Transient overexpression of CaNAC2cpromoted thermotolerance and hypersensitivity reaction (HR) mimic cell death and expression of defense related genes
To confirm the result from VIGS, we assayed the effect of CaNAC2ctransient overexpression(CaNAC2c -TO) on Fv/Fm and △F/Fm’ and expression of thermotolerance related genes, the result showed thatCaNAC2c was successfully expressed in pepper leaves (Figure 3A), and Fv/Fm and △F/Fm’ in pepper leaves were significantly promoted byCaNAC2c -TOunder HTS (Figure 3B and C), coupled with enhanced expression of thermotolerance related genes including CaHSFB2A ,CaHSP2 4 and CaHSP70 (Figure 3D).
Since resistance to RSI and thermotolerance are two different processes, we study the switching of CaNAC2c function in different treatments. In parallel, CaNAC2c -TOwas found to trigger clear HR mimic cell death at room temperature, increased accumulation H2O2 displayed with darker DAB staining upon challenge of RSI, while the exogenous applied ABA blocked the cell death. By contrast, at 37℃, CaNAC2c -TO did not trigger any cell death, but the exogenous application of fluridon, an inhibitor of biosynthesis of ABA, restored the cell death triggered byCaNAC2c -TO at 37℃ (Figure 3E and F), indicating that ABA might confer the repression of cell death induction of CaNAC2c at 37℃. In addition, it was found that both SA signaling dependent CaNPR1and JA signaling dependent CaDEF1 were depressed by HTS (Figure 3G), although CaNPR1 was depressed, CaDEF1 and HR relatedCaHIR1 was induced by CaNAC2c -TO at room temperature (Figure 3G), indicating that CaNAC2c acts as positive regulator in JA-dependent immunity and HR but a negative regulator in SA-dependent immunity. These results suggest that CaNAC2c might have different transcriptional regulation directions under RSI and HTS.