Chlorophyll deficient barley xan-n mutants are defective in an essential superoxide dismutase

The differentiation of proplastids into chloroplasts is driven by light and closely linked to the process of chlorophyll biosynthesis. Chloroplasts, while essential for photosynthesis, also generate reactive oxygen species (ROS), necessitating robust antioxidant mechanisms such as superoxide dismutases (SODs). SODs catalyze the detoxification of superoxide radicals to molecular oxygen and hydrogen peroxide. The three types of superoxide dismutase in plant cells are classified based on their active site metal ion (iron, manganese or copper/zinc). In the present study, we analyzed a set of three allelic barley xan-n mutants, which are characterized by a lethal and pale phenotype due to a lack of chlorophyll. Using bulk-segregant analysis of a xan-n F₂-mapping population, we identified xan-n as encoding a chloroplastic FeSOD (HORVU.MOREX.r3.7HG0640950) orthologous to Arabidopsis FSD2. The three mutations impact the protein's ability to manage oxidative stress, leading to defective chloroplasts. Comparative analyses across plant species revealed a conserved function of FeSODs in chloroplast development. This study highlights the importance of FeSODs in chlorophyll biosynthesis and provides insights into the genetic and functional diversity of these enzymes in plants.