The active, polar transport of the plant growth hormone auxin is essential to the control of plant development. Dr. Lomax has used a simple but powerful approach to isolate the IAA uptake symport by photoaffinity labelling of the protein in purified plant plasma membranes with a tritiated azido-IAA analogue. She has found that the azido-IAA specifically labels two polypeptides of 40 and 42kD in plasma membranes isolated from Cucurbita pepo hypcotyls. Both polypeptides are labeled by azido-IAA with high specific activity, behave as intrinsic membrane proteins, and exhibit a competition specificity for various auxin analogs very similar to that for in vitro and in vivo auxin transport. These data suggest that the protein doublet may be an auxin transport carrier(s). The overall goals of this project are the establishment of function for these specific plasma membrane auxin-binding polypeptides and the investigation of their role in regulating plant development. Dr. Lomax has completed the purification of these very low abundance polypeptides. From the purified protein, she has obtained protein microsequence which has allowed her to design specific oligonucleotide probes. These probes will be used to select the corresponding cDNA clones encoding the 40 and 42kD auxin-binding polypeptides. The specific cDNA clones will be used 1) to determine the nucleic acid and amino acid sequence, 2) for functional expression studies, and 3) as probes for the study of transcriptional control and pattern of expression of the corresponding genes during development. The results of these studies should provide significant insight into both the structure and function of the putative symport protein and the role of IAA uptake in the regulation of growth and development in plants. The proposed studies will also forge a much needed link between the physiology and molecular biology of auxin action.
