the plant hormone auxin plays a central role in regulating many aspects of plant growth and development this largely occurs as a consequence of changes in gene expression the aux iaa genes are best characterized among the early auxin responsive genes which encode short lived transcriptional repressors in most plants examined including arabidopsis soybean and rice the aux iaa genes constitute a large gene family by screening the available databases at least 15 expressed sequence tags ests have been identified from wheat triticum aestivum which exhibit high sequence identity with aux iaa homologues in other species one of these aux iaa genes taiaa1 harbouring all the four conserved domains characteristic of the aux iaa proteins has been characterized in detail the expression of taiaa1 is light sensitive tissue specific and is induced within 15 30 min of exogenous auxin application also the taiaa1 transcript levels increase in the presence of a divalent cation ca 2 and this effect is reversed by the calcium chelating agent egta the taiaa1 gene qualifies as the primary response gene because an increase in its transcript levels by auxin is unaffected by cycloheximide in addition to auxin the taiaa1 gene is also induced by brassinosteroid providing evidence that interplay between hormones is crucial for the regulation of plant growth and development.