Abstract
Lateral root (LR) formation in Arabidopsis is regulated by auxin signaling that depends on transcriptional activator Auxin Response Factors such as ARF7 and ARF19 and repressor auxin/indole-3-acetic acid (Aux/IAA) including IAA14/SOLITARY ROOT (SLR). In gain-of-function slr-1 mutant, stabilized IAA14 inactivates ARF7/19 functions and causes the block of LR initiation like arf7 arf19 double mutant. However, the mechanism of auxin-responsive transcription during LR formation is still unknown. Here, we show that MACCHI-BOU 2 (MAB2), which encodes MED13 subunit in a regulatory module of the Mediator complex, is required for the regulation of auxin-responsive transcription during LR formation. Genetic interaction between mab2 and slr-1 suggests that MAB2 negatively regulates LR formation. Furthermore, the mab2 mutation also restored expression of LBD16 and LBD29, which are direct targets of ARF7/19 in LR formation, in the slr-1 mutant backgrounds. These results indicate that MAB2 acts as a transcriptional repressor in coordination with IAA14 to inactivate ARF7/19 functions during LR formation.
