Temporal and spatial activities of a rice glutelin promoter in transgenic sorghum

Temporal and spatial patterns of expression of a uidA reporter gene, encoding the β-glucuronidase (GUS), driven by a rice glutelinA-2 (GluA-2) promoter, were evaluated in transgenic lines of sorghum. Quantitative GUS analysis conducted on seeds, harvested from T2 homozygous plants from three independent transgenic lines, showed detectable levels of expression of the transgene at 14 days post anthesis (dpa). From this point, GUS expression increased for about 1 week, but then declined during seed maturity. Furthermore, histochemical GUS analysis on seeds from the same transgenic lines revealed that the GluA-2 promoter directed GUS expression in the inner starchy endosperm portion of the seed. The absence of detectable GUS expression in the embryo, leaf, stem, root, pollen and inflorescence tissues suggests that this promoter is active specifically in the endosperm portion of the sorghum seed. Transcript analyses detected uidA mRNA in the seeds at 14 and 17 dpa, but not at other time points. Overall, these results suggest that the rice GluA-2 promoter is an endosperm-specific promoter in sorghum and that it can serve as a valuable tool in improving the seed quality of this cereal.