Aux/IAA proteins are phosphorylated by phytochrome in vitro

Area of Science:

• Plant Biology
• Molecular Biology
• Genetics

Background:

• Auxin/indole-3-acetic acid (Aux/IAA) genes encode transcription factors crucial for plant development.
• Gain-of-function mutations in Aux/IAA genes lead to enhanced auxin responses and altered photomorphogenesis.
• Previous studies suggested a link between Aux/IAA mutations and phytochrome-independent light responses.

Purpose of the Study:

• To investigate the direct interaction between Aux/IAA proteins and phytochrome.
• To determine if phytochrome phosphorylates Aux/IAA proteins.
• To elucidate the molecular mechanism integrating auxin and light signaling.

Main Methods:

• In vitro interaction assays using recombinant proteins.
• In vitro phosphorylation assays with recombinant phytochrome A and Aux/IAA proteins.
• Metabolic labeling and immunoprecipitation studies in vivo.
• Deletion analysis of Ps-IAA4 to map phosphorylation sites.

Main Results:

• Recombinant Aux/IAA proteins from Arabidopsis and pea interact with oat phytochrome A in vitro.
• Oat phytochrome A phosphorylates several recombinant Arabidopsis and pea Aux/IAA proteins.
• Phytochrome A phosphorylation sites on Ps-IAA4 are located in the N-terminal half.
• Mutant IAA3 protein levels are increased, and SHY2-2 protein is phosphorylated in vivo in shy2-2 plants.

Conclusions:

• Phytochrome A directly interacts with and phosphorylates Aux/IAA proteins.
• Phytochrome-dependent phosphorylation of Aux/IAA proteins is a novel mechanism for integrating auxin and light signaling.
• This cross-talk between signaling pathways provides a molecular basis for developmental plasticity in plants.