OsIAA1, an Aux/IAA cDNA from rice, and changes in its expression as influenced by auxin and light

The Aux/IAA class of genes are rapidly induced by exogenous auxins and have been characterized extensively from many dicot species like Arabidopsis, G lycine max and Pisum sativum. We report here the isolation and characteriza tion of rice (Oryza sativa L. subsp. Indica) OsIAA1 cDNA as a monocot membe r of the Aux/IAA gene family. The predicted amino acid sequence of OsIAA1 c orresponds to a protein of ca. 26 kDa, which harbors all four characteristi c domains known to be conserved in Aux/IAA proteins. The conservation of th ese Aux/IAA genes indicates that auxins have essentially a similar mode of action in monocots and dicots. Northern blot analysis revealed that the OsI AA1 transcript levels decrease in the excised coleoptile segments on auxin starvation, and the level is restored when auxin is supplemented; the incre ase in OSIAA1 transcript level was apparent within 15 to 30 min of auxin ap plication. Auxin-induced OsIAA1 expression appears to be correlated with th e elongation of excised coleoptile segments. In light-grown rice seedlings, OsIAA1 is preferentially expressed in roots and basal segment of the seedl ing, whereas in the etiolated rice seedlings, the OsIAA1 transcripts are mo st abundant in the coleoptile. A comparative analysis in light- and dark-gr own seedling tissues indicates that the OsIAA1 transcript levels decrease o n illumination.