Affiliation:
1. Plant Developmental Genetics, Institute of Biology Leiden Leiden University Sylviusweg 72 2333 BE Leiden Netherlands
2. Department of Chemical Biology and Drug Discovery, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Center for Biomedical Research Utrecht University Universiteitsweg 99 3584CG Utrecht The Netherlands
3. Center for Cooperative Research in Biomaterials (CIC biomaGUNE), Basque Research and Technology Alliance (BRTA) Paseo de Miramon 182 20014 Donostia San Sebastián Spain
Abstract
SUMMARY2,4‐dichlorophenoxyacetic acid (2,4‐D) is a synthetic analogue of the plant hormone auxin that is commonly used in many in vitro plant regeneration systems, such as somatic embryogenesis (SE). Its effectiveness in inducing SE, compared to the natural auxin indole‐3‐acetic acid (IAA), has been attributed to the stress triggered by this compound rather than its auxinic activity. However, this hypothesis has never been thoroughly tested. Here we used a library of forty 2,4‐D analogues to test the structure–activity relationship with respect to the capacity to induce SE and auxinic activity in Arabidopsis thaliana. Four analogues induced SE as effectively as 2,4‐D and 13 analogues induced SE but were less effective. Based on root growth inhibition and auxin response reporter expression, the 2,4‐D analogues were classified into different groups, ranging from very active to not active auxin analogues. A halogen at the 4‐position of the aromatic ring was important for auxinic activity, whereas a halogen at the 3‐position resulted in reduced activity. Moreover, a small substitution at the carboxylate chain was tolerated, as was extending the carboxylate chain with an even number of carbons. The auxinic activity of most 2,4‐D analogues was consistent with their simulated TIR1‐Aux/IAA coreceptor binding characteristics. A strong correlation was observed between SE induction efficiency and auxinic activity, which is in line with our observation that 2,4‐D‐induced SE and stress both require TIR1/AFB auxin co‐receptor function. Our data indicate that the stress‐related effects triggered by 2,4‐D and considered important for SE induction are downstream of auxin signalling.
Funder
Nederlandse Organisatie voor Wetenschappelijk Onderzoek
H2020 Marie Skłodowska-Curie Actions
Subject
Cell Biology,Plant Science,Genetics