Genomic Duplication and Auxin Manipulation Enable Gall Aphids to Reprogram Host Plants
Researchers have identified the molecular mechanism by which the horned gall aphid Schlechtendalia chinensis induces gall formation in its host tree, tracing it to a salivary enzyme that activates plant growth hormones. The study combined chromosome-level genome sequencing of both the aphid and its host with proteomics, metabolomics, and functional experiments. The findings illuminate how genomic duplication can drive the evolution of parasitic traits that manipulate host physiology.
A new study published on bioRxiv reports chromosome-level genome assemblies for the horned gall aphid Schlechtendalia chinensis and its host, the Chinese sumac Rhus chinensis, shedding light on how insect galls — complex plant structures induced by parasites — are formed at the molecular level. The aphid's genome features an unusually large chromosome 1 (93.61 Mb) that harbors a disproportionate share of the genome's genes and over 70% of its segmental duplications, suggesting this region is a hotspot for evolutionary innovation. Within this genomic context, the researchers identified a salivary enzyme called ACY1, belonging to the M20 family, which functions as an auxin-conjugate hydrolase. ACY1 cleaves inactive, stored forms of the plant hormone auxin from their amino acid conjugates, releasing active auxin and elevating its local concentration in host tissue. This hormonal manipulation reprograms plant cell development, driving the formation of galls that serve as the aphid's habitat and food source. Loss- and gain-of-function experiments confirmed ACY1's causal role in this process. The authors propose that concentrated genomic duplication on chromosome 1 provided the raw material for evolving this effector, offering a broader principle for understanding how parasitic traits emerge.
What's missing
It remains unclear whether ACY1-like mechanisms are conserved across other gall-forming insects or are unique to S. chinensis. The study does not fully address how the aphid regulates ACY1 delivery to specific host tissues, nor whether host plants have evolved counter-defenses against this enzymatic manipulation.
What different sources said
- bioRxivCenter
Chromosome gigantism and auxin deconjugation underpin gall induction in a horned gall aphid
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