm crops by eating leaf tissue, but they can also bore into other growing parts of the plant. It came to India from America through Africa. The first case was reported from India in 2018. Ever since it has spread over all parts of India, including the Himalayas, in just one year.
Insecticides are the most popular method of control of invasive insects like FAW. But indiscriminate overuse of insecticides often leads to death of beneficial species and development of resistance against the insecticide in the target insect pest. Many insecticides are also poisonous to other life forms and deleteriously affect the food chain. Issues of biomagnification and bioaccumulation have been observed with many insecticides. Soil and water contamination is yet another issue attributed to overuse of insecticides. Therefore, a safer and sustainable method of control of invasive insect species is required. This method should also be cost effective and farmer friendly. Recently, a group of Indian scientists have developed a CRISPR-Cas9 based precision‐guided sterile insect technique for control of FAW.
This method is based on editing an important gene named tssk2 (testis‐specific serine/threonine kinases) in male FAW. This gene is involved in the process of spermatogenesis and is essential for the fertility of the moth as found by the scientists. It is associated with post‐meiotic chromatin remodelling in insects. This gene is conserved across different lepidopteran taxa and exhibits high expression levels in testis. In this study, this gene was cloned from the testis of FAW male. In silico studies were conducted to understand the structure of its protein product and to identify the potential target site for designing guide RNA for gene editing. It was edited by microinjecting CRISPR-Cas9 ribonucleo-protein complex containing gRNA into G0 eggs. CRISPR (clustered regularly interspaced short palindromic repeat) technology has already been used for precise gene editing and epigenome modifications in many biological systems. CRISPR proteins function by recruiting a modified Cas (CRISPR-associated) protein, which is a sequence specific endonuclease, to target sequences using a short stretch of RNA called guide RNA (gRNA). Cas9 is the most widely used Cas with CRISPR.
Figure: Schematic representation of CRISPR-Cas9 based precision‐guided sterile insect technique using male tssk2 gene editing for control of fall armyworm.
After performing gene editing, male adult moths with edited tssk2 gene were screened using DNA sequencing data and crossed with wildtype females. The mutated proteins resulting from the edited tssk2 gene were also analyzed in silico using homology modelling and Ramachandra plots for resulting structural deformities. The resulting edited males were found to be sterile but capable of undergoing normal mating process. The females are born normal but their mating with these sterile male mutants leads to gradual reduction of FAW population over time. This study presents an effective and sustainable method for genetic pest management of FAW. As tssk2 is a highly conserved gene across different lepidopteran taxa, a similar approach can be used for the management of other lepidopteran insect pests.
For more details, please refer:
Anu, C. N., Ashok, K., Bhargava, C. N., Dhawane, Y., Manamohan, M., Jha, G. K., & Asokan, R. (2024). CRISPR/Cas9 mediated validation of spermatogenesis‐related gene, tssk2 as a component of genetic pest management of fall armyworm, Spodoptera frugiperda (JE Smith)(Lepidoptera: Noctuidae). Archives of Insect Biochemistry and Physiology, 116(1), e22121. https://doi.org/10.1002/arch.22121
Rahul Kumar is one of the Associate Editors of Indian Entomologist. He is presently working as Assistant Professor and Head of the Department of Zoology, Sheodeni Sao College (Magadh University), Kaler-824127, India. He is trained in Molecular Biology (eukaryotic gene regulation) from JNU, New Delhi; Nanotechnology (nano-therapeutics and nano-diagnostics) from AIIMS, New Delhi; Science Education (teaching and learning) from NCERT, New Delhi and Arthropod Taxonomy (spiders and insects) from ICAR-IARI, New Delhi. His current areas of research are mimicry and other aspects of arthropod behaviour, evolution of mimicry, novel approaches like application of nanotechnology in modern arthropod systematics, and chemical ecology of arthropods. He can be contacted at rahuldayanand33@gmail.com