Spatial and temporal regulation of a soybean (Glycine max) lectin promoter in transgenic cotton (Gossypium hirsutum)

The activity of a soybean (Glycine max L. Merrill) lectin gene promoter was investigated in transgenic cotton plants (Gossypium hirsutum L.) with the view to using this promoter for the seed-specific alteration of gossypol, a secondary metabolite in cotton that has adverse effects on the nutritional value of cottonseed products like oil and protein-rich meal. Agrobacterium-mediated transformation generated stable transformants containing a construct with the lectin promoter fused to the β-glucuronidase reporter gene (pLeGUS). Fluorometric GUS assays and northern hybridization detected strong promoter activity during embryo development. GUS activity in developing embryos was detected as early as 10 d post-anthesis (dpa), peaking late in embryo maturation. Enzyme activity persisted in imbibed mature seed, and negligible activity remained detectable in the roots and cotyledons of 7-d-old seedlings. No GUS activity was detected in leaves and squares of mature plants. GUS transcripts increased during embryo development to peak about 35 dpa, declining to a low level in imbibed mature seed. No transcripts were detected in roots, cotyledons, leaves or squares. Histochemical GUS activity staining indicated promoter activity in all cells of the cotyledons, including the flattened cells of the gossypol glands, the presumed site of synthesis of gossypol. This study concluded that the soybean lectin gene promoter is a useful tool for the seed-specific expression of transgenes in cotton.