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From 2011.igem.org

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Module 2: Auxin Xpress

Auxin, or Indole 3-acetic acid (IAA), is a plant growth hormone which is produced by several soil bacteria. We have taken the genes encoding the IAA-producing pathway from Pseudomonas savastanoi and expressed them in Escherichia coli. Following chemotaxis towards the roots and uptake by the Phyto Route module, IAA expression will promote root growth with the aim of improving soil stability.

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Overview

Auxin, also known as indole-3 acetic acid (IAA), is a well-studied plant hormone that is responsible for plant growth in response to biotic and abiotic stresses. Usually, synthetic auxins like α-Naphthaleneacetic acid (αNAA) and 2,4-Dichlorophenoxyacetic acid (2,4-D) are used as herbicides. They have been in use as herbicides for the past fifty years due to their high effectiveness and cheap cost.

Although auxin is a growth promoting hormone, it can be a metabolic burden to plants at high concentrations and therefore toxic. Synthetic auxins are extremely stable and can persist in the soil for weeks, which is why they are extremely effective herbicides. IAA, on the other hand, is chemically labile and can be easily metabolised by the plants. Therefore, if we produce IAA in our chassis, it should promote rather than stunt plant root growth.

There is still a risk that IAA can be toxic to plants at high concentrations and therefore gene expression levels were modelled in silico to inform the design of the Auxin Xpress module prior to its synthesis. We aim to produce IAA in E. coli in a controlled manner so that it never reaches the toxic threshold.

In our overall project, this module will be responsible for influencing root growth with the aim of forming intricate root networks that can effectively hold down the soil, preventing its erosion.

M1: Future Work M2: Specifications