Expression of 11s seed storage protein genes of Helianthus annuus L

Abstract

Many genes are expressed exclusively during plant embryo development. Among these, seed storage protein genes are of primary interest because they are expressed at very high levels only during specific periods of embryo maturation. Helianthinin is the major globulin storage protein of sunflower seeds. The physico-chemical characteristics and subunit composition of helianthinin resembles the 11S protein of pea seeds (legumin). Antiserum prepared against purified helianthinin was used to study storage protein accumulation in developing sunflower embryos. Synthesis of helianthinin begins within 7 days post fertilization (DPF) and it accumulates rapidly until 19 DPF. Storage protein synthesis then slows until seed maturation at 30 DPF. Anti-helianthinin was also used to select specific cDNA recombinants from a bacteriophage λgt11 cDNA expression library prepared from immature sunflower embryo polyadenylated RNA. One of these recombinants, λHa3, contained a 300 base pair (bp) cDNA insert which was used as a hybridization probe to select a recombinant containing a 1200 bp cDNA insert (λHa2). An additional helianthinin specific cDNA recombinant (λHa10) that is not homologous with Ha2 or Ha3 was selected from the library by differential screening. Ha2 and Ha3 cDNAs hybridize with an approximately 1.9 kilobase (kb) sunflower embryo transcript on RNA gel blots. Ha10 reacts with a slightly smaller transcript than Ha2 or Ha3. Helianthinin mRNA homologous to both Ha2/Ha3 and Ha10 is present in embryos 7 DPF and accumulates to maximum prevalence at 12 DPF which corresponds to the period of maximum helianthinin accumulation. Soon after 15 DPF, helianthinin RNA begins to decrease. Full length helianthinin mRNA is not detectable in mature seeds or in germinated seedlings. These results indicate that synthesis of the 11S sunflower seed storage protein occurs during a specific stage of embryogenesis and is regulated by the accumulation of helianthinin mRNA. Genomic DNA blot hybridizations indicate the presence of at least three helianthinin seed protein genes of the Ha2/Ha3 type and two of the Ha10 type in the sunflower genome...