brassinosteroid
Brassinosteroids are a class of polyhydroxysteroid plant hormones that regulate key developmental processes including stem elongation, cell division, and overall growth. As the sixth recognized class of plant hormones, they play critical roles in stress responses, germination, and reproductive development, making them important targets for research aimed at improving crop yield and resilience. Their ability to modulate growth pathways has also drawn interest for potential applications in agricultural biotechnology.
open_in_new WikipediaPubMed · 2026-04-15
Scientists identified a protein called OsbHLH55 that controls how much rice leaves angle outward from the stem — a trait directly tied to how densely farmers can plant crops and how much sunlight each plant captures for maximum yield.
Rice plants with the OsbHLH55 gene deleted showed significantly larger leaf inclination angles due to increased parenchyma cell size at the leaf joint, while plants engineered to overproduce the protein showed smaller angles.
OsbHLH55 is directly suppressed by brassinosteroid (a plant growth hormone), and mutant plants lacking it were hypersensitive to brassinosteroid — placing OsbHLH55 as a negative regulator in the brassinosteroid signaling pathway.
OsbHLH55 physically binds to the promoter of another gene (OsWRKY53) to silence it, and is itself chemically modified (phosphorylated) by a stress-signaling enzyme (OsMAPK6), revealing a new molecular pathway linking hormone and stress signaling in leaf architecture.
