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3 recordsLinked to original sources
PubMed2026

Positive feedback loop between RAF12 and ABI5 reinforces ABA-mediated suppression of Arabidopsis seed germination.

ABA-INSENSITIVE 5 (ABI5) is a key transcriptional regulator mediating abscisic acid (ABA)-induced suppression of seed germination. However, the downstream regulatory network through which ABI5 exerts its function remains incompletely understood. Here, by integrating ChIP-seq and RNA-seq analyses, we identify RAF12, a member of the B2 Raf-like kinase subfamily, as a direct transcriptional target of ABI5. ABI5 binds to the RAF12 promoter and activates its expression. Loss-of-function raf12 mutants exhibit reduced sensitivity to ABA during seed germination, suggesting a negative regulatory role for RAF12 in this process. Conversely, RAF12 interacts with and phosphorylates ABI5, thereby enhancing its transcriptional activity. Further analysis showed that RAF12 regulates its own kinase activity through autophosphorylation. Mutations at its phosphorylation sites significantly weaken its ability to enhance ABI5's transcriptional activity. Together, these findings uncover a positive feedback loop wherein ABI5 transcriptionally activates RAF12, which in turn reinforces ABI5 activity through phosphorylation. This module may function in parallel with the canonical SnRK2s-ABI5-mediated ABA signaling cascade, offering new mechanistic insights into the fine-tuning of ABA responses during seed germination.

Arabidopsis↗
PubMed2025

Unraveling the molecular choreography of C3 to CAM transition in Mesembryanthemum crystallinum using phosphoproteomics.

Climate change and population growth threaten global freshwater resources and food security. Crassulacean acid metabolism (CAM) is a specialized photosynthetic adaptation that exhibits superior water use efficiency (WUE) compared to C3 and C4 photosynthesis. Mesembryanthemum crystallinum (common ice plant) is capable of shifting from C3 to CAM, making it a key model for investigating photosynthesis plasticity and its potential to enhance crop stress resilience. To date, the molecular mechanisms underlying this high-WUE photosynthetic transition remain largely unknown. Using mass spectrometry-based proteomics and phosphoproteomics, we quantified 4233 phosphopeptides containing 4758 phosphorylation sites, including the well-characterized Serine 11 of phosphoenolpyruvate carboxylase 1 (PEPC1). It is a critical phosphorylation site facilitating nocturnal CO2 fixation during CAM. Our analysis revealed many phosphorylation sites that exhibited similar diel patterns as the PEPC1 pS11, and they may be part of the regulatory network involved in CAM induction. Glycolysis/gluconeogenesis and carbon storage/breakdown modules exhibited extensive phosphorylation regulation, and vesicle trafficking could play a role in nocturnal carbon fixation. Furthermore, glycine-rich RNA-binding protein 7 (GRP7) in association with cold shock protein 1 (CSP1) emerged as a potential transcriptional switch for nocturnal stomatal opening. On the other hand, ABI5-binding protein 1 (AFP1) and oxidative stress 3 (OXS3)-activated ABA signaling, along with high CO2 signaling and suppressed blue light signaling, may contribute to diurnal stomatal closure. These findings shed light on the protein phosphorylation changes and provide valuable targets for functional characterization of their roles in CAM induction.

Mesembryanthemum↗
PubMed2026

Abscisic acid promotes RBOH-dependent reactive oxygen species production and lignin biosynthesis in pears via the PuABI5-PuMYB169 module.

Pear stone cell lignification, a critical determinant of fruit texture and quality, is regulated by developmental and environmental cues, with abscisic acid (ABA) playing a central role. However, the molecular mechanisms underlying its role in reactive oxygen species (ROS)-mediated lignification remain unclear. Here, we show that PuABI5, a key component in ABA signaling, directly combines with PuMYB169, the master regulator of stone cell lignification, to modulate ROS production and lignin biosynthesis in pear fruit. Exogenous application of ABA enhances H2O2 and lignin accumulation in both pear fruits and calli, and ABA-activated PuABI5 positively regulates stone cell lignification. We demonstrate that ABA-induced PuABI5 binds directly to the PuMYB169 promoter and activates its expression to promote the transcription of PuRBOHF and lignin-related genes, thereby enhancing ROS production and lignin accumulation. Notably, PuABI5 interacted with PuMYB169 to enhance the induction of PuRBOHF expression, leading to elevated levels of H2O2, which feedback to strengthen the interaction between PuABI5 and PuMYB169. Collectively, our findings elucidate that ABA induces ROS-mediated lignification of stone cells in pears by activating the PuABI5-PuMYB169 transcriptional module.

Lignin↗