TY - JOUR AB - Amid the delays due to the global pandemic, in early October 2022, the auxin community gathered in the idyllic peninsula of Cavtat, Croatia. More than 170 scientists from across the world converged to discuss the latest advancements in fundamental and applied research in the field. The topics, from signalling and transport to plant architecture and response to the environment, show how auxin research must bridge from the molecular realm to macroscopic developmental responses. This is mirrored in this collection of reviews, contributed by participants of the Auxin 2022 meeting. AU - Del Bianco, Marta AU - Friml, Jiří AU - Strader, Lucia AU - Kepinski, Stefan ID - 14709 IS - 22 JF - Journal of Experimental Botany SN - 0022-0957 TI - Auxin research: Creating tools for a greener future VL - 74 ER - TY - JOUR AB - Soluble chaperones residing in the endoplasmic reticulum (ER) play vitally important roles in folding and quality control of newly synthesized proteins that transiently pass through the ER en route to their final destinations. These soluble residents of the ER are themselves endowed with an ER retrieval signal that enables the cell to bring the escaped residents back from the Golgi. Here, by using purified proteins, we showed that Nicotiana tabacum phytaspase, a plant aspartate-specific protease, introduces two breaks at the C-terminus of the N. tabacum ER resident calreticulin-3. These cleavages resulted in removal of either a dipeptide or a hexapeptide from the C-terminus of calreticulin-3 encompassing part or all of the ER retrieval signal. Consistently, expression of the calreticulin-3 derivative mimicking the phytaspase cleavage product in Nicotiana benthamiana cells demonstrated loss of the ER accumulation of the protein. Notably, upon its escape from the ER, calreticulin-3 was further processed by an unknown protease(s) to generate the free N-terminal (N) domain of calreticulin-3, which was ultimately secreted into the apoplast. Our study thus identified a specific proteolytic enzyme capable of precise detachment of the ER retrieval signal from a plant ER resident protein, with implications for the further fate of the escaped resident. AU - Teplova, Anastasiia AU - Pigidanov, Artemii A. AU - Serebryakova, Marina V. AU - Golyshev, Sergei A. AU - Galiullina, Raisa A. AU - Chichkova, Nina V. AU - Vartapetian, Andrey B. ID - 14776 IS - 22 JF - International Journal of Molecular Sciences KW - Inorganic Chemistry KW - Organic Chemistry KW - Physical and Theoretical Chemistry KW - Computer Science Applications KW - Spectroscopy KW - Molecular Biology KW - General Medicine KW - Catalysis SN - 1422-0067 TI - Phytaspase Is capable of detaching the endoplasmic reticulum retrieval signal from tobacco calreticulin-3 VL - 24 ER - TY - JOUR AB - Auxin is the major plant hormone regulating growth and development (Friml, 2022). Forward genetic approaches in the model plant Arabidopsis thaliana have identified major components of auxin signalling and established the canonical mechanism mediating transcriptional and thus developmental reprogramming. In this textbook view, TRANSPORT INHIBITOR RESPONSE 1 (TIR1)/AUXIN-SIGNALING F-BOX (AFBs) are auxin receptors, which act as F-box subunits determining the substrate specificity of the Skp1-Cullin1-F box protein (SCF) type E3 ubiquitin ligase complex. Auxin acts as a “molecular glue” increasing the affinity between TIR1/AFBs and the Aux/IAA repressors. Subsequently, Aux/IAAs are ubiquitinated and degraded, thus releasing auxin transcription factors from their repression making them free to mediate transcription of auxin response genes (Yu et al., 2022). Nonetheless, accumulating evidence suggests existence of rapid, non-transcriptional responses downstream of TIR1/AFBs such as auxin-induced cytosolic calcium (Ca2+) transients, plasma membrane depolarization and apoplast alkalinisation, all converging on the process of root growth inhibition and root gravitropism (Li et al., 2022). Particularly, these rapid responses are mostly contributed by predominantly cytosolic AFB1, while the long-term growth responses are mediated by mainly nuclear TIR1 and AFB2-AFB5 (Li et al., 2021; Prigge et al., 2020; Serre et al., 2021). How AFB1 conducts auxin-triggered rapid responses and how it is different from TIR1 and AFB2-AFB5 remains elusive. Here, we compare the roles of TIR1 and AFB1 in transcriptional and rapid responses by modulating their subcellular localization in Arabidopsis and by testing their ability to mediate transcriptional responses when part of the minimal auxin circuit reconstituted in yeast. AU - Chen, Huihuang AU - Li, Lanxin AU - Zou, Minxia AU - Qi, Linlin AU - Friml, Jiří ID - 13212 IS - 7 JF - Molecular Plant SN - 1752-9867 TI - Distinct functions of TIR1 and AFB1 receptors in auxin signalling. VL - 16 ER - TY - JOUR AB - The 3′,5′-cyclic adenosine monophosphate (cAMP) is a versatile second messenger in many mammalian signaling pathways. However, its role in plants remains not well-recognized. Recent discovery of adenylate cyclase (AC) activity for transport inhibitor response 1/auxin-signaling F-box proteins (TIR1/AFB) auxin receptors and the demonstration of its importance for canonical auxin signaling put plant cAMP research back into spotlight. This insight briefly summarizes the well-established cAMP signaling pathways in mammalian cells and describes the turbulent and controversial history of plant cAMP research highlighting the major progress and the unresolved points. We also briefly review the current paradigm of auxin signaling to provide a background for the discussion on the AC activity of TIR1/AFB auxin receptors and its potential role in transcriptional auxin signaling as well as impact of these discoveries on plant cAMP research in general. AU - Qi, Linlin AU - Friml, Jiří ID - 13266 IS - 2 JF - New Phytologist SN - 0028-646X TI - Tale of cAMP as a second messenger in auxin signaling and beyond VL - 240 ER - TY - JOUR AB - The phytohormone auxin plays central roles in many growth and developmental processes in plants. Development of chemical tools targeting the auxin pathway is useful for both plant biology and agriculture. Here we reveal that naproxen, a synthetic compound with anti-inflammatory activity in humans, acts as an auxin transport inhibitor targeting PIN-FORMED (PIN) transporters in plants. Physiological experiments indicate that exogenous naproxen treatment affects pleiotropic auxin-regulated developmental processes. Additional cellular and biochemical evidence indicates that naproxen suppresses auxin transport, specifically PIN-mediated auxin efflux. Moreover, biochemical and structural analyses confirm that naproxen binds directly to PIN1 protein via the same binding cavity as the indole-3-acetic acid substrate. Thus, by combining cellular, biochemical, and structural approaches, this study clearly establishes that naproxen is a PIN inhibitor and elucidates the underlying mechanisms. Further use of this compound may advance our understanding of the molecular mechanisms of PIN-mediated auxin transport and expand our toolkit in auxin biology and agriculture. AU - Xia, Jing AU - Kong, Mengjuan AU - Yang, Zhisen AU - Sun, Lianghanxiao AU - Peng, Yakun AU - Mao, Yanbo AU - Wei, Hong AU - Ying, Wei AU - Gao, Yongxiao AU - Friml, Jiří AU - Weng, Jianping AU - Liu, Xin AU - Sun, Linfeng AU - Tan, Shutang ID - 13209 IS - 6 JF - Plant Communications TI - Chemical inhibition of Arabidopsis PIN-FORMED auxin transporters by the anti-inflammatory drug naproxen VL - 4 ER - TY - JOUR AB - As a crucial nitrogen source, nitrate (NO3−) is a key nutrient for plants. Accordingly, root systems adapt to maximize NO3− availability, a developmental regulation also involving the phytohormone auxin. Nonetheless, the molecular mechanisms underlying this regulation remain poorly understood. Here, we identify low-nitrate-resistant mutant (lonr) in Arabidopsis (Arabidopsis thaliana), whose root growth fails to adapt to low-NO3− conditions. lonr2 is defective in the high-affinity NO3− transporter NRT2.1. lonr2 (nrt2.1) mutants exhibit defects in polar auxin transport, and their low-NO3−-induced root phenotype depends on the PIN7 auxin exporter activity. NRT2.1 directly associates with PIN7 and antagonizes PIN7-mediated auxin efflux depending on NO3− levels. These results reveal a mechanism by which NRT2.1 in response to NO3− limitation directly regulates auxin transport activity and, thus, root growth. This adaptive mechanism contributes to the root developmental plasticity to help plants cope with changes in NO3− availability. AU - Wang, Yalu AU - Yuan, Zhi AU - Wang, Jinyi AU - Xiao, Huixin AU - Wan, Lu AU - Li, Lanxin AU - Guo, Yan AU - Gong, Zhizhong AU - Friml, Jiří AU - Zhang, Jing ID - 13201 IS - 25 JF - Proceedings of the National Academy of Sciences of the United States of America SN - 0027-8424 TI - The nitrate transporter NRT2.1 directly antagonizes PIN7-mediated auxin transport for root growth adaptation VL - 120 ER - TY - THES AU - Gnyliukh, Nataliia ID - 14510 KW - Clathrin-Mediated Endocytosis KW - vesicle scission KW - Dynamin-Related Protein 2 KW - SH3P2 KW - TPLATE complex KW - Total internal reflection fluorescence microscopy KW - Arabidopsis thaliana SN - 2663-337X TI - Mechanism of clathrin-coated vesicle formation during endocytosis in plants ER - TY - JOUR AB - Auxin has always been at the forefront of research in plant physiology and development. Since the earliest contemplations by Julius von Sachs and Charles Darwin, more than a century-long struggle has been waged to understand its function. This largely reflects the failures, successes, and inevitable progress in the entire field of plant signaling and development. Here I present 14 stations on our long and