DEVELOPMENTAL AND AUXIN-INDUCED EXPRESSION OF THE ARABIDOPSIS-PRHA HOMEOBOX GENE

A single-copy Arabidopsis homeobox gene, prha, which encodes a homeodo main protein with a molecular weight of 90 500 has been characterized. The position of the gene was mapped to the distal part of chromosome 4. Expression of the gene differs in various vegetative and floral pla nt tissues and is positively influenced by the phytohormone auxin. In Arabidopsis plants, a complex pattern of prha promoter-driven GUS expr ession is observed, often associated with regions of developing vascul ar tissue. Exogenously applied auxin strongly increased endogenous prh a transcript levels. In addition, the prha promoter is highly responsi ve to the synthetic auxin, naphthalene acetic acid, in transient assay s using tobacco protoplasts. The PRHA protein has the capacity to bind to TAATTG core sequence elements but requires additional adjacent bas es for high-affinity binding. These findings are discussed in relation to studies of other plant homeobox genes as well as possible in vivo target genes for PRHA.