PHOSPHATASE 2A dephosphorylates PHYTOCHROME-INTERACTING FACTOR3 to modulate photomorphogenesis in Arabidopsis

Area of Science:

• Plant Biology
• Molecular Biology
• Biochemistry

Background:

• Phytochrome (phy) photoreceptors regulate plant development via light signaling.
• PHYTOCHROME-INTERACTING FACTORS (PIFs) are key transcription factors degraded upon light exposure.
• Kinases phosphorylate PIFs, but phosphatases involved in PIF dephosphorylation remain largely unknown.

Purpose of the Study:

• To identify phosphatases that dephosphorylate PIFs in Arabidopsis thaliana.
• To elucidate the role of specific Protein Phosphatase 2A (PP2A) subunits in PIF dephosphorylation and photomorphogenesis.

Main Methods:

• Yeast two-hybrid, in vitro, and in vivo assays to study protein interactions.
• Analysis of Arabidopsis mutants (pp2ab″αβ, b″αβ/b'αβ) and overexpression lines.
• RNA-sequencing to assess global gene expression changes.
• In vitro dephosphorylation assays using immunoprecipitated PP2A subunits and PIF3-MYC.

Main Results:

• Four PP2A regulatory subunits (B'α, B'β, B″α, B″β) interact with PIF3.
• Mutants lacking these subunits exhibit shorter hypocotyls under red light, while overexpression leads to longer hypocotyls.
• PIF3 degradation is accelerated in the quadruple mutant.
• PP2A subunits directly dephosphorylate PIF3 in vitro.
• B″α and B″β regulate global gene expression in response to red light.
• PIFs are epistatic to PP2A B subunits in hypocotyl elongation control.

Conclusions:

• PP2A regulatory subunits play a crucial role in dephosphorylating PIF3.
• This dephosphorylation is essential for modulating photomorphogenesis in response to red light.
• PP2A acts as a key regulator in the light signaling pathway impacting plant development.