Auxin, indole-3-acetic acid (IAA), is a key phytohormone with diverse morphogenic roles in land plants, but its function and transport mechanisms in algae remain poorly understood. We therefore aimed to explore the role of IAA in a complex, streptophyte algae Chara braunii. Here, we described novel responses of C. braunii to IAA and characterized two homologs of PIN auxin efflux carriers: CbPINa and CbPINc. We determined their localization in C. braunii using epitope-specific antibodies and tested their function in heterologous land plant models. Further, using phosphoproteomic analysis, we identified IAA-induced phosphorylation events. The thallus regeneration assay showed that IAA promotes thallus elongation and side branch development. Immunolocalization of CbPINa and CbPINc confirmed their presence on the plasma membrane of vegetative and generative cells of C. braunii. However, functional assays in tobacco BY-2 cells demonstrated that CbPINa affects auxin transport, whereas CbPINc does not. The IAA is effective in the acceleration of cytoplasmic streaming and the phosphorylation of evolutionary conserved targets such as homolog of RAF-like kinase. These findings suggest that, although canonical PIN-mediated auxin transport mechanisms might not be fully conserved in Chara, IAA is involved in morphogenesis and fast signaling processes.

• Klíčová slova
• Chara, auxin transport, indole‐3‐acetic acid, plant evolution, streptophytes,
• MeSH
• biologický transport účinky léků   MeSH
• buněčná membrána metabolismus   účinky léků   MeSH
• Chara * metabolismus   účinky léků   MeSH
• fosforylace účinky léků   MeSH
• kyseliny indoloctové * metabolismus   farmakologie   MeSH
• membránové transportní proteiny * metabolismus   MeSH
• rostlinné proteiny * metabolismus   MeSH
• tabák metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• indoleacetic acid MeSH Prohlížeč
• kyseliny indoloctové * MeSH
• membránové transportní proteiny * MeSH
• rostlinné proteiny * MeSH

Aux/IAA proteins are well-known as key components of the nuclear auxin signaling pathway, repressing gene transcription when present and enabling gene activation upon their degradation. In this review, we explore the additional roles of Aux/IAA proteins in the known auxin perception pathways-the TIR1/AFBs nuclear as well as in the emerging cytoplasmic and apoplastic pathways. We summarize recent advances in understanding the regulation of Aux/IAA protein stability at the post-translational level, a critical factor in auxin-regulated transcriptional output. We further highlight the roles of auxin-nondegradable non-canonical Aux/IAAs in auxin-mediated transcription and their involvement in apoplastic auxin signalling. Additionally, we discuss the importance of Aux/IAAs for the adenylate cyclase activity of TIR1/AFB receptors and speculate on their involvement in the cytoplasmic auxin pathway. Using Arabidopsis root as a model, this work underscores the central role of Aux/IAA proteins in mediating auxin-driven developmental processes and environmental responses. Key questions for future research are proposed to further unravel the dynamic roles of Aux/IAAs in auxin signaling networks.

• MeSH
• Arabidopsis * metabolismus   genetika   MeSH
• F-box proteiny metabolismus   genetika   MeSH
• kořeny rostlin metabolismus   MeSH
• kyseliny indoloctové * metabolismus   MeSH
• proteiny huseníčku * metabolismus   genetika   MeSH
• receptory buněčného povrchu metabolismus   genetika   MeSH
• regulace genové exprese u rostlin MeSH
• regulátory růstu rostlin * metabolismus   MeSH
• rostlinné proteiny * metabolismus   genetika   MeSH
• signální transdukce MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• F-box proteiny MeSH
• kyseliny indoloctové * MeSH
• proteiny huseníčku * MeSH
• receptory buněčného povrchu MeSH
• regulátory růstu rostlin * MeSH
• rostlinné proteiny * MeSH

The plant-signaling molecule auxin triggers fast and slow cellular responses across land plants and algae. The nuclear auxin pathway mediates gene expression and controls growth and development in land plants, but this pathway is absent from algal sister groups. Several components of rapid responses have been identified in Arabidopsis, but it is unknown if these are part of a conserved mechanism. We recently identified a fast, proteome-wide phosphorylation response to auxin. Here, we show that this response occurs across 5 land plant and algal species and converges on a core group of shared targets. We found conserved rapid physiological responses to auxin in the same species and identified rapidly accelerated fibrosarcoma (RAF)-like protein kinases as central mediators of auxin-triggered phosphorylation across species. Genetic analysis connects this kinase to both auxin-triggered protein phosphorylation and rapid cellular response, thus identifying an ancient mechanism for fast auxin responses in the green lineage.

