The functionality of α-kafirin promoter and α-kafirin signal peptide

Cereal grains offer great potential as a storage system for production of highly valuable proteins using biotechnological approaches, but such applications require tight temporal and spatial control of transgene expression. Towards this aim, we have undertaken a detailed analysis of α - kafirin ( α - kaf) promoter and α - kaf signal peptide ( sp ) in transgenic sorghum plants, using green fluorescent protein gene ( gfp ) as a reporter. Constructs containing either the α - kaf promoter or the constitutive maize ubiquitin-1 ( ubi ) promoter driving either gfp or sp-gfp translational fusion were introduced into Sorghum bicolor inbred line Tx430 by particle bombardment. We show for the first time that the α - kaf promoter directs endosperm-specific transgene expression, with activity first detected at 10 days post-anthesis (dpa), peaking at 20 dpa, and remaining active through to physiological maturity. Furthermore, we demonstrate for the first time that the α -kafirin sp is sufficient to direct foreign protein to protein bodies in the endosperm. The evidence is also provided for possible mis-targeting by α - kaf sp in vegetative tissues of transgenic lines with ubi - sp - gfp , resulting in loss of reporter gene translational activity that no GFP signal was observed. These results demonstrate that α - kaf promoter and α - kaf sp are well suited for seed bioengineering to produce recombinant proteins in sorghum endosperm or deposit foreign proteins into sorghum protein bodies.