Deciphering the Protein Phosphorylation Dynamics Triggered by Seconds of Force Stimulation

Area of Science:

• Plant Biology
• Mechanobiology
• Biochemistry

Background:

• Plants possess specialized phosphosignaling networks to perceive mechanical forces.
• The precise correlation between mechanical force signaling and gravity force signaling in plants remains largely unexplored.

Purpose of the Study:

• To elucidate the components of gravity force signaling in plants.
• To investigate the role of specific phosphoproteins and their dynamics in gravitropism.

Main Methods:

• SILIA-based phosphoproteomics was employed on Arabidopsis aerial organs subjected to inversion and gravistimulation.
• Spatiotemporal analysis and immunoblot validation were used to confirm phosphosite dynamics.
• Functional validation involved analyzing mutants of key regulatory proteins, such as GREPH1.

Main Results:

• Phosphoproteomics identified thousands of phosphoproteins, with distinct sets regulated by inversion and gravistimulation.
• Inversion-specific phosphoproteins are linked to initial calcium signaling, potentially involving EF-hand proteins, CPK1, and MAPK cascades.
• Gravistimulation-specific phosphoproteins are associated with secondary calcium signaling, membrane trafficking, and lipid signaling, supporting auxin transport and stress responses.
• The protein GREPH1 was identified as a key regulator of gravitropism, with its mutants exhibiting altered inflorescence stem gravicurvature and phosphosite phosphorylation dynamics.

Conclusions:

• A unique, stem-enriched phosphorylation mechanism is established for gravity force discrimination in plants.
• GREPH1 plays a critical role in modulating the spatiotemporal dynamics of phosphoproteins and shoot gravitropism.
• These findings provide insights into how plants perceive and respond to physical force signals, particularly gravity.