The Muday Laboratory, Wake Forest University

The role of auxin transport in embryo polarity
using Fucus as a model system


A number of recent reports have implicated the plant hormone auxin and its polar transport in plant embryo and vascular development, using both genetic mutants and auxin transport inhibitor treatments. Several Arabidopsis mutants have been identified that have altered embryo development and appear to have a primary defect in auxin response or homeostasis. We are interested in determining whether auxin transport is also important during the first embryonic division and are using embryos of the brown alga, Fucus distichus to test this possibility. Fucus embryos normally develop with a single unbranched rhizoid, as shown above in panel A, but growth on the auxin, IAA, or the auxin transport inhibitor NPA (as shown in panel Band C above) leads to formation of embryos with either branched and multiple rhizoids (Basus et. al., 2002). These embryo alterations are induced by as little as two hours exposure to these compounds immediately after fertilization and the effects are complete within the first 6 hours, suggesting that auxin plays a role in initial stages of development. IAA accumulation in embryos is regulated by auxin transport inhibitors that act at the site of the auxin efflux carrier, but IAA uptake appears to be carrier independent. Indole-3-acetic acid (IAA) was identified in Fucus embryos and mature tissues by gas chromatography-mass spectroscopy. These results suggest that early stages of Fucus embryo development including orientation of polarity and developmental pattern are interconnected with auxin transport (Basus et. al., 2002). Current efforts are focused on understanding how auxin influences the early stages of Fucus embryo development and the relationship between the role of auxin and the previously established role of the actin cytoskeleton in Fucus embryo development.
The orientation of the position of rhizoid formation in Fucus embryos is sensitive to environmental gradients. We have recently found that in addition to the well characterized response to light, these embryos are also weakly polarized by gravity (Sun et al., 2004). The directional control of the position of rhizoid formation in response to light and gravity are both lost when embryos are treated with auxin and auxin transport inhibitors. Additionally, actin patches, which predict the site of rhizoid formation, are randomized by auxin transport inhibitors. Together, these results are consistent with a mechanism that uses the process of auxin transport to communicate environmental signals to control the position of actin patch formation (Sun et al., 2004).

Sun, H, Basu, S, Brady, SR, Luciano, RL, and Muday, GK (2004) Interactions between auxin transport and the actin cytoskeleton in developmental polarity of Fucus distichus embryos in response to light and gravity. Plant Physiol.: 135: 266-278

Basu, S, Sun, H, Brian, L, Quatrano, RL, and Muday, GK (2002) Early embryo development in Fucus distichus is auxin dependent. Plant Physiology. 130: 292-302

see also [Pubmed List of Papers]

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