Molecular Characterization of Six Tissue-Specific or Stress-Inducible Genes of NAC Transcription Factor Family in Tomato (Solanum lycopersicum)

NAC (NAM/ATAF1/2/CUC2) transcription factors comprise a large plant-specific gene family and play crucial roles in plant growth, development, and stress response. However, only little information regarding development- or stress-related NAC genes is available in tomato. In this study, six tomato NAC genes, designated as SlNAC5-SlNAC10, were characterized to encode NAC proteins that share high similarity with those known plant NACs, especially in the NAC domain. These SlNAC genes, except SlNAC10, have a conserved exon-intron structure despite their different intron length. Phylogenetic analysis suggested that SlNAC5, SlNAC7, and SlNAC10 may belong to the development-related NACs. Quantitative RT-PCR analysis revealed that the six SlNACs exhibited different tissue-specific (such as roots, leaves, and flowers) expression profiles, suggesting that they may have crucial and diverse roles during tomato growth and development. Varying degrees of induction were detected in the transcript level of these SlNACs except SlNAC6 when treated with multiple hormones including ABA, ACC, GA(3), MeJA, and IAA. The expression of SlNAC5-SlNAC10 was also checked under various abiotic stresses including NaCl, wounding, dehydration, and high/low temperature; six SlNACs were induced by these stresses with differential/similar induction levels. SlNAC5 was the most induced gene by NaCl stress with a 950-fold induction. Collectively, the results in this study of tissue-specific and/or stress-responsive SlNAC genes provide valuable information for further exploring the functional roles of NAC genes during tomato development and in response to environmental stresses, and one or more of them may hold promise for improving stress tolerance in transgenic tomato.