GUS-reporter based analysis of the promoter activity of Gossypium hirsutum NAC transcription factor, GhNAC4 that is induced by phytohormones and environmental stresses

Key message GhNAC4 gene is induced by phytohormones and environmental stress treatments in cotton. It is expressed throughout a mature plant, including the reproductive organs, vascular bundles, and guard cells. The expression analysis of GhNAC4, a NAC (NAM, ATAF1-2, and CUC2) domain-containing transcription factor of the upland cotton, Gossypium hirsutum was carried out. Its expression was up-regulated by abscisic acid, cytokinin, methyl jasmonic acid, gibberellic acid, auxin, and ethylene. Its expression was also highly induced by drought, osmotic, oxidative, salinity, high and low-temperature stresses, and wounding. To corroborate these observations, we cloned the promoter of GhNAC4 and fused it transcriptionally with uidA (GUS) gene for studies in transgenic tobacco. Fluorometric GUS analysis of the transgenic plants revealed that it is also induced by various phytohormones and environmental stresses. The spatio-temporal analysis of the GhNAC4 promoter revealed that GUS expression was active in all stages of plant development including the reproductive organs. In the mature plant, the GhNAC4 is expressed at a higher level in vascular bundles and guard cells. We also observed intense expression in other cells upon wounding. These observations were supported by a detailed bioinformatic analysis of the GhNAC4 promoter for identifying the cis-acting elements that are associated with the regulation of gene expression in a tissue-specific and induced manner.