sometimes mystical journey to understand auxin. These highlights were selected to give a flavor of the field and to show the scope and limits of our current knowledge. A special focus is put on features that make auxin unique among phytohormones, such as its dynamic, directional transport network, which integrates external and internal signals, including self-organizing feedback. Accented are persistent mysteries and controversies. The unexpected discoveries related to rapid auxin responses and growth regulation recently disturbed our contentment regarding understanding of the auxin signaling mechanism. These new revelations, along with advances in technology, usher us into a new, exciting era in auxin research. AU - Friml, Jiří ID - 10016 IS - 5 JF - Cold Spring Harbor Perspectives in Biology SN - 1943-0264 TI - Fourteen stations of auxin VL - 14 ER - TY - JOUR AB - The synthetic strigolactone (SL) analog, rac-GR24, has been instrumental in studying the role of SLs as well as karrikins because it activates the receptors DWARF14 (D14) and KARRIKIN INSENSITIVE 2 (KAI2) of their signaling pathways, respectively. Treatment with rac-GR24 modifies the root architecture at different levels, such as decreasing the lateral root density (LRD), while promoting root hair elongation or flavonol accumulation. Previously, we have shown that the flavonol biosynthesis is transcriptionally activated in the root by rac-GR24 treatment, but, thus far, the molecular players involved in that response have remained unknown. To get an in-depth insight into the changes that occur after the compound is perceived by the roots, we compared the root transcriptomes of the wild type and the more axillary growth2 (max2) mutant, affected in both SL and karrikin signaling pathways, with and without rac-GR24 treatment. Quantitative reverse transcription (qRT)-PCR, reporter line analysis and mutant phenotyping indicated that the flavonol response and the root hair elongation are controlled by the ELONGATED HYPOCOTYL 5 (HY5) and MYB12 transcription factors, but HY5, in contrast to MYB12, affects the LRD as well. Furthermore, we identified the transcription factors TARGET OF MONOPTEROS 5 (TMO5) and TMO5 LIKE1 as negative and the Mediator complex as positive regulators of the rac-GR24 effect on LRD. Altogether, hereby, we get closer toward understanding the molecular mechanisms that underlay the rac-GR24 responses in the root. AU - Struk, Sylwia AU - Braem, Lukas AU - Matthys, Cedrick AU - Walton, Alan AU - Vangheluwe, Nick AU - Van Praet, Stan AU - Jiang, Lingxiang AU - Baster, Pawel AU - De Cuyper, Carolien AU - Boyer, Francois-Didier AU - Stes, Elisabeth AU - Beeckman, Tom AU - Friml, Jiří AU - Gevaert, Kris AU - Goormachtig, Sofie ID - 10583 IS - 1 JF - Plant & Cell Physiology KW - flavonols KW - MAX2 KW - rac-Gr24 KW - RNA-seq KW - root development KW - transcriptional regulation SN - 0032-0781 TI - Transcriptional analysis in the Arabidopsis roots reveals new regulators that link rac-GR24 treatment with changes in flavonol accumulation, root hair elongation and lateral root density VL - 63 ER - TY - JOUR AB - Much of what we know about the role of auxin in plant development derives from exogenous manipulations of auxin distribution and signaling, using inhibitors, auxins and auxin analogs. In this context, synthetic auxin analogs, such as 1-Naphtalene Acetic Acid (1-NAA), are often favored over the endogenous auxin indole-3-acetic acid (IAA), in part due to their higher stability. While such auxin analogs have proven to be instrumental to reveal the various faces of auxin, they display in some cases distinct bioactivities compared to IAA. Here, we focused on the effect of auxin analogs on the accumulation of PIN proteins in Brefeldin A-sensitive endosomal aggregations (BFA bodies), and the correlation with the ability to elicit Ca 2+ responses. For a set of commonly used auxin analogs, we evaluated if auxin-analog induced Ca 2+ signaling inhibits PIN accumulation. Not all auxin analogs elicited a Ca 2+ response, and their differential ability to elicit Ca 2+ responses correlated partially with their ability to inhibit BFA-body formation. However, in tir1/afb and cngc14, 1-NAA-induced Ca 2+ signaling was strongly impaired, yet 1-NAA still could inhibit PIN accumulation in BFA bodies. This demonstrates that TIR1/AFB-CNGC14-dependent Ca 2+ signaling does not inhibit BFA body formation in Arabidopsis roots. AU - Wang, R AU - Himschoot, E AU - Grenzi, M AU - Chen, J AU - Safi, A AU - Krebs, M AU - Schumacher, K AU - Nowack, MK AU - Moeder, W AU - Yoshioka, K AU - Van Damme, D AU - De Smet, I AU - Geelen, D AU - Beeckman, T AU - Friml, Jiří AU - Costa, A AU - Vanneste, S ID - 10717 IS - 8 JF - Journal of Experimental Botany SN - 0022-0957 TI - Auxin analog-induced Ca2+ signaling is independent of inhibition of endosomal aggregation in Arabidopsis roots VL - 73 ER -