GERALT, a cryptochrome/photolyase family protein, is essential for young chloroplast development and function with its importance decreasing in older plants

Many proteins belonging to the cryptochrome/photolyase family play important roles in regulating plant functions, acting either as blue-light photoreceptors or as enzymes responsible for the repair of pyrimidine dimers produced under UV light. The members of the plant-specific photolyase/blue-light receptor 2 (PPL/PHR2) subclade of this family are almost completely uncharacterized. Here, we focused on the role of the protein encoded by the Arabidopsis At2g47590 gene. Mutants in this gene have albino cotyledons, pale green true leaves and drastically delayed development. Based on these features, we named the At2g47590 gene: GERALT (GERMINATION ALBINO TRANSIENT). Using different approaches including analysis of plant phenotypes, chloroplast sizes and architecture, transcriptomes, photosynthetic pigments, and maximum PSII quantum yield (FV/FM), we show that proper plant functioning is the effect of co-operation of GERALT-dependent and -independent pathways with the role of the former diminishing with plant age. Lower levels of transcripts dependent on plastid-encoded polymerase and higher levels of these dependent on the nuclear-encoded polymerase, smaller chloroplasts with large grana stacks and very weakly developed stromal thylakoids, and lower levels of photosynthetic pigments with higher chlorophyll a/b ratio are among the characteristic features of geralt plants. We believe that these results will encourage the scientific community to study PPL/PHR2 proteins.