Auxin signaling modulates LATERAL ROOT PRIMORDIUM1 (LRP1) expression during lateral root development in Arabidopsis

Abstract

Auxin signaling mediated by various Auxin/Indole-3-Acetic Acid (Aux/IAAs) and AUXIN RESPONSE FACTORs (ARFs) regulate lateral root (LR) development by controlling the expression of downstream genes. LATERAL ROOT PRIMORDIUM1 (LRP1), a member of SHORT INTERNODES/STYLISH (SHI/STY) family, was identified as an auxin inducible gene. Precise developmental role and molecular regulation of LRP1 in root development remains to be understood. Here we show that LRP1 is expressed in all stages of LR development, besides primary root. The expression of LRP1 is regulated by histone deacetylation in an auxin dependent manner. Our genetic interaction studies showed that LRP1 acts downstream of auxin responsive Aux/IAAs-ARFs modules during LR development. We showed that auxin mediated induction of LRP1 is lost in slr-1 and arf7arf19 mutants roots. NPA treatment studies showed that LRP1 acts after LR founder cell specification and asymmetric division. Overexpression of LRP1 (LRP1 OE) showed increased number of LRPs at stage I, IV and V, resulting in reduced emerged LR density, which suggests that it is involved in LRP development. Interestingly, LRP1 induced expression of YUC4, which is involved in auxin biosynthesis, contributes to increased accumulation of endogenous auxin in LRP1 OE roots. LRP1 interacts with SHI, STY1, SRS3 and SRS7 proteins of SHI/STY family indicating their possible redundant role during root development. Our results suggest that auxin and histone deacetylation affect LRP1 expression, and it acts downstream of LR forming auxin response modules to negatively regulate LRP development by modulating auxin homeostasis in Arabidopsis thaliana.