# Role of CIA2 and CIL in the Regulation of Chloroplast Development During Photomorphogenesis in Arabidopsis

## TL;DR

This study shows that CIA2 and CIL proteins are important for chloroplast development in plants, especially during the transition from dark to light conditions.

## Contribution

The study reveals CIA2 as the dominant factor in regulating chloroplast development and function during photomorphogenesis.

## Key findings

- CIA2 and CIL affect chloroplast ultrastructure, pigment accumulation, and photosynthetic gene expression.
- Complementation with CIA2 restores chloroplast morphology and function in mutant plants.
- CIA2 and CIL contribute to plant responses to light stress and chloroplast biogenesis.

## Abstract

What are the main findings?
CIA2 and CIL participate and optimize chloroplast biogenesis and development, affecting chloroplast ultrastructure, pigment accumulation, PSII function, and expression of key photosynthetic and protein-import genes.Complementation of the double cia2cil mutant with functional CIA2 restores early greening, chloroplast morphology, PSII performance, and gene expression dynamics to near wild-type levels, revealing CIA2 as the dominant factor in this regulatory module.

CIA2 and CIL participate and optimize chloroplast biogenesis and development, affecting chloroplast ultrastructure, pigment accumulation, PSII function, and expression of key photosynthetic and protein-import genes.

Complementation of the double cia2cil mutant with functional CIA2 restores early greening, chloroplast morphology, PSII performance, and gene expression dynamics to near wild-type levels, revealing CIA2 as the dominant factor in this regulatory module.

What is the implication of the main finding?
The results suggest that CIA2 and CIL may contribute not only in the regulation of responses to UV-AB, high light, heat shock and chloroplast translation regulation as it was indicated before, but also play a role in establishment of functional chloroplasts during early development, providing a basis for future studies for amelioration of crops chloroplast performance and photosynthetic capacity and in general plant light stress responses.

The results suggest that CIA2 and CIL may contribute not only in the regulation of responses to UV-AB, high light, heat shock and chloroplast translation regulation as it was indicated before, but also play a role in establishment of functional chloroplasts during early development, providing a basis for future studies for amelioration of crops chloroplast performance and photosynthetic capacity and in general plant light stress responses.

Chloroplast development plays a crucial role in plant de-etiolation, a process in which plants switch from growth in darkness to light-driven development, known as photomorphogenesis. This study provides evidence that CIA2 (Chloroplast Import Apparatus 2) and CIL (CIA2-Like) contribute to chloroplast biogenesis, likely by affecting and regulating PSII activity and related gene expression. Although their precise molecular roles remain unclear, our findings support their possible involvement in chloroplast development. This is indicated by downregulation of foliar chlorophyll content, chlorophyll a fluorescence parameters, chloroplast size, and gene expression of PSII molecular markers in the cia2cil double mutant during de-etiolation. Chlorophyll a fluorescence and quantitative gene expression analysis during de-etiolation revealed a significant reduction in PSII maximal efficiency and non-photochemical quenching, as well as deregulated expression of genes such as LHCB2.1 and psbA. According to the immunoblotting and microscopy imaging results, there is an impaired function of PSII and a compromised ultrastructure of the chloroplast membranes in cia2cil plants. However, in CIA2p::CIA2cia2cil and 35Sp::CIA2cia2cil complementation lines, reversion of this phenotype was observed. These results suggest a supporting role for CIA2 and CIL in the plant de-etiolation process, expanding our understanding of chloroplast biogenesis regulation.