12 October 2025
Jin-Peng Gao, Anil Kumar - Plant, Cell & Environment, 2025
The plant-specific GRAS protein family regulates a broad spectrum of developmental and physiological processes, including gibberellin signaling, shoot/root pattern, photomorphogenesis, and microbial symbiosis (Cheng et al. 2019). Unlike classical transcription factors, most GRAS proteins lack direct DNA-binding capacity, instead regulating gene expression through protein-protein interactions with other transcription factors (Jaiswal et al. 2022).
Arbuscular mycorrhizal (AM) symbiosis, which occurs in most land plants, enhances plant nutrient acquisition, such as phosphorus, nitrogen, and water, in exchange for photosynthetically derived carbon, thereby contributing to ecosystem stability (Luginbuehl and Oldroyd 2017; Rich et al. 2021). A hallmark of this symbiosis is the formation of highly branched arbuscules within root cortex cells, which depends on intricate transcriptional networks that reprogram colonized plant cells to accommodate and sustain these fungal structures (Luginbuehl and Oldroyd 2017; Pimprikar and Gutjahr 2018). Among GRAS-domain members, Required for Arbuscular Mycorrhization1 (RAM1) functions as a key transcriptional regulator for arbuscule development and function (Pimprikar et al. 2016; Xue et al. 2015). RAM1 orchestrates the expression of genes involved in lipid biosynthesis and transfer, as well as phosphate uptake, including RAM2, Stunted Arbuscule (STR), and Phosphate Transporter4 (PT4) (Park et al. 2015; Pimprikar et al. 2016; Xue et al. 2015). Despite its pivotal regulatory role, the molecular mechanism by which RAM1 activates transcription without a canonical DNA-binding domain has remained unresolved. A recent breakthrough study by Paries et al. (2025) revealed that RAM1 forms heteromeric complexes with a group of WRINKLED1 (WRI)-like transcription factors, including CBX1, WRI3, WRI5a, WRI5b, and WRI5c, which possess DNA-binding capacity. This RAM1-WRI module directly activates the expression of key symbiotic genes, effectively bridging the gap between GRAS-mediated protein-protein interaction and promoter-specific transcriptional regulation.
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