Developmentally regulated expression of a sunflower 11S seed protein gene in transgenic tobacco.
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abstract
Helianthinin is the major 11S seed storage protein of sunflower (Helianthus annuus). Like most seed proteins, helianthinin is encoded by a small gene family; two members of this gene family, HaG3-A and HaG3-D, have been isolated and characterized. Tobacco was transformed with a 6 kb fragment of HaG3-A containing the helianthinin coding region flanked by 3.8 kb upstream and 0.4 kb downstream sequence. Expression of helianthinin was developmentally regulated in seeds of transgenic tobacco plants; furthermore, helianthinin polypeptides were proteolytically processed and targeted to the protein bodies of transgenic tobacco. A fragment of HaG3-A from -2376 to +24 was fused to the beta-glucuronidase (GUS) reporter gene and transferred to tobacco. GUS expression driven by this helianthinin upstream region was developmentally regulated in seeds. Germinating seedlings of the same transformant exhibited a time-dependent decrease in GUS activity with none detected by 6 days post imbibition (DPI). Histochemical analysis of GUS activity in embryos and 2 to 5 DPI seedlings showed expression restricted to the cotyledons and upper embryonic axis with none detected at the radicle end. No GUS activity was found in cotyledons, hypocotyls, leaves, and roots of 18 day seedlings or in leaves of an 8 week F1 plant. These results indicate that the cis-regulatory elements required for developmental control of the HaG3-A helianthinin gene are located in a 2.4 kb upstream region of this gene. This region was sequenced together with the upstream region of the HaG3-D helianthinin gene.
