Work

Role of photolyase in stress tolerance and virulence of plant-pathogenic bacterium Pseudomonas cichorii JBC1

Year: 2026

Type: article

Abstract: ABSTRACT The cryptochrome/photolyase family (CPF) comprises structurally conserved flavoproteins with diverse roles in light-dependent DNA repair and stress adaptation. Here, we identified and functionally characterized a class I cyclobutane pyrimidine dimer (CPD) photolyase, Pc-Phr, from the plant-pathogenic bacterium Pseudomonas cichorii JBC1 (PcJBC1). Spectroscopic analyses revealed that Pc-Phr binds flavin adenine dinucleotide (FAD) and undergoes characteristic blue light–induced photoreduction from the oxidized state (FAD OX ) to catalytically active reduced forms. Pc-Phr exhibited robust photoreactivation activity, repairing UV-induced CPDs in vitro and restoring the viability of UV-C–irradiated cells in vivo , whereas this activity was abolished in a phr deletion mutant. Transcriptional analyses showed that phr expression is induced by UV-C and further enhanced by blue light, consistent with a light-dependent DNA damage response. Beyond DNA repair, Pc-Phr promoted bacterial survival, growth, and adhesion under UV-C, high-intensity blue light, and oxidative stress conditions, and was essential for maintaining intracellular reactive oxygen species (ROS) homeostasis. Deletion of phr resulted in a drastic ROS accumulation and significantly reduced survival under both UV-C and H 2 O 2 stress. Importantly, Pc-Phr contributed to virulence in host plants, with the mutant exhibiting markedly reduced pathogenicity. These results demonstrate that efficient photorepair is a critical determinant of environmental fitness and pathogenicity in P. cichorii , highlighting the importance of light-responsive DNA repair systems in plant-associated bacteria. IMPORTANCE Plant-pathogenic bacteria must withstand environmental stresses such as ultraviolet radiation and host-derived oxidative bursts to survive and cause disease. Although photolyases are well known for repairing UV-induced DNA lesions, their broader roles in bacterial physiology and pathogenicity remain insufficiently understood. This study demonstrates that the photolyase Pc-Phr in Pseudomonas cichorii not only facilitates efficient repair of UV-induced DNA but also plays a critical role in maintaining intracellular redox balance. Loss of Pc-Phr led to excessive accumulation of ROS, increased sensitivity to environmental stress, and reduced bacterial fitness. Importantly, Pc-Phr contributes to virulence-associated traits, including adhesion to host surfaces, colonization, and survival in planta, revealing a direct link between photoreactivation, oxidative stress tolerance, and pathogenicity. These findings expand the functional scope of photolyases beyond genome maintenance and reveal their significance in environmental adaptation and plant-microbe interactions.

Source: Applied and Environmental Microbiology

DOI: 10.1128/aem.00255-26

Authors: Nguyen Van Khanh, Shamjetsabam Gangarani Devi, Yong Hoon Lee

Institution: Jeonbuk National University

Language: English

Topic: Plant Pathogenic Bacteria Studies

Subfield: Plant Science

Field: Agricultural and Biological Sciences

Domain: Life Sciences

Open Access status: diamond

Funder: National Research Foundation of Korea

Award: G4954469192