Protein ubiquitination in auxin signaling and transport

Santos Maraschin, F. dos (2009)

Doctoral Thesis

What makes plant shoots grow towards the light, and plant roots grow down into the soil? This was a question that Charles Darwin asked himself, and his experiments more than a century ago to find the answer laid the basis for the identification of the growth hormone auxin. Auxin, or indole-3-acetic acid (IAA), directs plant growth and development through its polar cell-to-cell transport-driven asymmetric distribution. Cellular IAA concentrations determine cell division, -elongation and -differentiation by facilitating the degradation of the Aux/IAA repressor proteins and thus inducing gene expression. The presumed pathway for the programmed degradation of proteins involves the attachment of a protein called ubiquitin, leading to recognition and destruction by a molecular complex called the proteasome. Here we investigated the role of protein ubiquitination and degradation in auxin action. First, we provided evidence for the longstanding paradigm that Aux/IAA proteins are ubiquitinated prior to their proteasomal degradation. At the same time we showed that ubiquitin labeling is not necessarily required for proteasomal degradation of plant proteins. Moreover, we showed that a regulator of auxin transport polarity is also involved in fine tuning auxin responses through the ubiquitin pathway. Our results place protein ubiquitination at a central position in auxin biology and thus in the movement of plants.

• Aux/IAA
• F-box protein
• PINOID
• Proteasome
• Protein degradation
• Protoplast
• Signalosome
• Ubiquitin

• All authors: Santos Maraschin, F. dos
• Supervisor: Memelink, J.
• Co-supervisor: Offringa, R.
• Qualification: Doctor (dr.)
• Awarding Institution: Faculty of Science, Leiden University
• Date: 2009-06-25