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The triple response phenotype is characteristic for seedlings treated with the phytohormone ethylene or its direct precursor 1-aminocyclopropane-carboxylic acid, and is often employed to find novel chemical tools to probe ethylene responses. We identified a benzoxazole-urea derivative (B2) partially mimicking ethylene effects in a triple response bioassay. A phenotypic analysis demonstrated that B2 and its closest analogue arinole (ARI) induced phenotypic responses reminiscent of seedlings with elevated levels of auxin, including impaired hook development and inhibition of seedling growth. Specifically, ARI reduced longitudinal cell elongation in roots, while promoting cell division. In contrast to other natural or synthetic auxins, ARI mostly acts as an inducer of adventitious root development, with only limited effects on lateral root development. Quantification of free auxins and auxin biosynthetic precursors as well as auxin-related gene expression demonstrated that ARI boosts global auxin levels. In addition, analyses of auxin reporter lines and mutants, together with pharmacological assays with auxin-related inhibitors, confirmed that ARI effects are facilitated by TRYPTOPHAN AMINOTRANSFERASE1 (TAA1)-mediated auxin synthesis. ARI treatment in an array of species, including Arabidopsis, pea, tomato, poplar, and lavender, resulted in adventitious root formation, which is a desirable trait in both agriculture and horticulture. [ABSTRACT FROM AUTHOR]

Alternaria species are notorious pathogens of solanaceous crops and are known to produce a plethora of toxins. Nevertheless, the involvement of toxins or other virulence factors in Alternaria infections on potato plants has never been investigated. In view of this, we analysed whether different Alternaria species produced host‐ and non‐host‐specific toxins in vitro and in vivo. Secondly, we assessed if ethylene (ETH) is involved in potato plant infections, as was previously demonstrated in tomato. Although many toxins were detected in vitro, no toxins were present before symptom appearance in potato leaves. Isolates that made large conidia (A. solani) produced up to six times more ETH in vitro than isolates with small conidia (A. arborescens) in the presence of the ETH precursor α‐keto‐γ‐methylthiobutyric acid (KMBA). In contrast, on potato leaf discs, an inverse relation was found between ETH emission and conidia size after correcting the data according to fungal DNA content, suggesting a role for ETH in symptom development rather than initiation. Moreover, application of a plant ETH biosynthesis inhibitor, 2‐aminoethoxyvinyl glycine (AVG), resulted in a 60% reduction in necrosis after inoculation with a large‐conidia isolate, whereas a 35% increase in necrosis was observed after inoculation with a small‐conidia isolate. Finally, it was concluded that toxin production is not essential for symptom development of Alternaria on potato and that ETH (either from the plant and/or the fungus) is a crucial factor in symptom development by A. solani, whereas its role was found to be antagonistic for A. arborescens. [ABSTRACT FROM AUTHOR]

The simplest unsaturated hydrocarbon, ethylene or ethene, is one of the most widely produced organic chemicals worldwide. It serves as a building block for various materials and chemicals, including plastics, ethanol, detergents, and many more. Strikingly, it also acts as a signaling molecule in virtually all physiological processes and during all developmental stages in plant life. Plant biologists consider ethylene to have a tripartite role in plant development; this gaseous molecule can serve as a plant growth regulator, an aging hormone, and as a stress controller, aiding in defense against both biotic and abiotic stressors. Therefore, the regulation of the ethylene status is indispensable in both agricultural and horticultural practices. Since its discovery as a phytohormone, many chemicals have been developed that are able to affect ethylene responses in plants. Here, an extensive overview of the current toolbox of ethylene regulators, their discovery, function, and applications in both the agri‐ and horticultural field is presented. Furthermore, possibilities and considerations related to novel small molecules, such as those emerging from the chemical genetics field, are discussed. [ABSTRACT FROM AUTHOR]

The volatile two-carbon hormone ethylene acts in concert with an array of signals to affect etiolated seedling development. From a chemical screen, we isolated a quinoline carboxamide designated ACCERBATIN (AEX) that exacerbates the 1-aminocyclopropane-1-carboxylic acid-induced triple response, typical for ethylene-treated seedlings in darkness. Phenotypic analyses revealed distinct AEX effects including inhibition of root hair development and shortening of the root meristem. Mutant analysis and reporter studies further suggested that AEX most probably acts in parallel to ethylene signaling. We demonstrated that AEX functions at the intersection of auxin metabolism and reactive oxygen species (ROS) homeostasis. AEX inhibited auxin efflux in BY-2 cells and promoted indole-3-acetic acid (IAA) oxidation in the shoot apical meristem and cotyledons of etiolated seedlings. Gene expression studies and superoxide/hydrogen peroxide staining further revealed that the disrupted auxin homeostasis was accompanied by oxidative stress. Interestingly, in light conditions, AEX exhibited properties reminiscent of the quinoline carboxylate-type auxin-like herbicides. We propose that AEX interferes with auxin transport from its major biosynthesis sites, either as a direct consequence of poor basipetal transport from the shoot meristematic region, or indirectly, through excessive IAA oxidation and ROS accumulation. Further investigation of AEX can provide new insights into the mechanisms connecting auxin and ROS homeostasis in plant development and provide useful tools to study auxin-type herbicides. [ABSTRACT FROM AUTHOR]