THE HAT4 GENE OF ARABIDOPSIS ENCODES A DEVELOPMENTAL REGULATOR

The HAT4 gene from the plant Arabidopsis thaliana encodes a homeo domain protein that contains a leucine zipper motif. Homeo domain-leucine zipper (HD-Zip) proteins have not been found in animal systems, suggesting that HAT4 may define a new family of transcription factors that regulate higher plant development. To explore this possibility, functional studies of HAT4 were carried out in yeast and in transgenic plants. Point mutants of HAT4 isolated in yeast define functionally critical residues within the HD-Zip domain, many of which correspond to highly conserved positions in known homeo domains and leucine zippers. Transgenic plants bearing constructs that alter HAT4 expression exhibit a series of interesting developmental phenotypes, including changes in morphology and developmental rate. Thus, the HAT4 gene of Arabidopsis encodes an HD-Zip protein that functions as a novel developmental regulator.