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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Crop Diseases, Pests and Genetics Research » Research » Publications at this Location » Publication #430384
Research Project: Identifying Vulnerabilities in Vector-host-pathogen Interactions of Grapevine and Citrus Pathosystems to Advance Sustainable Management Strategies

Location: Crop Diseases, Pests and Genetics Research

Title: Optimal brassinosteroid homeostasis is required to maximize Arabidopsis hypocotyl growth in the dark

Author
item Peng, Hao
item Zhai, Ying

Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2025
Publication Date: 11/27/2025
Citation: Peng, H., Zhai, Y. 2025. Optimal brassinosteroid homeostasis is required to maximize Arabidopsis hypocotyl growth in the dark. Biochemical and Biophysical Research Communications. Available online. https://doi.org/10.1016/j.bbrc.2025.153062.
DOI: https://doi.org/10.1016/j.bbrc.2025.153062

Interpretive Summary: Brassinosteroids (BRs) are a group of plant hormones that are crucial for plant growth and adaptation to environmental conditions. During seed germination, BRs can modulate stem elongation, whose length affects seedling ability to push through the soil and reach light. Manipulation of BR stability in crops may improve their deep sowing capacity to confer drought tolerance. However, BRs' effects on stem growth depend on light conditions, and it is still unclear how BRs modulate stem elongation in the dark. In this research, we used the model plant species Arabidopsis and its BR-deficient mutants generated by overexpressing grapevine gene CYP734A15 to test their stem growth response to treatments of BRs and the BR biosynthesis inhibitor brassinazole (BRZ). The results demonstrated that optimal BR accumulation is required to maximize plant stem growth in the dark.

Technical Abstract: Plants produce a group of steroid hormones named brassinosteroids (BRs), with brassinolide (BL) and castasterone (CS) exhibiting highest biological activity. The maintenance of appropriate BR homeostasis is crucial for plant growth and adaptation to environmental conditions. BRs negatively regulate Arabidopsis thaliana seedling photomorphogenesis by promoting hypocotyl elongation in the light. However, both BL and the BR biosynthesis inhibitor brassinazole (BRZ) suppress Arabidopsis hypocotyl growth in the dark, indicating a seemingly contradictory role of BRs in seedling skotomorphogenesis. Using wild-type Col-0 and two independent BR-deficient mutants previously generated by ectopically overexpressing the grapevine BR-inactivating enzyme CYP734A15 in Arabidopsis, we quantified dark-grown hypocotyl length changes in response to BL or BRZ treatments at a wide range of concentrations. The results revealed that BR homeostasis in wild-type Arabidopsis seedlings is nearly optimal yet slightly excessive for achieving maximal hypocotyl growth in the dark. Gentle BRZ treatments slightly reduce seedling BR levels to maximize hypocotyl growth. Treatments with BL and higher concentrations of BRZ suppress hypocotyl growth via distinct mechanisms of overdosing BRs to toxic levels and further reducing BRs to insufficient levels, respectively. For dark-grown BR-deficient mutants, mild BL treatments boosted their BR levels to promote hypocotyl growth, whereas further increases of BL supply were overdosed for hypocotyl growth. BRZ treatments on BR-deficient mutants further reduced the already insufficient BR levels, making their hypocotyls even shorter. In conclusion, optimal BR homeostasis is required to maximize Arabidopsis hypocotyl growth in the dark.