Developmental and auxin-induced expression of the Arabidopsis prha homeobox gene

A single-copy Arabidopsis homeobox gene, prha, which encodes a homeodomain 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 plant tissues and is positively influenced by the phytohormone auxin. In Arabidopsis plants, a complex pattern of prha promoter-driven GUS expression is observed, often associated with regions of developing vascular tissue. Exogenously applied auxin strongly increased endogenous prha transcript levels. In addition, the prha promoter is highly responsive to the synthetic auxin, naphthalene acetic acid, in transient assays using tobacco protoplasts. The PRHA protein has the capacity to bind to TAATTG core sequence elements but requires additional adjacent bases 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.