Bio 7360P - Regulation of Plant Growth & Development (Syllabus)

Research Interests:

Auxin signaling in plants:

Plant growth and development is controlled by several pant hormones.  Of these, auxin plays a major role as it regulates growth and development throughout the life cycle of plants.  Indole acetic acid (IAA) is the major form of auxin in plants.  In addition to IAA, there are number of natural and synthetic chemicals that have auxin activity.   Some of these chemicals are being used as plant growth regulators and herbicides in agro-industry. One of the well-characterized activities related to auxin is the rapid modulation of gene expression.   This is achieved through the degradation of group of repressor proteins, called Aux/IAA proteins.   These proteins are degraded through a highly regulated mechanism known as ubiquitin-proteasome pathway.

Auxin promotes the degradation of Aux/IAA proteins by enhancing the interaction between Aux/IAA proteins and SCF^TIR1 protein complex.   The exact molecular mechanism involved in this activity is not understood completely, however recent evidence indicates that TIR1 functions as an auxin receptor in plants.   In Arabidopsis, TIR1 belongs to a gene family.  TIR1 related genes in Arabidopsis are known as AFBs. Genetic studies indicate that loss of TIR1 and AFB functions causes severe growth and developmental defects. 

The mechanisms by which auxins control plant growth and development are not completely understood.  This is especially true for the downstream targets of auxin signaling. In our lab we use combination of molecular, genetic and biochemical approaches to understand the auxin signaling mechanisms in plants.  We use the model plant Arabidopsis thaliana as our experimental organism.

Recent Publications:

Dharmasiri S, Swarup R, Mockaitis K, Dharmasiri N , Singh SK, Kowalchyk M, Marchant A, Sandberg G, Bennett M, Estelle M. (2006) AXR4 is required for asymmetric localization of the auxin influx facilitator AUX1. Science (in press).

Navarro L., Dunoyer P., Jay F., Arnold B., Dharmasiri N., Estelle M., Voinnet O., Jones J.D.G (2006) A plant miRNA contributes to antibacterial resistance by repressing Auxin signaling. Science. 312: 436-439.  PDF

Dharmasiri N, Dharmasiri S and Estelle M (2005) The F-box protein TIR1 is an auxin receptor. Nature. 435: 441- 445.  PDF

Dharmasiri N, Dharmasiri S, Weijers D, Lechner E, Yamada M, Hobbie L, Eismann JS, Jurgens G and Estelle M (2005) Plant development is regulated by a family of auxin receptor F box proteins.  Dev. Cell. 9: 109-119. PDF

Dharmasiri N. and Estelle, M. (2004) Auxin signaling and regulated protein degradation.  Trends Plant Sci. 9:302-308. PDF

Xiaoqing Yang X., Lee S., Soo J-H, Dharmasiri S., Dharmasiri N., Lei G., Jensen C., Hangarter R., Hobbie L. and Estelle M. (2004) The IAA1 protein is encoded by AXR5 and is a substrate of SCF^TIR1. Plant J. 40:772-782. PDF

Dharmasiri N, Dharmasiri S, Jones AM, Estelle M. (2003) Auxin action in a cell-free system. Curr Biol. 13(16): 1418-22. PDF

Hellmann H, Hobbie L, Chapman A, Dharmasiri S, Dharmasiri N, del Pozo C, Reinhardt D, Estelle M. (2003) Arabidopsis AXR6 encodes CUL1 implicating SCF E3 ligases in auxin regulation of embryogenesis. EMBO J. 22(13): 3314-25. PDF

Dharmasiri S, Dharmasiri N, Hellmann H, Estelle M. (2003) The RUB/Nedd8 conjugation pathway is required for early development in Arabidopsis. EMBO J. 22(8):1762-70.   PDF

Liu S, Bugos RC, Dharmasiri N, Su WW. (2001) Green fluorescent protein as a secretory reporter and a tool for process optimization in transgenic plant cell cultures. J Biotechnol. 87(1): 1-16.   PDF

Other publications/Abstracts [pdf]