Extraction optimization, physicochemical properties, and inhibitory effect against tobacco mosaic virus of the protein from discarded tobacco leaves

Plant proteins have been attracting increasing attention due to their significant antiviral activity against tobacco mosaic virus (TMV). This paper aimed to investigate the tobacco endogenous protein and the anti-TMV effects. Firstly, the extraction of protein from discarded tobacco leaves (DTLP) was optimized by response surface methodology (RSM). The maximum DTLP yield reached to 8.32 % under the condition of solid-liquid ratio 1:19, temperature 60 degrees C and pH 12. DTLP was rich in hydrophilic amino acids, such as aspartic acid (8.08 +/- 0.34 g/ 100 g) and glutamic acid (8.02 +/- 0.42 g/100 g). DTLP structure was compact and stable with a denaturation temperature of 99.7 degrees C. Furthermore, the anti-TMV experiments revealed that DTLP showed inactive and protective activities against TMV with inhibitory rates (79.2 % and 75.4 %, respectively) at 500 mu g/mL, and inhibited the polymerization of TMV-CP to damage TMV particles. In addition, DTLP increased the expressions of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and phenylalanine ammonia lyase (PAL) in tobacco leaves by 1.55, 1.18, 9.13 and 2.92 times, respectively. Transcriptomics further verified that DTLP increased the expressions of TGA, WRKY, and PR1 genes for up-regulating the salicylic acid (SA) and pathogenesis-related proteins (PRs), thereby improving the system resistance of tobacco plants. Therefore, DTLP could be potentially developed as an alternative drug to treat plant viral diseases due to its broad-spectrum antiTMV activity.