The genomes of charophyte green algae, close relatives of land plants, typically do not show signs of developmental regulation by phytohormones. However, scattered reports of endogenous phytohormone production in these organisms exist. We performed a comprehensive analysis of multiple phytohormones in Viridiplantae, focusing mainly on charophytes. We show that auxin, salicylic acid, ethylene and tRNA-derived cytokinins including cis-zeatin are found ubiquitously in Viridiplantae. By contrast, land plants but not green algae contain the trans-zeatin type cytokinins as well as auxin and cytokinin conjugates. Charophytes occasionally produce jasmonates and abscisic acid, whereas the latter is detected consistently in land plants. Several phytohormones are excreted into the culture medium, including auxin by charophytes and cytokinins and salicylic acid by Viridiplantae in general. We note that the conservation of phytohormone biosynthesis and signaling pathways known from angiosperms does not match the capacity for phytohormone biosynthesis in Viridiplantae. Our phylogenetically guided analysis of established algal cultures provides an important insight into phytohormone biosynthesis and metabolism across Streptophyta.

The present study was conducted to establish a protocol for the regeneration of virus-free garlic plants through somatic embryogenesis of two Croatian garlic ecotypes. Basal parts of cloves from mother plants were cultured on a full Murashige and Skoog (MS) or modified MS medium (¼ of KNO₃ and NH₄NO₃ and 2xMgSO₄) containing 0.1 mg L⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D) or 1 mg L⁻¹ 2,4-D + 0.5 mg L⁻¹ kinetin (Kin) and representing four different treatments. Plants were regenerated in MS medium containing 0.1 mg L⁻¹ 2,4-D and rooted in a medium containing 0.05 mg L⁻¹ 1-naphthaleneacetic acid (NAA) + 0.005 mg L⁻¹ 6-(γ,γ-dimethylallylamino)purine (2iP). The presence of viruses (i.e., sanitary status) of the mother plants and regenerants was checked by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR). The mother plants were infected with onion yellow dwarf virus (OYDV) and leek yellow stripe virus (LYSV). In addition, the presence of garlic common latent virus (GCLV) was confirmed in four mother plants. Embryogenic callus developed in all four treatments with success ranging from 55% to 81% depending on treatment and ecotype. Plant conversion was significantly higher in somatic embryos developed in media containing 0.1 mg L⁻¹ 2,4-D than those developed in media containing 1 mg L⁻¹ 2,4-D + 0.5 mg L⁻¹ Kin. Virus elimination success ranged from 13.3% up to 62.5% depending on garlic ecotype and treatment. The overall rate of virus elimination by somatic embryogenesis for both treatments and ecotypes were 20.7%, 22.9%, and 30.5% for OYDV, GCLV, and LYSV, respectively. Based on these results, somatic embryogenesis has been shown to be equally or more successful in eliminating garlic viruses compared to other in vitro methods.

Summary: 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.

The resolution of the 3D structure of PIN proteins and the ability to universally predict protein structures using AlphaFold allowed us to reconsider the classification of Auxin efflux carriers within the BART superfamily, and we propose to merge members of this superfamily, possessing a characteristic fold with a helical crossover, with other families carrying this fold (BASS, NhaA, CPA and others) into a newly proposed superfamily named X-Helices Carriers (XHC). We further demonstrate a profound divergence between PIN and PILS proteins and monophyly of eukaryotic PINs with the animal cholesterol receptor GPR155/LYCHOS. We hypothesise that its signalling capacity is derived from a general feature of PIN proteins to interact with membrane lipids within the core membrane fold. Finally, we discuss the auxin-transport ability of PIN and PILS proteins in the context of the described properties of bacterial homologs that act as organic acid permeases. Disclaimer This version is a draft and it will be updated during the next few weeks. Highlights PINs are in plants and fragmentary in many algae and protists, but never in fungi Eukaryotic PINs are monophyletic together with animal cholesterol receptor GPR155 PILS are frequently present in protists and in all fungi, but not in animals PINs/PILS split is occurred very early in Prokaryota AECs belongs to proposed superfamily of transporter with helical crossover

Multiple phytohormones act as conserved developmental regulators in land plants. Although the closely related streptophyte green algae typically lack full complements of molecular pathways underlying these responses, scattered reports of endogenous phytohormone production in these organisms exist. In this study, we performed a detailed LC/MS-based analysis of several phytohormones, their precursors and metabolites in all lineages of streptophyte algae. We also included chlorophyte algae and early-diverging land plants as outgroups. Free auxin, tRNA-derived cytokinins and certain phenolics including salicylic acid were found ubiquitously. However, land plants differed from green algae by the consistent detection of abscisic acid and the presence of auxin and cytokinin conjugates and trans -zeatin, supporting the hypotheses that these three phytohormones likely came to regulate development in the ancestral land plant. By contrast, we observed a patchy distribution of jasmonates among streptophytes. We additionaly analyzed the corresponding culture and empty media to account for phytohormone excretion and environmental contamination. Extracellular auxins and cytokinins were frequently detected, while agar constituted a major external source of phenolic compounds. We provide a highly comprehensive evolution-directed screen of phytohormone compound occurrence and thoroughly discuss our data in the context of current plant hormonomics and phylogenomics. GRAPHICAL