Abstract:

【Objective】 NAC transcription factors play an important role in regulating plant growth, development and response to stress tolerance. Studying the sequence, structure, evolutionary relationship and expression pattern of NAC transcription factor gene family related with stress tolerance in willow will have important theoretical significance for understanding the molecular mechanism underlying stress tolerance, which in turn will provide a theoretical basis for molecular assisted breeding in future.【Method】 Two members of the NAC gene family were cloned based on the RNA-seq data of the Salix × jiangsuensis ‘J2345’ variety. The gene structure, protein properties and gene phylogeny were analyzed by using bioinformatics. The tissue specific expression in leaf and root, as well as the expression patterns under different types of stress was detected by quantitative real time PCR. 【Result】 The two NAC transcription factors cloned from the leaves of Salix × jiangsuensis ‘J2345’ variety were named SlNAC1 and SlNAC2. Bioinformatics analysis results showed that the sequence lengths of SlNAC1 and SlNAC2 were 1 126 bp and 1 139 bp, encoding proteins with 343 and 291 amino acid residues, respectively. The molecular weight of the proteins expressed from the two SlNAC1 and SlNAC2 genes were 40.1 ku and 42.3 ku, respectively, and both were stable, hydrophilic proteins. The SlNAC1 gene was located in nucleus while the SlNAC2 gene was located in chloroplast. Sequence alignment showed that both the genes contained typical NAM domains as well as A, B, C, D and E sub-domains, which shared the LPPG, YPNG and DEE conservative motifs and NAC suppression domains. Phylogenetic analysis demonstrated that SlNAC1 and SlNAC2 shared the highest homology with the genes from Manihot esculenta and Solanum melongena, respectively. RT-PCR results showed that both SlNAC1 and SlNAC2 were expressed in leaves and not in roots. The results of qRT-PCR showed that SlNAC1 was significantly upregulated after 24 hours of abscisic acid (ABA) and gibberellins (GA) treatments. SlNAC2 was significantly upregulated after exposure to polyethylene glycol (PEG), ABA and GA stresses. 【Conclusion】 The transcription factor SlNAC1 can be induced by induced by ABA and GA, and could stably express under abiotic stress. SlNAC2 can be induced by PEG, ABA and GA rather than ethrel (ETH), at a significantly higher expression level than SlNAC1. Therefore, we speculated that SlNAC1 and SlNAC2 were involved in GA and ABA signal transduction, but not in th e ETH signaling pathway.

Key words: Salix, NAC gene family, gene cloning, gene expression