Insights into ROS-dependent signalling underlying transcriptomic plant responses to the herbicide 2,4-D

The synthetic auxin 2,4¿dichlorophenoxyacetic acid (2,4¿D) functions as an agro-nomic weed control herbicide. High concentrations of 2,4¿D induce plant growthdefects, particularly leaf epinasty and stem curvature. Although the 2,4¿D triggeredreactive oxygen species (ROS) production, little is known about its signalling. In thisstudy, by using a null mutant in peroxisomal acyl CoA oxidase 1 (acx1¿2), we iden-tified acyl¿coenzyme A oxidase 1 (ACX1) as one of the main sources of ROS pro-duction and, in part, also causing the epinastic phenotype following 2,4¿Dapplication. Transcriptomic analyses of wild type (WT) plants after treatment with2,4¿D revealed a ROS¿related peroxisomal footprint in early plant responses, whileother organelles, such as mitochondria and chloroplasts, are involved in later re-sponses. Interestingly, a group of 2,4¿D¿responsive ACX1¿dependent transcriptspreviously associated with epinasty is related to auxin biosynthesis, metabolism, andsignalling. We found that the auxin receptor auxin signalling F¿box 3 (AFB3), acomponent of Skp, Cullin, F¿box containing complex (SCF) (ASK¿cullin¿F¿box) E3ubiquitin ligase complexes, which mediates auxin/indole acetic acid (AUX/IAA)degradation by the 26S proteasome, acts downstream of ACX1 and is involved in theepinastic phenotype induced by 2,4¿D. We also found that protein degradationassociated with ubiquitin E3¿RING and E3¿SCF¿FBOX in ACX1¿dependent signallingin plant responses to 2,4¿D is significantly regulated over longer treatment periods

This study was funded by the Spanish Ministry of Science, Innovation and Universities (MCIU), the State Research Agency (AEI) and FEDER grant PGC2018-098372-B-I00. MAP-V was supported by MCIU Research Personnel Training (FPI) grant BES-2016-076518.