# A red/blue optoswitch for temporal control of chloroplast transcription and biogenesis in Arabidopsis

## TL;DR

Scientists created a light-controlled switch to restore chloroplast development in a mutant plant, revealing new insights into plant biology.

## Contribution

A red/blue optoswitch is developed to control chloroplast transcription and biogenesis in Arabidopsis.

## Key findings

- A blue-light-induced PAP7 construct rescues non-viable albino mutants by restoring PEP activity.
- Chloroplast biogenesis is only inducible in very young leaf tissues.
- Initial PEP formation and function are independent of photosynthesis.

## Abstract

Photosynthesis genes in plant chloroplasts are transcribed by the plastid-encoded RNA polymerase called PEP. Consequently, PEP-deficient mutants cannot generate a photosynthetic apparatus and develop non-viable albino seedlings. Inducible complementation of such mutants thus could provide interesting insights in PEP action and chloroplast biogenesis. Here we show the effects of photo-inducible complementation in the albino Arabidopsis mutant pap7-1 using a red/blue optoswitch with monochromatic LEDs. Expression of a blue-light-induced PAP7 construct that is silent under red light reconstitutes PEP at any time point of pap7-1 development resulting in proper chloroplast biogenesis that rescues the non-viable mutant. Induction of chloroplast biogenesis, however, can only occur in very young leaf tissues indicating the existence of a cell-autonomous, biogenic coupling between cell and organelle development. We further uncover that initial PEP formation and function is independent of photosynthesis. The optoswitch termed blue-light valved biogenesis opens experimental avenues to study non-viable plant mutants.

Plants require the plastid encoded RNA polymerase PEP to generate viable photosynthetic apparatus. Here the authors genetically engineer an optoswitch that enables photo-induced complementation of an albino mutant restoring transcription and chloroplast biogenesis on demand.