JA-inducible expression of NtNAC56 regulates leaf senescence. A to C) RT-qPCR analysis of NtNAC56 (A), NtDOF2.1 (B), and NtRBCS (C) expression at different time points into MeJA treatment. Data are means ± Sd from three replicates. *P < 0.05 and **P < 0.01, Student's t-test. B) RT-qPCR validation of NtDOF2.1 expression after MeJA treatment at different time points. *P < 0.05 and **P < 0.01, Student's t-test. C) RT-qPCR validation of NtRBCS expression after MeJA treatment at different time points. *P < 0.05, Student's t-test. D) Histochemical analysis of β-GLUCURONIDASE (GUS) activity in NtNAC56 overexpression lines (NtNAC56-OE) tobacco plants harboring the NtNAC56pro:GUS reporter construct. Mock-treated NtNAC56-OE tobacco plants (left) and NtNAC56-OE tobacco plants treated with 100 μM MeJA (right) are shown. E) JA contents in WT and NtNAC56-OE leaves. Data are means ± Sd from three replicates. **P < 0.01, Student's t-test. F to J) RT-qPCR analysis of JA marker gene expression. Data are means ± Sd of three replicates. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001, Student's t-test.