Microsatellite expansion redirects chromatin modifiers to confer insect resistance to Bt bioinsecticides.

A tetranucleotide (ATGT) microsatellite expansion in the ABCC2 promoter epigenetically silences ABCC2 and confers Bt Cry1Ac resistance in Plutella xylostella (L.).

• Why it matters: Adaptive gene regulation by mutable microsatellites in insects is poorly understood, limiting insight into how rapid xenobiotic-resistance evolution is controlled.
• What they did: In Cry1Ac-resistant strains, long (≥27 units) ATGT repeats preferentially recruit the histone methyltransferase E(z) to promote H3K27me2/3 deposition, while short repeats in susceptible strains maintain open chromatin via Tip60-mediated H4K5 acetylation.
• The result: Repeat expansion alone is sufficient to repress ABCC2 and confer Bt resistance, and repeat length, chromatin state, and phenotypes partially revert under relaxed selection.