Plasmodesmata mediate cell-to-cell transport of brassinosteroid hormones

Abstract

Brassinosteroids (BRs) are steroidal phytohormones that are essential for plant growth, development, and adaptation to environmental stresses. BRs act in a dose-dependent manner and they do not travel over long distances, hence, BR homeostasis maintenance is critical for their function. Biosynthesis of bioactive BRs relies on cell-to-cell movement of hormone precursors. However, the mechanism of the short-distance BR transport is unknown and its contribution to control of endogenous BR levels remains unexplored. Here, we demonstrate that plasmodesmata (PD) mediate the passage of BRs between neighboring cells. Intracellular BRs content, in turn, is capable of modulating PD permeability to optimize its own mobility, thereby manipulating BR biosynthesis and signaling. Our work uncovers a thus far unknown mode of steroid transport in eukaryotes and exposes an additional layer of BR homeostasis regulation in plants.

Effects of a dark septate endophyte and extracellular metabolites on alfalfa root exudates: a non‐targeted metabolomics analysis

“…As a substrate, cholesterol promotes steroid hormone biosynthesis. BR stands for a class of steroid hormones that control plant development, growth, and environmental adaption and are crucial for plant development (Wang et al, 2023c). HM increases dolichyl diphosphate and promotes glycosylphosphatidylinositol (GPI)…”

Structure and function of the Arabidopsis ABC transporter ABCB19 in brassinosteroid export

“…1A). The ATPase activity of ABCB19 was activated by two other bioactive brassinosteroids with similar kinetic parameters, 24-epiBL and 24-epicastasterone (24-epiCS), but not by the brassinosteroid-biosynthesis precursors campesterol and 22-hydroxycampesterol (22-OHCR) ( 17 ) (fig. S1, B and C, and table S1) or by mammalian steroids such as cholesterol, taurocholic acid, and estrone sulfate (fig.…”

“…Next, we developed a transport assay for brassinosteroids in Arabidopsis protoplasts (Fig. 1D) using bio-orthogonal chemistry and the previously developed biologically active castasterone alkyne (CSA) ( 17 ). The castasterone isomer 24-epiCS stimulated the ATPase activity of ABCB19 (fig.…”

“…S1C), suggesting that castasterone is also a transport substrate. CSA was visualized by a click reaction between its alkyne and the azide group of the commercially available green-emitting fluorescent dye azide-BODIPY-fluorescein (azide-BDP-FL) to generate castasterone-BDP-FL ( 17 ). Arabidopsis protoplasts isolated from abcb19 single-mutant and WT plants were incubated with either CSA or dimethyl sulfoxide (DMSO) for 4 hours.…”

“…Brassinosteroid signaling is initiated in the apoplast by binding of a brassinosteroid molecule to the extracellular domain of the plasma membrane-localized receptor kinase BRAS-SINOSTEROID INSENSITIVE1 (BRI1) and coreceptor (1,(5)(6)(7)(8)(9)(10)(11)(12) to trigger downstream phosphorylation and dephosphorylation events that result in activation of the key transcription factors BRASSINAZOLE RESISTANT1 (BZR1) and BRI1-EMS-SUPPRESSOR1 (BES1)/BZR2, which regulate brassinosteroid-responsive genes (13,14). Although they are perceived at the cell surface, brassinosteroids are synthesized in the cell interior (15)(16)(17)(18), thus raising the ques-tion of how they reach the apoplast to bind their receptors. Because the bioactive brassinosteroids are polar molecules (19), they might not easily cross the membrane because of their hydrophilicity.…”