9808792 Jones Dr. Jones has recently obtained molecular genetic evidence that auxin-binding protein I (ABP1) is an auxin receptor that mediates auxin-regulated growth and cell wall formation. Constitutive expression of maize ABP1 in maize cell lines causes increases in both cell size and wall thickness. Furthermore, inducible expression of arabidopsis ABP1 in tobacco causes increased growth as measured in leaf explants. Consistent with receptor function, the ABP1 effect in both systems is strictly dependent on auxin. The molecular mechanism by which ABP1 causes increase in growth is not known and is the topic of investigation for this proposal. Based on its subcellular distribution, the PI hypothesizes that the ABP1-auxin complex triggers a change in the control of rate and/or direction of flow of wall precursors and/or growth-limiting factors through the endomembrane pathway or alters the sorting and activity of wall precursors or their biosynthetic enzymes. To test this hypothesis, the PI will investigate auxin-regulated cell and tissue growth, auxin uptake, and polar auxin transport will be assessed in arabidopsis and tobacco plants and explants that have both increased and decreased levels on ABP1. This proposal addresses a central question in plant cell biology, growth, and development: How does auxin regulate plant growth? The signal transduction pathway delineated by auxin and ABP1 is certainly only part of multiple pathways that lead to cell expansion but all the evidence so far indicate that it is novel.
