Auxins are a class of growth hormone found in plants that induce cells to elongate. They act rapidly through the mediation of a single receptor or multiple receptors to cause changes in cell wall properties and gene expression. There are now several candidate auxin receptors in plants; however, their roles in growth and development have not yet been determined. These putative receptors are therefore designated "auxin-binding proteins" (ABP's). This project focuses on the characterization of two such ABP's, designated ABP1 and 65-kDa ABP. ABP1 is an endoplasmic reticulum (ER) protein that contains an ER-retention sequence; yet, this laboratory has demonstrated that a significant amount of this protein escapes the ER retention mechanism and uniquely migrates to the plasma membrane / cell wall space. This cell wall localization is consistent with its postulated site of action. The 65-kDa subunit ABP, recently identified in this laboratory using anti- idiotypic antibodies, is a nuclear localized protein. Preliminary data suggest that it binds DNA. The hypothesis is put forward that this putative receptors is involved in auxin-regulated gene transcription. %%% It has been known for many years that plant growth and development is regulated by plant hormones, principally auxins (e.g., indole acetic acid, or IAA) and cytokines. However, despite a great deal of effort, it is not yet understood how plant hormones exert their effects at a molecular level. Auxin-binding proteins, such as ABP1 and the 65-kDa ABP which are the subject of this project, have been described, but it has not yet been established for any of these that they are functional "auxin receptors," let alone mechanisms of action. This laboratory has made some very interesting and novel findings, such as the auxin-dependent subcellular localization of ABP1 and the nuclear localization and DNA binding characteristics of 65-kDa ABP, which may lead to breakthroughs in this area. An understanding of how plant cell growth and development is normally controlled or modulated by plant hormones is critical to this nation's agricultural biotechnology efforts.
