Abstract
A dominant Arabidopsis mutant, msg2, is defective in auxin-dependent growth curvature responses, but other aspects of growth and development are almost normal. MSG2 encodes an Aux/IAA protein, IAA19. Dominant Aux/IAA-gene mutations stabilize the encoded proteins, resulting in their accumulation in cells. In an attempt to elucidate a role of MSG2/IAA19 in tropic responses, we created many IAA19-overexpressing lines by the use of IAA19 full length cDNA under the control of CaMV35S promoter. One of them showed reduced gravitropism and phototropism in hypocotyl. It was also defective in root gravitropism, which is not observed in msg2. Northern-blot analysis showed that this line expressed IAA19 about 100-fold more than wild type. Another line displayed hyponastic leaves, which were also not observed in msg2. Comparing phenotype of msg2 and the transgeniclines, we will discuss significance of tissue specificity of IAA19 gene expression in specific defects characteristic in msg2 mutants.
