A Chimeric Peptide for Shielding Plant Photosynthetic\nSystems against Excess Light Stress via Chloroplast-Targeted ROS Quenching

The ability to quench\nreactive oxygen species (ROS) overproduced\nin plant chloroplasts under light stress conditions is essential for\nsecuring plant photosynthetic performance and agricultural yield.\nAlthough genetic engineering can enhance plant stress resistance,\nits widespread application faces limitations due to challenges in\nsuccessful transformation across plant species and public acceptance\nconcerns. This study proposes a nontransgenic chemical approach using\na designed chimeric peptide that scavenges ROS within plant chloroplasts\nfor managing light stress. The chimeric peptide was strategically\ndesigned by combining cell-penetrating and chloroplast-targeting sequences,\neach with antioxidant ability against destructive ROS such as hydroxyl\nradical (•OH) and singlet oxygen (<sup>1</sup>O<sub>2</sub>). Our analyses involving various cell-penetrating peptides and a\nchloroplast-targeting peptide revealed that the •OH-scavenging\nability predominantly relied on side chain oxidation in tryptophan\nresidues, while the <sup>1</sup>O<sub>2</sub>-quenching capacity was\nattributed to the oxidation of cysteine and methionine side chains.\nWe further demonstrated that the chimeric peptide could traverse the\ncell wall and membranes to reach chloroplasts, where it scavenged\n•OH and <sup>1</sup>O<sub>2</sub> and alleviated light-stress-induced\nchlorophyll degradation in leaves. Foliar spraying of the peptide\nsuccessfully protected photosynthetic activity in leaves exposed to\nexcessive light, highlighting its potential for practical agricultural\napplications. This work can offer a promising approach for managing\nabiotic stress without genetic modifications and provide valuable\ninsights into the design of effective peptide-based ROS quenchers\nspecifically targeting plant chloroplasts.