• Klíčová slova
• RAF kinase, auxin, plant evolution, protein phosphorylation,
• MeSH
• Arabidopsis genetika   metabolismus   MeSH
• bílkoviny řas metabolismus   MeSH
• fosforylace MeSH
• kyseliny indoloctové metabolismus   MeSH
• proteinkinasy metabolismus   MeSH
• regulace genové exprese u rostlin MeSH
• rostlinné proteiny metabolismus   MeSH
• rostliny metabolismus   MeSH
• signální transdukce * MeSH
• vyšší rostliny * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bílkoviny řas MeSH
• kyseliny indoloctové MeSH
• proteinkinasy MeSH
• rostlinné proteiny MeSH

Plant roots navigate in the soil environment following the gravity vector. Cell divisions in the meristem and rapid cell growth in the elongation zone propel the root tips through the soil. Actively elongating cells acidify their apoplast to enable cell wall extension by the activity of plasma membrane AHA H+-ATPases. The phytohormone auxin, central regulator of gravitropic response and root development, inhibits root cell growth, likely by rising the pH of the apoplast. However, the role of auxin in the regulation of the apoplastic pH gradient along the root tip is unclear. Here, we show, by using an improved method for visualization and quantification of root surface pH, that the Arabidopsis thaliana root surface pH shows distinct acidic and alkaline zones, which are not primarily determined by the activity of AHA H+-ATPases. Instead, the distinct domain of alkaline pH in the root transition zone is controlled by a rapid auxin response module, consisting of the AUX1 auxin influx carrier, the AFB1 auxin co-receptor, and the CNCG14 calcium channel. We demonstrate that the rapid auxin response pathway is required for an efficient navigation of the root tip.

• Klíčová slova
• A. thaliana, auxin, pH, plant biology, root,
• MeSH
• adenosintrifosfatasy metabolismus   MeSH
• Arabidopsis * metabolismus   MeSH
• kationtové kanály řízené cyklickými nukleotidy metabolismus   MeSH
• koncentrace vodíkových iontů MeSH
• kořeny rostlin MeSH
• kyseliny indoloctové metabolismus   MeSH
• proteiny huseníčku * metabolismus   MeSH
• půda MeSH
• regulace genové exprese u rostlin MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• adenosintrifosfatasy MeSH
• AUX1 protein, Arabidopsis MeSH Prohlížeč
• CNGC14 protein, Arabidopsis MeSH Prohlížeč
• kationtové kanály řízené cyklickými nukleotidy MeSH
• kyseliny indoloctové MeSH
• proteiny huseníčku * MeSH
• půda MeSH

The phytohormone auxin triggers root growth inhibition within seconds via a non-transcriptional pathway. Among members of the TIR1/AFB auxin receptor family, AFB1 has a primary role in this rapid response. However, the unique features that confer this specific function have not been identified. Here we show that the N-terminal region of AFB1, including the F-box domain and residues that contribute to auxin binding, is essential and sufficient for its specific role in the rapid response. Substitution of the N-terminal region of AFB1 with that of TIR1 disrupts its distinct cytoplasm-enriched localization and activity in rapid root growth inhibition by auxin. Importantly, the N-terminal region of AFB1 is indispensable for auxin-triggered calcium influx, which is a prerequisite for rapid root growth inhibition. Furthermore, AFB1 negatively regulates lateral root formation and transcription of auxin-induced genes, suggesting that it plays an inhibitory role in canonical auxin signaling. These results suggest that AFB1 may buffer the transcriptional auxin response, whereas it regulates rapid changes in cell growth that contribute to root gravitropism.

• Klíčová slova
• Arabidopsis, auxin signaling, calcium, gravitropism, lateral root,
• MeSH
• Arabidopsis * metabolismus   MeSH
• cytosol metabolismus   MeSH
• F-box proteiny * metabolismus   MeSH
• kořeny rostlin metabolismus   MeSH
• kyseliny indoloctové farmakologie   metabolismus   MeSH
• proteiny huseníčku * metabolismus   MeSH
• receptory buněčného povrchu genetika   metabolismus   MeSH
• regulace genové exprese u rostlin MeSH
• regulátory růstu rostlin metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• F-box proteiny * MeSH
• kyseliny indoloctové MeSH
• proteiny huseníčku * MeSH
• receptory buněčného povrchu MeSH
• regulátory růstu rostlin MeSH