PROTEIN-PROTEIN INTERACTIONS AMONG THE AUX IAA PROTEINS/

The plant hormone indoleacetic acid (IAA) transcriptionally activates early genes in plants, The Aux/IAA family of early genes encodes prote ins that are short-lived and nuclear-localized. They also contain a pu tative prokaryotic beta alpha alpha DNA binding motif whose formation requires protein dimerization, Here, we show that the pea PS-LAM and A rabidopsis IAA1 and IAA2 proteins perform homo- and heterotypic intera ctions in yeast using the two-hybrid system, Gel-filtration chromatogr aphy and chemical cross-linking experiments demonstrate that the PS-IA A4 and IAA1 proteins interact to form homodimers in vitro. Deletion an alysis of PS-IAA4 indicates that the beta alpha alpha containing acidi c C terminus of the protein is necessary for homotypic interactions in the yeast two-hybrid system, Screening an Arabidopsis lambda-ACT cDNA library using IAA1 as a bait reveals heterotypic interactions of IAA1 with known and newly discovered members of the Arabidopsis Aux/IAA ge ne family, The new member IAA24 has similarity to ARF1, a transcriptio n factor that binds to an auxin response element, Combinatorial intera ctions among the various members of the Aux/IAA gene family may regula te a variety of late genes as well as serve as autoregulators of early auxin-regulated gene expression. These interactions provide a molecul ar basis fur the developmental and tissue-specific manner of auxin act ion.