Towards an understanding of ABP1

At the time of writing it is 10 years since the first putative auxin receptor was purified, the auxin-binding protein of maize seedlings (ABP1). Over these 10 years an enormous amount of work has been done to try and confirm that this protein is a receptor, Much of the effort has been in gathering descriptive information about the protein (its chemistry and its active sites), the genes encoding it (gene structure, promoter analysis) and the sites at which it is expressed. This information, and the probes generated during these investigations, have been put to use in functional assays to try to find out more directly what role ABP1 plays in auxin responsiveness. The key to defining a receptor is the suitability of the assay used to report on receptor occupancy and the choice of assays available for auxins is discussed in this review. It is shown how the various approaches have developed to complement each other and what they have told us about ABP1, but there are still some enigmas in the ABP1 story. Some problems appear to have been resolved, but more questions remain than have been answered and some of the ways in which these problems are being tackled are discussed.