Physiological and Molecular Studies on the Chitosan-N Confers Anti-PRSV Ability of Carica Papaya L.

Prevention and control of papaya ringspot virus (PRSV) is a difficult problem for papaya growers all over the world. CTS-N (Chitosan-N) can alleviate viral pathogenesis by inducing defense-related enzymatic activities. In this study, we quantified superoxide anion production, assayed the activities of defense enzymes (POD, PPO, SOD, and chitinase), and measured the contents of key phytohormones (ETH, JA, SA, and ABA). Based on transcriptomic data from our preliminary work, the full-length CpRBOHD gene was cloned using RACE (Rapid amplification of cDNA ends). A plant overexpression vector was subsequently constructed and agroinfiltrated into PRSV-infected papaya leaves. Expression dynamics of CpRBOHD were analyzed by qPCR, and concomitant changes in physiological indices were evaluated. The application of 1.0 g/L CTS-N significantly enhanced defense enzyme activities and elevated phytohormone levels. The coding sequence (CDS) of the CpRBOHD gene was 2760bp. Transient overexpression of CpRBOHD in PRSV-infected leaves resulted in a marked upregulation of its expression, as confirmed by qPCR. This was accompanied by increased activities of SOD, CAT, and PAL, alongside a reduction in MDA content. These findings indicate that increased CpRBOHD expression is associated with enhanced resistance to PRSV. The identification of PRSV-responsive genes represents a promising strategy for breeding resistant cultivars. Collectively, our results provide a theoretical basis for the biological control of papaya ringspot disease.