Light and brassinosteroids modulate Arabidopsis seedling root growth in a largely independent manner

Authors: Peng, Hao; Zhai, Ying

Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2026
Publication Date: 2/27/2026
Citation: Peng, H., Zhai, Y. 2026. Light and brassinosteroids modulate Arabidopsis seedling root growth in a largely independent manner. Biochemical and Biophysical Research Communications. 810. https://doi.org/10.1016/j.bbrc.2026.153538.
DOI: https://doi.org/10.1016/j.bbrc.2026.153538

Interpretive Summary: Brassinosteroids (BRs) are plant hormones that modulate growth and development of plant shoots and roots. BRs are well known to promote shoot elongation in the light. However, little is known about BRs' accurate role in root elongation and the possible involvement of light. In this research, we used the model plant Arabidopsis to test plant root response to treatments of either Brassinolide or the BR biosynthesis inhibitor brassinazole. Plants tested included wild type, a BR-overproducing mutant, and two BR-deficient mutants. Results indicate that light and BRs promote and inhibit root growth, respectively, acting on root elongation in a largely independent manner. These findings provide guidance for future BR applications to crops. While BR application by spray can promote shoot growth and biomass accumulation, the dose should be carefully controlled to minimize negative impact on root growth.

Technical Abstract: Brassinosteroids (BRs) are a class of steroid phytohormones that promote plant growth and tolerance to both biotic and abiotic stress. BAS1/CYP734A1, SOB7/CYP72C1, and BEN1 are three BR-inactivating enzymes characterized in Arabidopsis thaliana. The triple-null mutant bas1-2 sob7-1 ben1-3 exhibits strong BR-overproducing phenotypes. The CYP734A cytochrome P450 protein family is highly conserved across plant species. Ectopic overexpression of grapevine CYP734A15 in Arabidopsis causes severe BR-deficient phenotypes. BRs differentially modulate hypocotyl growth in photomorphogenic and skotomorphogenic seedlings. However, little is known about the potential involvement of light in BR-regulated seedling root growth. In this research, we grew Arabidopsis seedlings of the wild-type (WT) Col-0, the BR-overproducing mutant bas1-2 sob7-1 ben1-3, and two BR-deficient CYP734A15 overexpression mutants CYP734A15ox-3 and CYP734A15ox-4 in either continuous white light or constant darkness, with treatments of either brassinolide (BL, the most bioactive, naturally occurring BR) or the BR biosynthesis inhibitor brassinazole (BRZ) at a wide range of concentrations. Primary root length measurement results showed that light promoted seedling root growth regardless of endogenous BR levels. Both endogenous and exogenous BRs suppressed seedling root growth independently of light. BRZ treatments also suppressed root elongation in light-grown seedlings regardless of endogenous BR levels, probably due to its toxic effects. In the dark, BRZ still slightly suppressed root elongation in CYP734A15ox-3/4 seedlings but the effect switched to moderate promotion for roots growth in Col-0 and bas1-2 sob7-1 ben1-3. Collectively, our work suggests that light and BRs differentially modulate Arabidopsis seedling root growth in a largely independent manner.