Isolation and characterization of a cDNA that encodes ECP31, an embryogenic-cell protein from carrot

A full-length cDNA for ECP31, an embryogenic cell protein from carrot (Daucus carota L.) with a M(r) of 31,000 (Kiyosue T, Satoh S, Kamada H, Harada H (1991) Plant Physiol 95: 1077-1083), was isolated from a cDNA library prepared from embryogenic cells using PCR-amplified DNA as a probe. The genomic Southern blot analysis revealed that there are two or three genes for ECP31 in the carrot genome. The transcripts of ECP31 accumulated in the peripheral regions of clusters of embryogenic cells and disappeared in the course of somatic embryogenesis that was induced by transfer of the embryogenic cells to auxin-free media. The cDNA encodes a polypeptide of 256 amino acids, and the calculated molecular weight of this polypeptide is 26,111. The deduced amino acid sequence shows a high degree (62.2%) of similarity to that of a protein that is abundant during late embryogenesis of cotton (LEA D34; Baker JC, Steele C, Dure III (1988) Plant Mol Biol 11: 227-291). The mRNAs for ECP31 started to accumulate in zygotic embryos at a late stage of embryogenesis but were undetectable in mature embryos within 24 h after imbibition of seeds. In dry fruits (seeds), the transcripts were detected only in zygotic embryos by in situ hybridization. The level of ECP31 transcripts increased after treatment with abscisic acid (ABA) in torpedo-shaped somatic embryos but not in seven-day-old seedlings. These results suggest that both embryo-specific factor(s) and ABA are involved in the expression of the gene for ECP31.