Transcriptional adapter ADA2 regulates yield and end‐use quality through liquid–liquid phase separation in wheat

Wheat (Triticum aestivum L.) yield and quality are critically influenced by starch and seed storage protein (SSP) content. In this study, we demonstrate that the transcriptional adapter ADA2 physically interacts with histone acetyltransferase GENERAL CONTROL NONDEREPRESSIBLE 5 (GCN5) and regulates starch synthesis and SSP content in wheat grains. In ada2 mutants, reduced H3K9ac enrichment was observed in the promoter regions of key starch synthesis genes and the SSP regulator NAC019 during endosperm development. This reduction leads to lower expression levels, resulting in decreased starch content, smaller grains, reduced yield, and poor gluten quality. We also found that ADA2 contains an intrinsically disordered region 2 (IDR2) that undergoes liquid-liquid phase separation (LLPS) and forms nuclear condensates. In vitro assays, the LLPS of ADA2 is affected by GCN5 through direct interaction with IDR2, and the ratio of their concentrations determines the behavior of phase-separated condensates and HAT activity. High levels of GCN5 can dissolve ADA2 aggregates, while excessive ADA2 recruits and sequesters GCN5 into co-aggregated droplets, with lower HAT activity. This potential dynamic regulatory mechanism may facilitate the efficient promotion of transcription by the ADA2-GCN5 complex in wheat. Finally, we identified an elite haplotype of ADA2-B Hap2, which is significantly associated with grain size and weight, highlighting its potential as a candidate gene for genetic improvement of wheat yield.