ADENOSINE-DIPHOSPHATE GLUCOSE PYROPHOSPHORYLASE GENES IN WHEAT - DIFFERENTIAL EXPRESSION AND GENE-MAPPING

A full-length cDNA clone representing the large (shrunken-2) subunit o f ADP-glucose pyrophosphorylase (AGP; EC 2.7.7.27) has been isolated f rom a cDNA library prepared from developing grain of hexaploid wheat ( Triticum aestivum L., cv. Chinese Spring). The 2084-bp cDNA insert con tains an open reading frame of 1566 nucleotides and primer-extension a nalysis indicated that the 5' end is 10 nucleotides shorter than the m RNA. The deduced protein contains 522 amino acids (57.8 kDa) and inclu des a putative transit peptide of 62 amino acids (6.5 kDa). The simila rity of the deduced protein to the small subunit of AGP and to other A GP genes from plants and microorganisms is discussed. Northern hybridi sation shows that the Agp1 genes (encoding the small subunit in the wh eat endosperm) and the Agp2 genes (encoding the large subunit in the w heat endosperm) are differentially expressed in the wheat grain. Trans cripts from both gene sets accumulate to high levels in the endosperm during grain development with the majority of the expression in the en dopsperm rather than the embryo and pericarp layers. Although enzyme a ctivity is detected in developing grains prior to 10 d post anthesis, only the Agp1 genes are active at this time (the Agp2 genes are not ex pressed until 10 d post anthesis). The possibility that the enzyme exp ressed during early grain development is a homotetramer of small subun its is discussed. The Agp1 and Agp2 genes are arranged as triplicate s ets of single-copy homoeoloci in wheat. The Agp2 genes are located on the long arms of chromosomes 1A, 1B and 1D, about 80 cM from the centr omere. The Agp1 genes have been mapped to a position just distal to th e centromere on the long arms of chromosomes 7A, 7B and 7D.