WHIRLY1‐deficient chloroplasts display enhanced formation of cyclobutane pyrimidine dimers during exposure to UV‐B radiation

AbstractThe single‐stranded DNA/RNA binding protein WHIRLY1 is a major chloroplast nucleoid‐associated protein required for the compactness of nucleoids. Most nucleoids in chloroplasts of WHIRLY1‐knockdown barley plants are less compact compared to nucleoids in wild‐type plants. The reduced compaction leads to an enhanced optical cross‐section, which may cause the plastid DNA to be a better target for damaging UV‐B radiation. To investigate this hypothesis, primary foliage leaves, chloroplasts, and nuclei from wild‐type and WHIRLY1‐knockdown plants were exposed to experimental UV‐B radiation. Thereafter, total, genomic and plastid DNA were isolated, respectively, and analyzed for the occurrence of cyclobutane pyrimidine dimers (CPDs), which is a parameter for genome stability. The results of this study revealed that WHIRLY1‐deficient chloroplasts had strongly enhanced DNA damages, whereas isolated nuclei from the same plant line were not more sensitive than nuclei from the wild‐type, indicating that WHIRLY1 has different functions in chloroplasts and nucleus. This supports the hypothesis that the compaction of nucleoids may provide protection against UV‐B radiation.