Different roles of Ca2+ and chitohexose in peanut (Arachis Hypogaea) photosynthetic responses to PAMP-immunity

Abstract

Background During active infections, plants prevent further spread of pathogenic microorganisms by inducing the rapid programmed death of cells around the infection point. This phenomenon is called the hypersensitive response and is a common feature of plant immune responses. Plants recognize conserved structures of pathogenic microorganisms, called pathogen-associated molecular patterns (PAMPs), e.g., flagellin 22 (flg22) and chitohexose, which bind to receptors on plant cells to induce various immune-response pathways. Although abiotic stresses are known to alter photosynthesis, the different effects of flg22 and chitohexose, which are involved into PAMP-induced signaling, on photosynthesis needs further study. Methods In the present study, we assessed the role of PAMPs in peanut (Arachis hypogaea) photosynthesis, particularly, the interaction between PAMPs and Ca2+ signal transduction pathway. Results Both flg22 and chitohexose significantly promoted the expression of the pathogenesis-related genes PR-4 and PR-10, as did Ca2+. We found that Ca2+ is involved in downregulating the photosystem II (PSII) reaction center activity induced by the flg22 immune response, but the role of chitohexose is not obvious. Additionally, Ca2+ significantly reduced the non-photochemical energy dissipation in the flg22- and chitohexose-induced immune response. Conclusion These results indicated that flg22 and chitohexose can trigger peanut immune pathways through the Ca2+ signaling pathway, but they differ in their regulation of the activity of the PSII reaction center.