Elongation and gravitropic responses of Arabidopsis roots are regulated by brassinolide and IAA

Abstract

Exogenously applied brassinolide (BL) increased both gravitropic curvature and length of primary roots of Arabidopsis at low concentration (10 -10 M), whereas at higher concentration, BL further increased gravitropic curvature while it inhibited primary root growth. BRI1-GFP plants possessing a high steady-state expression level of a brassinosteroid (BR) receptor kinase rendered the plant's responses to gravity and root growth more sensitive, while BR-insensitive mutants, bri1-301 and bak1, delayed root growth and reduced their response to the gravitropic stimulus. The stimulatory effect of BL on the root gravitropic curvature was also enhanced in auxin transport mutants, aux1-7 and pin2, relative to wild-type plants, and increasing concentration of auxin attenuated BL-induced root sensitivity to gravity. Interestingly, IAA treatment to the roots of bri1-301 and bak1 plants or of plants pretreated with a BL biosynthetic inhibitor, brassinazole, increased their sensitivity to gravity, while these treatments for the BL-hypersensitive transgenic plants, BRI1-GFP and 35S-BAK1, were less effective. Expression of a CYP79B2 gene, encoding an IAA biosynthetic enzyme, was suppressed in BL-hypersensitive plant types and enhanced in BL-insensitive or -deficient plants. In conclusion, our results indicate that BL interacts negatively with IAA in the regulation of plant gravitropic response and root growth, and its regulation is achieved partly by modulating biosynthetic pathways of the counterpart hormone.

RNA Interference Knockdown of BRASSINOSTEROID INSENSITIVE1 in Maize Reveals Novel Functions for Brassinosteroid Signaling in Controlling Plant Architecture

“…To further confirm disrupted BR signaling in zmbri1-RNAi lines, we performed a BR root growth inhibition assay, a commonly used bioassay for BR sensitivity (Clouse, 1996;Chono et al, 2003;Müssig et al, 2003;Kim et al, 2007;Wang et al, 2007;Hartwig et al, 2012). Germinated seeds were treated with distilled, deionized water (mock), 20 nM BL, or 100 nM BL.…”

Multiple Interactions between Glucose and Brassinosteroid Signal Transduction Pathways in Arabidopsis Are Uncovered by Whole-Genome Transcriptional Profiling

“…They have also been implicated to play a role in both biotic and abiotic stresses (Dhaubhadel et al, 1999(Dhaubhadel et al, , 2002Kagale et al, 2007;Koh et al, 2007;Xia et al, 2009). BRs also interact with auxin to regulate both root elongation and tropic responses in plants (Bao et al, 2004;Li et al, 2005;Kim et al, 2007).…”

Is kinase activity essential for biological functions of BRI1?

“…An allelic test in which the mutant was crossed with bri1-101, a strong allele of bri1 [13], showed that the mutant is allelic to bri1 (data not shown). Therefore, the mutant was designated bri1-301, which has been extensively used in the study of BR signaling pathways [14,18,[20][21][22].…”