Abstract: 【Objective】The primary objectives of this experiment are to clone GhNAC7 gene, analyze its structure, detect its expression in different tissues of cotton and at different developmental leaf senescence stages. Furthermore, its function in cotton leaf senescence was further studied through transforming GhNAC7 gene into Arabidopsis. 【Method】Based on the cotton senescent leaves cDNA library, which was built by state key laboratory of cotton biology of institute of cotton research of CAAS, this gene was cloned from upland cotton using an expressed sequence tag (EST) containing NAM domain after designing primer using Oligo 6.71. Gene Structure Display Sever was conducted to analyze its structure, PlantCARE was used on-line to study its promoter sequence, and GenScan was simultaneously performed to translate amino acid on-line. Meanwhile, NAC family genes with higher scores were chosen after aligning sequence from Arabidopsis in TAIR. Afterwards MEGA 6.06 was used to display evolutionary relationships of the gene and GeneDOC was conducted to perform sequence alignment of amino acids. Via constructing 35S::GhNAC7-GFP fusion expression vector with XbaⅠand SacⅠrestriction sites, subcellular localization of GhNAC7 was studied by transient expression analysis of onion epidermal cells. Expression profiles of GhNAC7 in various tissues, in response to 200 μmol·L^-1 ABA treatment and developmental leaf senescence stages were investigated through quantitative real-time PCR (qRT-PCR). Its promoter specificity was conducted by transforming into Arabidopsis thaliana after constructing pGhNAC7-GUS fusion expression vector. Simultaneously, using pBI101 and pBI121 with EcoRⅠand SalⅠrestriction sites were used to construct fusion expression vectors, and then over-expression analysis was performed by transforming GhNAC7 into Arabidopsis thaliana.【Result】 In this study, a novel gene GhNAC7 was successfully cloned from upland cotton (Gossypium hirsutum L.). Its full-length was 1 064 bp with three exons and two introns. Results of bioinformatics analysis exhibited that its open reading frame (ORF) was 834 bp, which encoding 277 amino acids. The molecular weights of GhNAC7 encoding protein were 31.35 kD and isoelectric point was 9.22. Domain analysis of GhNAC7 showed that it belongs to the NAM subgroup of NAC family, moreover phylogenetic tree analysis showed that GhNAC7 has the closest genetic relationship with ANAC041 and ANAC083, and GhNAC7 displayed the same domain positions with ANAC083 at 17-58 aa. Its core promoter elements were also predicted, which contained a series of aging, hormone, stress-related cis-acting elements. Subcellular localization elucidated the protein of GhNAC7 encoding is a nucleoprotein. Tissue-specific analysis showed that this gene was significantly expressed in true leaves, cotyledons, flowers, anthers and senescent leaves, but displayed the highest expression in senescent leaves. And in promoter specificity analysis, it was also exhibited the strongest GUS activity in senescent leaf. Over-expression in transgenic Arabidopsis verified evident symptoms of aging compared to the wild type. Fluorescence quantitative PCR analysis showed that the gene expression was significantly up-regulated after 6 h of ABA treatment and displayed the highest at 48 h, so it was hypothesized that ABA could regulate GhNAC7 gene expression to mediate cotton leaf senescence.【Conclusion】It was concluded that GhNAC7 gene could promote cotton leaf senescence and be regulated by ABA.

Key words: upland cotton, NAM domain, leaf senescence, GhNAC7, over-expression