Expression of storage protein genes in oat seeds
Abstract
Developing seeds synthesize storage protein reserves that will be catabolized during germination to provide nutrients for the young seedling. Oat seeds synthesize two major storage protein types: 50-80% of the seed protein is saline-soluble globulin and 10-20% is alcohol-soluble prolamines, called avenins. The structure of the oat globulins is known to be similar to that of the globulins that predominate in many dicot species, but the avenins have not been extensively characterized. The sequences of three avenin cDNA clones are reported in this thesis. Major features of the encoded proteins include a 19-amino acid signal sequence, two sets of glutamine-rich tandem repeats separated by a 63-amino acid conserved region, and a short polyglutamine tract. The avenin clones have nucleotide sequence homology to prolamines from wheat, rye, and barley. Hybridization analysis of genomic DNA shows that avenins are encoded by approximately 25 genes and globulins by at least 50 genes per haploid genome in Avena sativa. Similar ratios of avenin to globulin sequences were seen in other Avena species, but it is not known how many of these sequences are functional genes. Expression of the genes that encode avenins and globulins was studied. The mRNAs encoding both protein classes are present in significant quantities by 4 days after anthesis (DAA), and the levels of both peak at 8 DAA. There are more avenin mRNAs than globulin mRNAs throughout most of seed development. Protein accumulation begins between 4 and 6 DAA for both avenin and globulin. The intracellular pathway of synthesis and deposition of oat storage proteins was studied by electron microscopy using colloidal-gold immunolocalization. It was found that avenin and globulin are stored in the same vacuolar protein bodies, but that avenins are deposited in light-staining spherical inclusions within a dark-staining matrix that contains the globulins. This arrangement is different from that observed in the seeds of any cereal species studied to date.
Degree
Ph.D.
Advisors
Larkins, Purdue University.
Subject Area
Botany|Genetics
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