# ADA2 Forms Nuclear Condensates with GCN5 and ATP‐Citrate Lyase (ACL) to Modulate H3K9 Acetylation at Genes Functioning in Rice Meristems

## TL;DR

This study reveals how a rice protein complex boosts gene activity in plant growth areas by forming nuclear condensates that increase acetyl-CoA for histone acetylation.

## Contribution

ADA2's intrinsically disordered region and its role in forming a GAA complex with GCN5 and ACL to modulate histone acetylation in rice meristems is newly identified.

## Key findings

- ADA2 forms nuclear condensates with GCN5 and ACL to enrich acetyl-CoA and promote histone H3K9 acetylation.
- Knockout of ADA2, GCN5, or ACL reduces root meristem size and branch primordia numbers in rice.
- The GAA complex facilitates histone acetylation at genes essential for rice meristem development.

## Abstract

SAGA (Spt‐Ada‐Gcn5 acetyltransferase) is a highly conserved histone acetyltransferase (HAT) complex in eukaryotes, playing a crucial role in regulating gene transcription during development. The complex consists of two core components: GCN5, the HAT subunit, and ADA2, which primarily functions as an adaptor and enhances the complex HAT activity. Beyond its well‐established roles, it is discovered in this work that ADA2 in rice possesses a broadly existing intrinsically disordered region (IDR) that directs the formation of nuclear condensates. Moreover, ADA2 is found to interact with a subunit of ATP‐citrate lyase (ACL), an enzyme that produces acetyl‐CoA, leading to the formation of a GCN5‐ADA2‐ACL (GAA) complex. ADA2 promotes the condensation of both GCN5 and ACL in vivo. Within these condensates, ACL contributes to the production and enrichment of acetyl‐CoA, thereby promoting histone acetylation. Genetic evidence showed that knock‐out or suppression of these genes led to similarly diminished root meristem zone sizes and reduced branch primordia numbers, accompanied by significant reductions in genomic H3K9 acetylation and transcriptional attenuation of essential genes for meristem function. In summary, the findings unveil a novel mechanism of HAT action by forming phase separation to enrich acetyl‐CoA within nuclear puncta, facilitating histone acetylation at target genes essential for meristem development.

This study unveils a novel GAA (GCN5‐ADA2‐ACL) complex that forms nuclear condensates to boost local acetyl‐CoA, facilitating histone acetylation and gene transcription in rice meristems. The research underscores the role of ADA2's disordered region in complex condensation and ACL's role in acetyl‐CoA production. The findings offer key insights into the mechanisms by which the histone acetylation complex works in plant meristems.