Unraveling Brassinosteroid Biosynthesis: Orchestrating BR Precursor Movement via Endoplasmic Reticulum-Plasma Membrane Contact Sites (EPCSs)

Since their discovery in 1979, brassinosteroids (BRs) have been extensively studied for their biosynthesis and signalling pathways. Now, in the year 2023, one fundamental question remains: how do BRs move?

As the only type of steroidal phytohormones essential for plant growth and development, BRs act in a dose-dependent manner and do not travel long distances. Therefore, BR homeostasis is key to their function.

Recent findings in my host lab revealed that in the Arabidopsis root the expression domains of BR biosynthetic enzymes are separated, and the completion of BR biosynthesis requires cell-to-cell movement of precursors, thus, revealing the importance of the short-distance transport for BR homeostasis maintenance.

Further we revealed that plasmodesmata (PD) mediate the passage of BRs between neighbouring cells.

However, we still do not know where in the cell BRs are synthesized and how these hydrophobic molecules are moving through PD.

By searching interactors of BR biosynthetic enzymes, my host lab found interesting candidates associated with the endoplasmic reticulum (ER)-plasma membrane (PM) contact sites (EPCSs), including PD. EPCSs are known lipid synthesis platforms and contribute to PD function in plants. Here, I hypothesize that BRs are synthesized at EPCSs, and EPCSs coordinate BR biosynthesis and transport through PD.

In BRACTION, I will combine live cell imaging with state-of-the-art imaging techniques to pinpoint BR biosynthesis sites in the cell.

Combining advanced proteomics, genetics, and biochemistry, I aim to identify novel candidates that regulate BR biosynthesis and movement linked to EPCSs.

Finally, I will employ genetics combined with bioorthogonal chemistry approach to assess candidate influence on BR symplastic movement.

BRACTION's interdisciplinary approach will address knowledge gaps in BR homeostasis and drive major conceptual advances in understanding how BR levels are maintained across different cell types and tissues.