NADPH-dependent thioredoxin reductase C plays a role in nonhost disease resistance against Pseudomonas syringae pathogens by regulating chloroplast-generated reactive oxygen species

Chloroplasts are cytoplasmic organelles for photosynthesis in eukaryotic cells. In addition, recent studies have shown that chloroplasts have a critical role in plant innate immunity against invading pathogens. Hydrogen peroxide is a toxic by-product from photosynthesis, which also functions as a signaling compound in plant innate immunity. Therefore, it is important to regulate the level of hydrogen peroxide in response to pathogens. Chloroplasts maintain components of the redox detoxification system including enzymes such as 2-Cys peroxiredoxins (2-Cys Prxs), and NADPH-dependent thioredoxin reductase C (NTRC). However, the significance of 2-Cys Prxs and NTRC in the molecular basis of nonhost disease resistance is largely unknown. We evaluated the roles of Prxs and NTRC using knock-out mutants of Arabidopsis in response to nonhost Pseudomonas syringae pathogens. Plants lacking functional NTRC showed enhanced bacterial growth and disease susceptibility in response to nonhost pathogens. Furthermore, the expression profiles of the salicylic acid (SA) and jasmonic acid (JA) -mediated signaling pathways and phytohormone analyses including SA and JA revealed that the Arabidopsis ntrc mutant is compromised in the regulatory cross-talk between the SA- and JA-mediated signaling pathways. These results suggest the critical role of NTRC in plant innate immunity against nonhost P. syringae pathogens.