Arabidopsis NF-YCs play dual roles in repressing brassinosteroid biosynthesis and signaling during light-regulated hypocotyl elongation

Apr 19, 2021The Plant cell

Arabidopsis NF-YC proteins reduce brassinosteroid production and response to control stem growth in light

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Abstract

Nuclear factor YC proteins (NF-YCs) are essential repressors of the brassinosteroid (BR) pathway during light-controlled hypocotyl growth in Arabidopsis thaliana.

In light conditions, NF-YCs inhibit the production of BR by directly suppressing the transcription of the BR biosynthesis gene BR6ox2.
NF-YCs also stabilize the repressor of BR signaling, BIN2, by promoting its autophosphorylation.
Loss-of-function mutants for NF-YCs exhibit elongated growth and constant BR responses, even in light.
These findings suggest that NF-YCs play a dual role in regulating both BR biosynthesis and signaling to support proper growth in response to light.

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Light functions as the primary environmental stimulus and brassinosteroids (BRs) as important endogenous growth regulators throughout the plant lifecycle. Photomorphogenesis involves a series of vital developmental processes that require the suppression of BR-mediated seedling growth, but the mechanism underlying the light-controlled regulation of the BR pathway remains unclear. Here, we reveal that nuclear factor YC proteins (NF-YCs) function as essential repressors of the BR pathway during light-controlled hypocotyl growth in Arabidopsis thaliana. In the light, NF-YCs inhibit BR biosynthesis by directly targeting the promoter of the BR biosynthesis gene BR6ox2 and repressing its transcription. NF-YCs also interact with BIN2, a critical repressor of BR signaling, and facilitate its stabilization by promoting its Tyr200 autophosphorylation, thus inhibiting the BR signaling pathway. Consistently, loss-of-function mutants of NF-YCs show etiolated growth and constitutive BR responses, even in the light. Our findings uncover a dual role of NF-YCs in repressing BR biosynthesis and signaling, providing mechanistic insights into how light antagonizes the BR pathway to ensure photomorphogenic growth in Arabidopsis.

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Arabidopsis NF-YCs play dual roles in repressing brassinosteroid biosynthesis and signaling during light-regulated hypocotyl elongation

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