Ethylene Controls Adventitious Root Initiation Sites in Arabidopsis Hypocotyls Independently of Strigolactones

Abstract

mutants together with GR24 (strigolactone agonist) treatments. Importantly, we conducted a detailed mapping of adventitious root initiation along the hypocotyl and measured ethylene production in strigolactone mutants. ACC treatments resulted in a slight increase in adventitious root formation at low doses and a decrease at higher doses, in both wild-type and strigolactone mutants. Furthermore, the distribution of adventitious roots dramatically changed to the top third of the hypocotyl in a dose-dependent manner with ACC treatments in both wild-type and strigolactone mutants. The ethylene mutants all responded to treatments with GR24. Wild type and max4 (strigolactone-deficient mutant) produced the same amount of ethylene, while emanation from max2 (strigolactone-insensitive mutant) was lower. We conclude that strigolactones and ethylene act largely independently in regulating adventitious root formation with ethylene controlling the distribution of root initiation sites. This role for ethylene may have implications for Abstract Adventitious root formation is essential for cutting propagation of diverse species; however, until recently little was known about its regulation. Strigolactones and ethylene have both been shown to inhibit adventitious roots and it has been suggested that ethylene interacts with strigolactones in root hair elongation. We have investigated the interaction between strigolactones and ethylene in regulating adventitious root formation in intact seedlings of Arabidopsis thaliana. We used strigolactone mutants together with 1-aminocyclopropane-1-carboxylic acid (ACC) (ethylene precursor) treatments and ethylene Yuming Hu and Thomas Depaepe have contributed equally to this work.The original version of this article was revised: The name of the sixth author was misspelled. However, it has been corrected in this version. flood response because both ethylene and adventitious root development are crucial for flood tolerance. Electronic supplementary material

Control of Adventitious Root Architecture in Rice by Darkness, Light, and Gravity

“…In prolonged darkness, plants start to senesce, a process that is promoted by ethylene (Johnson and Ecker, 1998;Wang et al, 2002). Ethylene accumulation during an extended dark period has been shown previously for rice and Arabidopsis (Fukao et al, 2012;Rasmussen et al, 2017). In this study, we show that inhibition of ethylene signaling abolishes dark-induced AR emergence, supporting the conclusion that AR growth is mediated by ethylene both in the dark and during submergence.…”

Control of adventitious root formation: insights into synergistic and antagonistic hormonal interactions

“…Both ethylene overproducing 2‐1 and eto3‐1 mutants, and constitutive triple response1‐1 mutants, which have constitutive ET signaling, produced more ARs, while ethylene insensitive2‐1 and ein3‐1 mutants produced fewer ARs, than wild‐type controls. To the same end, Rasmussen et al () showed that at very low concentration (0.01 μM) ACC induced slightly higher AR densities, but higher concentrations (0.1–1 μM) had no significant effect. These results clearly indicate that ET biosynthesis and signaling promote AR formation.…”

“…SLs apparently promote AR formation in rice via the D4‐dependent pathway, probably by modulating IAA transport (Sun et al ). However, they seem to inhibit AR formation in tomato ( S. lycopersicum ), pea ( Pisum sativum ) and Arabidopsis (Kohlen et al , Rasmussen et al , ). Kohlen et al () found that AR numbers were significantly increased in CAROTENOID CLEAVAGE DIOXYGENASE 8 ( SlCCD8 ) RNAi transgenic lines, suggesting that SL‐mediated AR formation is species‐dependent.…”

Regulation of Root Development and Architecture by Strigolactones under Optimal and Nutrient Deficiency Conditions

“…In A. thaliana it acts as a negative regulator of AR formation, similar to SLs. While A. thaliana SL mutants are sensitive to treatment with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, mutants in ethylene biosynthesis and signalling are sensitive to racGR24 treatment [ 60 ]. When both hormones were applied the response was stronger in comparison to the single treatments, an indication that both phytohormones act independently in the repression of AR development [ 60 ].…”