Abstract

GhNAC18 is a novel NAC gene that was isolated from cotton (Gossypium hirsutum L.). The full-length cDNA was 1511 bp including an open reading frame of 1260 bp in length and encodes a protein of 419 amino acids. With qRT-PCR analysis, GhNAC18 was downregulated during natural and dark-induced senescence, implicating this gene as anti-aging gene in cotton. Analysis of its promoter revealed a group of putative cis-acting elements especially, the light and stress responsive elements, indicating that it may have a potential role in leaf development. Additionally, GhNAC18 was found to have transcriptional activation activities on its C-terminal region and by bioinformatics analysis, GhNAC18 was localized in the nucleus. Tissue specific expression analysis indicated that GhNAC18 is constitutively expressed in roots, stems, earlier stages of senescing leaves, fibers and flower parts with high expression levels registered in the young leaves and cotyledon leaves. GhNAC18 was up-regulated by exogenous application of various phytohormones including salicylic acid (SA), methyl Jasmonate (MeJA) and ethylene (ET) but downregulated with abscisic acid (ABA).  Moreover, the gene was induced by drought (PEG6000), H₂O₂, cold (4°C) and wounding but was inhibited by high salinity. These results indicated that GhNAC18 is a transcriptional activator that is involved in leaf development, especially inhibition of leaf senescence and plant stress responses in cotton. This study provides fundamental information on understanding the function of GhNAC18 gene in cotton leaf senescence and stress tolerance and thereafter its manipulation for breeding of  late-aging and  stress-tolerant cultivars.

Key words: GhNAC18, stress response, senescence, Gossypium hirsutum L. NAC.

Abbreviation

SA, Salicylic acid; MeJA, methyl Jasmonate; ET, ethylene; ABA, abscisic acid; DNA, deoxyribonucleic acid; cDNA, complementary DNA; PCR, polymerase chain reaction; qRT-PCR, quantitative reverse transcription PCR; CTAB, cetyl trimethylammonium bromide; NJ, neighbor joining; ME, minimal evolution; MP, maximum parsimony; NS, non-senescent leaf; IS, initial senescent leaf; ES, early senescent leaf; LS, late senescent leaf; CS, complete senescent leaf; TFs, transcription factors; NAC, a family of transcription factors comprising NAM, ATAF1,2 and CUC; DREB, dehydration-responsive element-binding protein; ERF, ethylene-responsive factor; GhNAC18, NAC gene of Gossypium hirsutum L.