AUXIN-BINDING PROTEINS AND THEIR POSSIBLE ROLES IN AUXINMEDIATED PLANT-CELL GROWTH

Like several other classes of hormones, the class of plant hormones called auxins exert myriad effects on cell development. While auxins are most noted for inducing cell elongation, they are also involved in cell division, cell differentiation, cell and organ polarity, and wound responsiveness. Consistent with this pleiotropy, is the recent identification of several putative auxin receptors that in theory could represent the primary elements of more than one auxin signal pathway leading to distinct responses or leading in parallel to a single response. Our current working hypothesis is that some auxin-mediated responses may be mediated by multiple receptors. We describe some of what is known about each of the new putative receptors and elaborate on the hypothesis using the example of cell elongation. Specifically for auxin-induced elongation, we propose that two rapid events, specific gene transcription and cell wall acidification, are separately mediated by at least two receptors, acting in the nucleus and at the plasma membrane, respectively.