Interaction among BREVIPEDICELLUS, BLH6 and auxin in roots of Arabidopsis thaliana

Abstract

Three-amino-acid-loop-extension homeodomain proteins affect various aspects during root development, such as root skewing or lateral root initiation and growth. Crossed lines of the BP overexpressor in Arabidopsis thaliana (L.) Heynh. were used to elucidate the role of BREVIPEDICELLUS (BP) in root development. The potential heterodimerization partner of BP, BEL1-like homeodomain protein 6 (BLH6), could be an important modulator of BP function. BLH6 is a member of BEL-like family of homeodomain proteins consisting of all conserved domains and motifs. We identified a new BLH-specific TERM motif at the C terminus of BLH proteins. BLH6 was expressed in different root tissues, including the meristematic zone and bases of lateral roots, and overlap the BP expression zone, enabling coordinated function of these transcription factors. To elucidate potential interactions of BP and BLH6, crossed lines of BP overexpressor were analyzed. While other tested BLH mutations do not affect BP overexpression phenotype, knock-out mutation blh6-1 weakened 35S-BP influence on shoot and root development. We demonstrated that growth of lateral roots was modulated by BP overexpression and auxins, and that this effect was dependent on lateral root position along the primary root. In the upper part of the primary root, BP inhibited lateral root growth despite indol-3-acetic acid treatment and this effect correlated with predicted activity of BLH6 in crossed lines of 35S-BP and blh6 mutants.