Abstract
SummaryBrassinosteroids (BRs) play crucial roles in plant development, but little is known of mechanisms that integrate environmental cues into BR signaling. Conjugation to the small ubiquitin-like modifier (SUMO) is emerging as an important mechanism to transduce environmental cues into cellular signaling. In this study, we show that SUMOylation of BZR1, a key transcription factor of BR signaling, provides a conduit for environmental influence to modulate growth during stress. SUMOylation stabilizes BZR1 in the nucleus by inhibiting its interaction with BIN2 kinase. During salt stress, Arabidopsis plants arrest growth through deSUMOylation of BZR1 in the cytoplasm by promoting the accumulation of the BZR1 targeting SUMO protease, ULP1a. ULP1a mutants are salt tolerant and insensitive to the BR inhibitor, brassinazole. BR treatment stimulates ULP1a degradation, allowing SUMOylated BZR1 to accumulate and promote growth. This study uncovers a mechanism for integrating environmental cues into BR signaling to shape growth.
Highlights
Plants are constantly challenged with various environmental stresses during their life cycle
We show that SUMOylation of BZR1 provides a conduit for environmental influence on BR signaling to modulate growth under salt stress
We identified the Arabidopsis small ubiquitin-like modifier (SUMO) protease mutant, ulp1a [36], which showed increased seedling root growth when compared to Col-0 under salt stress (Figures 1A, 1B, 1E, S1A, and S1B)
Summary
Plants are constantly challenged with various environmental stresses during their life cycle. In absence or low levels of BRs, BIN2 is predominantly dephosphorylated and activated to phosphorylate two homologous transcription factors, BZR1 and BES1, and cause their cytoplasmic retention, where they are targeted for degradation by proteasome [16,17,18,19]. BZR1 and BES1 are dephosphorylated by a protein phosphatase PP2A [21] and move into the nucleus, where they bind to promoters of target genes, leading to the expression of the BR-regulated genes that enact physiological responses in plants [22,23,24,25]. Evidence to date indicates that, after perception of BRs, the inactivation of BIN2 that targets BZR1/BES1 transcription factors remains the major point of regulation in BR signaling. Little is known of the critical steps that facilitate BIN2 interaction with these transcription factors that determines BR signaling in plants
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