Team:UNSW Australia/Lab/Plants
Plants
Overview
Auxins are plant hormones which are involved in the regulation of plant growth and development. The biosynthesis of the auxin indole-3-aecetic acid (IAA) was used as a test pathway for our scaffold system, thus a protocol was developed to investigate the functionality of biosynthetically produced IAA in a plant growth assay compared to commercially available IAA. Arabidopsis thaliana seedlings were grown in media containing varying concentrations of IAA, to observe its effect on growth and development. Reduced primary root growth and high lateral root number was observed at higher concentrations of IAA, exhibiting phenotypes common with a stress induced morphology. These results, in addition to comments made by PlantBank researchers who had found that addition of exogenous IAA showed no benefit, indicated that IAA synthesis was not an appropriate pathway to purse for commercialisation with our scaffold. Despite this, the UNSW iGEM team was able to develop a protocol that could be used in the future to observe the functionality of the IAA product produced with our scaffold compared with commercially available IAA.
Introduction
Auxins are plant hormones (phytohormones) which are involved in the regulation of plant growth and development1. Indole acetic acid (IAA) is the most widely characterised auxin, and the primary auxin in most plant species2. It is associated with many physiological processes in plants including cell elongation, cell division, tropisms to light and gravity, and root initiation and development1.
Plants can naturally synthesise auxins, and the biosynthesis of IAA in A. thaliana occurs predominantly through a tryptophan dependent pathway utilising proteins from the tryptophan amino transferase of Arabidopsis (TAA) and Yucca (YUC) flavin monooxygenase-like protein families3. Bacteria can also synthesise IAA through a variety of pathways, and often utilise IAA to interact with and colonise plants4. To test our scaffold system we chose the two-step indole-3-acetamide pathway for IAA biosynthesis, the best characterised IAA biosynthetic pathway in bacteria4, as a proof of concept.
Although plants can synthesise IAA de novo, application of exogenous phytohormones is common in industry to stimulate specific responses5. Thus auxins, and phytohormones more broadly, have commercial significance. One example of this is the use of phytohormones in tissue culture. Tissue culture, which grows plant cells, tissues and organs, on nutrient medium in controlled aseptic conditions has many commercial applications including propagation of valuable samples which can not be propagated by traditional methods6.