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A promising gene to control the reproductive potential of aphids

In the context of reducing pesticide use, the management of crop pest insects necessitates unceasing efforts to develop innovative control strategies. In the pea aphid, RNA interference technology (RNAi) has enabled inactivation of the PAH (PhenylAlanine Hydroxylase) gene which is essential for embryonic development of the insect.

Pea aphids Acyrthosiphon pisum (green body) on faba bean (Vicia faba). Founder with young larval stages. The eyes (points in dark red) of the embryos from the parthenogenetic reproduction are visible by transparency in the abdomen of the female.. © Inra, Federica Calevro

The importance of better understanding aphid biology

Because of their sap-sucking behaviour (uptake of nutrients from sap) and their ability to spread viral diseases, aphids are major pests that cause enormous crop losses each year. Their invasive nature is based on their reproductive potential, either sexually or by parthenogenesis (the latter allowing females to produce offspring of 80 further females within a few days without the need for fertilisation).  Strategies to control aphids have hitherto been based on the massive use of insecticides, against which the insects have developed resistance. Regulations on reducing the use of chemical agents have stimulated the discovery of alternative methods, thus requiring a clearer understanding of the biology of these insects. Recent availability of the genome of the pea aphid (Acyrthosiphon pisum) has led to this species becoming a model for the discovery of biological functions that could be targeted by these new approaches.

The physiological role of phenylalanine hydroxylase in insects

Phenylalanine hydroxylase is an important enzyme which catalyses the conversion of phenylalanine into tyrosine. In insects, this enzyme is an essential component in the metabolism of pigmentation, involved notably in the changes to cuticle colour and sclerotization that permit a reconstruction of internal structures during metamorphosis. However, its role in the embryonic development of insects was previously unknown. For the first time, our study has enabled us to characterise the role of the PAH gene coding for phenylalanine hydroxylase in the physiology of heterometabolic insects (pterygote insects whose juveniles resemble adults) and to identify tyrosine biosynthesis as a key metabolic pathway for the parthenogenetic development of A. pisum.

PAH: a metabolic gene that is essential for the embryonic development of aphids

By inactivating this gene with RNAi in parthenogenetic females, the scientists succeeded in significantly reducing the lifespan and fecundity of the aphids (nearly 40% fewer offspring per female). Other harmful effects were also observed in newly laid nymphs, such as major morphological defects: malformation of the cuticle and eyes, an absence of or alterations to appendages such as antennae, feet or labium, and a significant reduction in size. Furthermore, the affected nymphs presented with tyrosine deficiency and an accumulation of its precursor, phenylalanine, thus confirming the disruption of PAH gene activity by RNAi.

This research finding offers promising perspectives for crop protection. Targeting the PAH gene in aphids by spraying with interfering RNA or using other methods to inhibit this gene (e.g. the use of enzymatic inhibitors) would enable elimination of most of the population present, and affect both the fertility of survivors and development of their offspring. The gene sequence is sufficiently divergent to enable the specific targeting of aphids and avoid any off-target effects on other organisms, and notably on beneficial insects.

 
A partnership is currently being organised with the company Globachem (Sint-Truiden, Belgium) and the laboratory VIB-KU (Belgium) to develop a crop protection method that uses the inactivation of PAH and other target genes.

Contact(s)
Scientific contact(s):

  • Federica Calevro INRA/INSA Lyon Joint Research Unit for Functional Biology, Insects and Interactions (UMR 0203, BF2i), INSA Lyon, 20 Avenue Albert Einstein, 69621 VILLEURBANNE CEDEX
Associated Division(s):
Plant Health and Environment
Associated Centre(s):
Auvergne Rhône-Alpes

Find out more

  • Simonet P., Gaget K., Parisot N., Duport G., Rey M., Febvay G., Charles H., Callaerts P., Colella S., Calevro F. (2016) Disruption of phenylalanine hydroxylase reduces adult lifespan and fecundity, and impairs embryonic development in parthenogenetic pea aphids. Scientific Reports. 6, 34321; doi: 10.1038/ srep34321 (2016).
  • Sapountzis P., Duport G., Balmand S., Gaget K., Jaubert-Possamai S., Febvay G., Charles H., Rahbé Y., Colella S., Calevro F. (2014) New insight into the RNA interference response against cathepsin-L gene in the pea aphid, Acyrthosiphon pisum: Molting or gut phenotypes specifically induced by injection or feeding treatments. Insect Biochemistry and Molecular Biology doi: 10.1016/j.ibmb.2014.05.005.