Jasmonates regulate apical hook development by repressing brassinosteroid biosynthesis and signaling

Abstract

An apical hook is a special structure formed during skotomorphogenesis in dicotyledonous plant species. It is critical for protecting the shoot apical meristem from mechanical damage during seed germination and hypocotyl elongation in soil. Brassinosteroid (BR) and jasmonate (JA) phytohormones antagonistically regulate apical hook formation. However, the interrelationship between BRs and JAs in this process has not been well elucidated. Here, we reveal that JAs repress BRs to regulate apical hook development in Arabidopsis (Arabidopsis thaliana). Exogenous application of methyl jasmonate (MeJA) repressed the expression of the rate-limiting BR biosynthetic gene DWARF4 (DWF4) in a process relying on 3 key JA-dependent transcription factors, MYC2, MYC3, and MYC4. We demonstrated that MYC2 interacts with the critical BR-activated transcription factor BRASSINAZOLE RESISTANT 1 (BZR1), disrupting the association of BZR1 with its partner transcription factors, such as those of the PHYTOCHROME INTERACTING FACTOR (PIF) family and downregulating the expression of their target genes, such as WAVY ROOT GROWTH 2 (WAG2), encoding a protein kinase essential for apical hook development. Our results indicate that JAs not only repress the expression of BR biosynthetic gene DWF4 but, more importantly, attenuate BR signaling by inhibiting the transcriptional activation of BZR1 by MYC2 during apical hook development.

Interaction of the Transcription Factors BES1/BZR1 in Plant Growth and Stress Response

“…Additionally, they can interfere with the association between BZR1 and PIFs through the MYC2-BZR1 interaction. This disruption ultimately leads to the downregulation of WAG2 (Wavy Root Growth 2), a key kinase in apical hook formation, thus negatively impacting apical hook development [43].…”

PHB3 interacts with BRI1 and BAK1 to mediate brassinosteroid signal transduction in Arabidopsis and tomato

“…BRs regulate plant cell elongation and division, light sensing, vascular differentiation, flowering, male reproduction, and stress resistance (Clouse, 2011; Fabregas et al ., 2018; Gupta et al ., 2020). Moreover, BR regulates organ boundary determination, stomatal differentiation, root meristem maintenance, immune response, root hair formation, shoot branching, and leaf angle control in monocots (Shang et al ., 2016; Nolan et al ., 2017; Xia et al ., 2021; Zhang et al ., 2023).…”