The multiple stress-responsive transcription factor SlNAC1 improves the chilling tolerance of tomato

NAC (NAM-ATAF1, 2-CUC2) family members play important roles in various environmental responses. Here, we cloned a full-length NAC gene (954bp) from Solanum lycopersicum (SlNAC1). This gene belonged to ATAF subfamily which included ATAF1 and ATAF2 of Arabidopsis thaliana. SlNAC1 expression was induced by chilling stress (4 degrees C), heat stress (40 degrees C), high salinity, osmotic stress and mechanical wounding. SlNAC1 transcripts were enhanced after application of abscisic acid, methyl jasmonate, salicylic acid, gibberellin, ethylene, methyl viologen and hydrogen peroxide. The seedlings of transgenic plants overexpressing SlNAC1 grew more leaves but were shorter than wild-type (WT) plants. SlNAC1 overexpression increased the chilling tolerance of tomato plants by maintaining the higher maximal photochemical efficiency of photosystem II and oxygen-evolving activities. Compared with WT plants, transgenic plants showed higher superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) activities, which reduced levels of H2O2 and superoxide anion radicals and promoted lower ion leakage and malondialdehyde content. The expression level of SlCBF1 in transgenic plants was also higher than that in WT plants under both normal conditions and chilling stress; this increased expression may be the main factor influencing the high chilling tolerance of transgenic plants. The results suggest that SlNAC1 plays important roles in diversiform plant-stress responses and diverse signaling pathways.