Abundance, diversity, and regulation of mRNA sequence sets in soybean embryogenesis

Soybean embryo mRNA populations were compared with respect to complexity, abundance distribution, and sequence representation. RNA-excess hybridization experiments with cDNA and single-copy DNA showed that cotyledon-stage (30 days after flowering (DAF)) and mid-maturation-stage (75 DAF) embryos contained similar numbers of diverse mRNAs (14,000–18,000) but that their mRNA frequency distributions were vastly different. Hybridization experiments with kinetically selected mid-maturation-stage abundant and rare cDNAs demonstrated that the diverse mRNAs of cotyledon-stage and mid-maturation-stage embryos were similar, and that most embryonic mRNAs persist throughout development and are stored in the dormant seed. We have, however, identified a small number (7–10) of superabundant mRNAs which collectively comprise about 50% of the mid-maturation-stage mRNA mass. These mRNAs are quantitatively modulated in development, are embryo specific, and are encoded by low-frequency repetitive DNA sequences. This developmentally regulated mRNA set probably codes for a spectrum of seed proteins which accumulate during maturation.