THE PROMOTER OF THE BARLEY ALEURONE-SPECIFIC GENE ENCODING A PUTATIVE7-KDA LIPID TRANSFER PROTEIN CONFERS ALEURONE CELL-SPECIFIC EXPRESSION IN TRANSGENIC RICE

This paper describes the aleurone-specific gene Ltp2 from barley, whic h encodes a putative 7 kDa nonspecific lipid transfer protein. As show n by Northern and in situ hybridization analyses, the Ltp2 transcript is present in barley aleurone cells shortly after the initiation of al eurone cell differentiation. The expression of Ltp2 increases until gr ain mid-maturity, but the mRNA is absent from mature grains. The Ltp2 transcript is undetectable in the embryo and vegetative tissues, confi rming the aleurone specificity of the Ltp2 gene. The ability of the is olated 801 bp Ltp2 promoter to direct aleurone-specific expression in immature barley grains is demonstrated by particle bombardment experim ents. In these experiments, the activity of the Ltp2 promoter is 5% of the activity of the strong constitutive Actin1 promoter from rice, as quantified by GUS activity measurements. In stably transformed rice p lants containing the Ltp2 promoter-Gus construct, the specificity of t he Ltp2 promoter is confirmed in vivo by the presence of GUS activity exclusively in the aleurone layer. This study demonstrates the conserv ed nature of the regulatory signals involved in aleurone-specific gene transcription in cereal grains.