AHG1–AFP interaction as a regulatory node in the ABA response during seed germination

Seed dormancy and germination are tightly regulated by complex signaling networks that integrate internal and external cues, including the endogenous phytohormone abscisic acid (ABA). ABA HYPERSENSITIVE GERMINATION 1 (AHG1), a group A type 2C protein phosphatase (PP2C), is thought to modulate the activity of transcription factors such as ABA INSENSITIVE 5 (ABI5) in seeds and during germination. AHG1 is regulated by DELAY OF GERMINATION 1 (DOG1), a key regulator of seed dormancy, through physical interaction. We previously reported that AHG1 also interacts with ABI FIVE BINDING PROTEIN 2 (AFP2), a member of the AFP family; however, the molecular basis of AHG1–AFP coordination has remained unclear. In this study, we show that AHG1 interacts with all AFP family members and that AFP3 binds AHG1 and ABI5 through adjacent but distinct amino acid residues within its C-domain, allowing simultaneous association with both proteins. In addition, AHG1 modulates the phosphorylation status of AFP3 at Ser60 in a DOG1-dependent manner, suggesting that DOG1–AHG1 regulates AFP3 post-translationally. Transcriptomic analyses of AHG1- or AFP3-overexpressing lines revealed that these factors are associated with the regulation of a shared set of ABA-responsive genes, including AFPs, and that AFP3 overexpression is predominantly associated with altered expression of genes involved in transcriptional regulation. Large-scale protein interaction analyses showed that AFPs interact with multiple classes of transcription factors, suggesting their involvement in diverse regulatory pathways, including ABA signaling. Together, these findings demonstrate that DOG1 regulates ABI5 function and modulates ABA responses, at least in part, by controlling AHG1-mediated dephosphorylation of AFPs.

This is the peer reviewed version of the following article: Nishimura, N., Ushiyama, S., Otagiri, M., Satoh, K., Suzuki, N., Irisa, T., Mitsuda, N., Umezawa, T., Nishimura, H., Nemoto, K., Tsuchiya, W., Yano, R., Sawasaki, T., Yamazaki, T. and Hirayama, T. (2026), AHG1–AFP interaction as a regulatory node in the ABA response during seed germination. Plant J, 127: e71081. https://doi.org/10.1111/tpj.71081, which has been published in final form at https://doi.org/10.1111/tpj.71081. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited

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