Transient expression of the uidA gene in pollen embryoids of wheat following microprojectile bombardment

Abstract

Transient GUS expression levels in microprojectile bombarded, microspore-derived embryoids of bread wheat ( Triticum aestivum cv. Pavon) were evaluated when varying the stage of embryoid development, time in culture, type of promoter, and other physical parameters. GUS expression was histochemically measured 48 h after delivery of the uidA gene. The maize ubiquitin 1 promoter provided a higher level of GUS expression than the CaMV 35S or pollen-specific Zm13 promoters. The stage of embryogenic development had little effect on transient expression up to 10 weeks in culture, after which efficiency dropped off dramatically. The source of calcium used to precipitate the DNA onto microcarriers had a profound influence and GUS expression was enhanced significantly when the calcium solution was at pH 10. Bombardment did not inhibit regeneration and GUS expression could be detected in embryoids producing roots, stems, and leaves 21 days after transformation. These results show that this system is useful for transient expression assays and suggests that the stable transformation of wheat using microspore-derived embryoids may be a practical alternative to methods involving prolonged tissue culture and regeneration from undifferentiated callus cultures.