Rice ferredoxin OsFd4 contributes to oxidative stress tolerance but compromises defense against blight bacteria

Ferredoxins (Fds) in plastids are the most upstream stromal electron receptors shuttling electrons to downstream metabolic systems and function in various physiological processes of dicots, but their roles in monocots’ response to stresses are still unclear. In this study, the functions of OsFd4, the major non-photosynthetic type Fd in rice, were characterized under oxidative stress and Xanthomonas oryzae pv. oryzae (Xoo) infection. OsFd4-knockout mutants displayed no defects in key agronomic traits and blast resistance, but were more sensitive to hydrogen peroxide (H₂O₂) treatment than the wild type. Transient expression of OsFd4 alleviated H₂O₂-induced rice cell death, suggesting that OsFd4 contributes to rice tolerance to exogenous oxidative stress. Deletion of OsFd4 enhanced rice immune responses against Xoo. OsFd4 formed a complex in vivo with itself and OsFd1, the major photosynthetic Fd in rice, and OsFd1 transcripts were increased in leaf and root tissues of the OsFd4-knockout mutants. These results indicate that OsFd4 is involved in regulating rice defense against stresses and interplays with OsFd1.