A promoter from the loblolly pine PtNIP1;1 gene directs expression in an early-embryogenesis and suspensor-specific fashion.

The PtNIP1;1 gene encodes an aquaglyceroporin that is expressed early in embryogenesis and appears to be expressed preferentially in the suspensor [V.T. Ciavatta et al. (2001) Plant Physiol 127:211-224]. An 899-bp fragment 5' to the PtNIP1;1 open reading frame (NIP(-899)) was cloned from loblolly pine (Pinus taeda L.) genomic DNA and fused to the beta-glucuronidase (GUS) reporter gene. The resulting plasmid, pNIP-GUS, was transformed into Norway spruce (Picea abies L.) embryogenic cultures by co-bombarding with a plasmid containing a bar gene construct as a selectable marker. The identity of lines selected on medium containing the herbicide Basta and showing beta-glucuronidase activity was confirmed by polymerase chain reaction as harboring GUS. Histochemical GUS assays of these lines revealed GUS activity in all cells of proembryogenic masses. During early embryogeny, GUS staining was intense in the suspensor region but not detectable in embryonal masses. GUS staining was absent by mid-embryogeny. By contrast, a control transgenic line, transformed with EuCAD-GUS, expressed GUS throughout embryo development. These results suggest that NIP(-899) contains elements that drive early embryogenesis-specific expression and suspensor-specific expression. This is the first example of a suspensor-specific promoter in conifers.