Light-induced global structural changes in phytochrome A regulating photomorphogenesis in plants.

Area of Science:

• Plant biology
• Biophysics
• Structural biology

Background:

• Phytochromes are crucial plant photoreceptors regulating growth and development by sensing light.
• They exist in two interconvertible forms, Pr (red-absorbing) and Pfr (far-red-absorbing), initiating signaling pathways.
• Understanding phytochrome structure is key to deciphering light-mediated plant responses.

Purpose of the Study:

• To determine the molecular structures of pea phytochrome A in its Pr and Pfr states.
• To investigate structural changes occurring during the Pr-to-Pfr phototransformation.
• To elucidate the mechanism of light signal transduction in plants.

Main Methods:

• Small-angle X-ray scattering (SAXS) was employed to study pea phytochrome A.
• A novel purification protocol ensured monodispersive sample solutions for SAXS analysis.
• Ab initio simulation methods were used to predict molecular structures from scattering data.

Main Results:

• SAXS data confirmed the dimeric association of pea phytochrome A in the Pr form.
• The predicted structure of Pr approximated a stack of two flat bodies with distinct lobes.
• Red-light irradiation induced subtle but significant structural changes in Pfr, suggesting domain movement.
• Structural changes in Pfr were reversible, primarily through thermal relaxation.

Conclusions:

• The study provides molecular insights into the structural rearrangements of phytochrome A during light-induced transformations.
• Global structural changes, including C-terminal domain movements, accompany the Pr-to-Pfr conversion.
• These findings contribute to understanding how plants perceive and respond to light signals.