Abstract
The solitary-root (slr) mutants in Arabidopsis, which have gain-of-function mutations in IAA14, have no lateral roots (LRs). It is suggested that the mutant IAA14 protein (mIAA14) might repress the activity of Auxin Response Factors (ARFs) that promote LR formation. To understand the relationship between tissue-specific auxin response and root morphogenesis, we analyzed the transgenic plants expressing the mIAA14-GR (glucocorticoid receptor) fusion protein under tissue-specific promoters. DEX-treated transgenic plants expressing mIAA14-GR under the IAA14 promoter showed the slr phenotypes, indicating that mIAA14-GR is functional. We found that expression of mIAA14-GR under the stele-specific promoter (SHORT-ROOT) suppresses LR initiation, indicating that auxin response in stele is important for LR initiation. On the other hand, expression of mIAA14-GR under the SCARECROW promoter (expressed in the specific cells during LR primordium development) caused the formation of LR primordia with abnormal organization. This result indicates that auxin response is also important during LR primordium development.
