Ethylene and Auxin Crosstalk

Auxin and Ethylene cross talk in regulation of root gravitropism and development 

We are interested in the mechanisms by which auxin transport is regulated to allow gravitropic responses and lateral root development.  Recent experiments have focused on asking whether the gaseous plant hormone, ethylene, regulates auxin transport and dependent physiological processes.  We have found that ethylene negatively regulates root (Buer et al. 2006) and shoot gravitropism (Muday et al. 2006).  When mutants that have defects proteins that mediate auxin signaling, such as EIN2 or ETR1, are treated with ethylene, the inhibition of gravitropic curvature are lost, suggesting that ethylene negatively regulates gravitropism through well established ethylene signaling pathways. We also found that roots of the tt4 mutant, which makes no flavonoids, is insensitive to inhibition by ethylene treatment, suggesting that this mutant may have ethylene dependent flavonoid synthesis that regulates gravitropism (Buer et al., 2006).  Consistent with this possibility, there are localized changes in flavonoids in response to gravitropic reorientation (Buer and Muday, 2004) and ethylene treatment (Buer et al. 2006). The image shows the enhanced accumulation of flavonoids in Arabidopsis roots treated with the ethylene precursor, ACC for 1, 2, and 4 hours.  Current experiments are focused on exploring the molecular mechanisms by which ethylene and auxin control flavonoid synthesis.   

Lateral root initiation and elongation are under the control of auxin (Reed et al. 1998).  We are interested in asking whether there is also crosstalk between auxin and ethylene in controlling this process.  We are currently examining the effect of ethylene treatment or lateral and adventitious root formation in both Arabidopsis and tomato and in mutants of these two species that are defective in ethylene signaling. If we find interaction between these two hormones in regulating root development, we will focus our experiments on identification of the molecular mechanisms by which this crosstalk regulates root development.

(undergraduate students underlined, graduate students in bold)

Lewis, DR, Negi, S, Sukumar, P, Muday, GK (In review) Ethylene inhibits lateral root development and enhances IAA transport by altered expression and localization of auxin transport proteins. Development

Lewis, DR, Ramirez, MV, Miller, ND, Keith, R, Helm, R, Winkel, BSJ, Muday, GK (In review) Auxin and ethylene induce distinct flavonol accumulation patterns through independent transcriptional networks: Plant Physiol

Negi, S, Sukumar, P, Liu, X, Cohen, JD, and Muday, GK (2010) Genetic dissection of the role of ethylene in regulating auxin dependent lateral and adventitious root formation in tomato. Plant Journal 61: 3-15

Lewis, DR and Muday, GK (2009) Measurement of auxin transport in Arabidopsis thaliana. Nature Protocols: 4: 437-451.

Negi, S, Ivanchenko, MG, and Muday, GK (2008) Ethylene regulates lateral root formation and auxin transport in Arabidopsis thaliana. Plant J. 55: 175-187

Ivanchenko, MG, Muday, GK, and Dubrovsky, JG. (2008) Ethylene-auxin interactions regulate lateral root initiation and emergence in Arabidopsis thaliana. Plant J. 55: 335-347

Buer, CS, Sukumar, P, and Muday, GK (2006) Ethylene induced flavonoid synthesis modulates root gravitropism. Plant Physiology: 140: 1384-1396

Buer, CS, and Muday, GK (2004) The transparent testa4 mutation prevents flavonoid synthesis and alters auxin transport and the response of Arabidopsis roots to gravity and light. Plant Cell, 16: 1191-1205.

Buer, CS, Sukumar, P, and Muday, GK (2006) Ethylene induced flavonoid synthesis modulates root gravitropism. Plant Physiology: 140: 1384-1396

Muday, GK, Brady1, SR, Argueso, C., Deruère, J, Kieber, JJ, and DeLong, A. (2006) RCN1-regulated phosphatase activity and EIN2 modulate hypocotyl gravitropism by a mechanism that does not require ethylene signaling. Plant Physiology: 141: 1617-1629

Muday, GK and Rahman, A (2006) Auxin transport and the integration of gravitropic growth.  In Plant Tropisms: eds Gilroy, S and Masson, P, Blackwell Publishing; In press

Reed RC, Brady, SR, Muday GK (1998) Inhibition of Auxin Movement From the Shoot into the Root Inhibits Lateral Root Development in Arabidopsis thaliana. Plant Physiol. 118: 1369-1378.