The Muday Laboratory, Wake Forest University

Auxin Transport and Root Development

lateral roots comparedThe formation and elongation of lateral roots requires auxin transport, as mutations or chemical inhibitors which reduce auxin transport reduce lateral root formation in a variety of plants including Arabidopsis and tomato (Muday et al. 1994; Rashotte et al. 2000).  In roots, there are two polarities of auxin movement that are linked to different physiological processes.  IAA moves acropetally, toward the root apex, through the central cylinder and basipetally, from the apex toward the base, through the outer layer of cells (Muday and DeLong, 2001).  In Arabidopsis, both of these polarities of IAA movement have been detected and linked to specific physiological processes (Reed et al., 1998, Rashotte et al., 2000). Acropetal movement of IAA from the shoot into the root has been implicated in the control of lateral root development (Reed et al., 1998), while basipetal movement of IAA from the root tip back has been linked to gravity response (Rashotte et al., 2000). Evidence in support of acropetal IAA transport in controlling root development is shown in the associated image, in which either control agar or agar containing the auxin transport inhibitor, naphthylphthalamic acid (NPA), was applied locally to the root shoot junction.  Root elongation is inhibited by NPA applied at the root base, but not at the root tip.

We are interested in understanding the mechanisms that control auxin transport into the root and thereby drive lateral root development. Mutations that block flavonoid synthesis lead to increased auxin transport and lateral root development, consistent with the absence of a negative regulator of auxin transport (Brown et al. 2001).  The rcn1 mutation, in a gene encoding a protein phosphatase regulatory subunit has altered regulation of auxin transport and root branching by the auxin transport inhibitor, naphthylphthalamic acid (Rashotte et al. 2001).  Current studies are also examining the role of ethylene in regulating both lateral and adventitious root formation in both tomato and Arabidopsis plants. Finally, we are also interested in understanding whether changes in the environment, such as amount of light or the growth temperature, control root development and whether this regulation is mediated by modulation of auxin transport.

(graduate students in bold, undergradutes underlined)

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

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

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

Brown, DE, Rashotte, AM, Murphy, AS, Normanly, J, Tague, BW, Peer , WS, Taiz ,L , and Muday, GK (2001) Flavonoids act as negative regulators of auxin transport in vivo in Arabidopsis. Plant Physiol 126: 524-53

Muday, GK and P Haworth (1994) Tomato root growth, gravitropism, and lateral development:  Correlations with auxin transport.  Plant Physiology and Biochemistry 32, 193-203.

Rashotte, AM, Brady, SR, Reed, RC, Ante, SJ, Muday, GK (2000) Basipetal Auxin Transport Is Required for Gravitropism in Roots of Arabidopsis thaliana. Plant Physiol. 122: 481-490.

Rashotte, AM, DeLong, A, and Muday, GK (2001) Genetic and chemical reductions in protein phosphatase activity alter auxin transport, gravity response and lateral root elongation. Plant Cell 13: 1683-1697

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.  

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