| This proposal describes molecular and cellular studies on the wheat and rice prolamines, major proteins synthesized and accumulated during endosperm development. By screening two rice seed cDNA libraries, recombinant cDNA clones encoding the rice seed storage protein, prolamine, were isolated. Based on cross-hybridization and restriction enzyme map analysis, these clones can be divided into two homology classes. All clones contain a single open reading frame encoding a putative rice prolamine precursor (M.W. = 17,200) possessing a typical 14 amino acid signal peptide. The deduced primary structures of prolamine polypeptides are devoid of repetitive sequences, a feature prevalent in other cereal prolamines. Clones of the two homology classes share about 75% homology and diverged mainly by insertions/deletions of short nucleotide stretches and point mutations. An isolated genomic clone displays a highly conserved 2.5 kb EcoRI fragment, repeated in tandem 4 times, each containing the prolamine coding sequence. Close homology is exhibited by the coding segments of the genomic and cDNA sequences, although the 5;Developing wheat (Triticum aestivum L.) endosperm was examined using ultrathin sections prepared from tissues harvested at 5, 9, 16, and 25 days after flowering. Protein bodies are evident by 9 days and display a variety of membranous structures and inclusions. The Golgi apparatus is a prominent organelle at all stages, and by 9 days, are associated with small electron dense inclusions. By immunocytochemical techniques, glaidin (wheat prolamine) are localized within these vesicles and in homogeneous regions of protein bodies, but not in the lumen of the rough endoplasmic reticulum. The involvement of the Golgi apparatus in the packaging of gliadins into protein bodies indicates a pathway which differs from the mode of prolamine deposition in other cereals such as maize, rice and sorghum, and resembles the mechanism employed for the storage of rice glutelin and legume globulins. |
