Microbiome and plant cell transformation trigger insect gall induction in cassava

Area of Science:

• Plant-insect interactions
• Molecular biology
• Microbiome research

Background:

• Insect galls are complex plant structures resulting from insect manipulation, but the induction mechanism remains unclear.
• Understanding gall formation is key to deciphering intricate plant-insect relationships.

Purpose of the Study:

• To elucidate the induction mechanism of insect galls using cassava and the gall midge *Iatrophobia brasiliensis* as a model.
• To test the hypothesis that gall cells are genetically transformed by insect-vectored bacteria.

Main Methods:

• Utilized PCR-based molecular markers and deep metagenomic sequencing to analyze the gall microbiome.
• Employed shotgun sequencing to differentiate foreign DNA from the host plant genome.
• Conducted inoculation assays with *Rhodococcus* bacteria to induce gall-like structures.

Main Results:

• Identified bacterial DNA sequences in cassava galls, including genes related to transcription regulation (CadR), metal transport (cadA, arsA), and nitrate transport (nrtB).
• Discovered a DNA fragment associated with the ubiquitin-like gene E2, potentially involved in gall induction.
• Demonstrated that gall development is driven by microbiome enrichment and endophyte acquisition, with *Rhodococcus* inducing gall-like structures.

Conclusions:

• Insect-induced gall formation in cassava requires both endophytic microbiome modification and genetic transformation of plant cells.
• Bacterially mediated genetic transformation of plant cells may be a widespread mechanism for gall induction across different plant species.