Cloning and Characterization of ECPP44, a cDNA Encoding a 44- kilodalton Phosphoprotein Relating to Somatic Embryogenesis in Carrot.

Abstract

Somatic embryogenesis in Daucus carota can be induced by the treatment of shoot apices with various kinds of stress chemicals (Tachikawa et al., 1998). Using this system, we previously revealed the presence of a phosphoprotein (ECPP44) of which the phosphorylation was specific to embryogenic cells (EC), stress-treated shoot apices and somatic embryos, but not in non-embryogenic cells (NC). We then obtained a 141 by fragment of ECPP44 cDNA by RT-PCR with some primers based on the partial amino acid sequence. In this research, the fragment was used as a probe to screen the cDNA library which was compiled from somatic embryos. A full-length cDNA (925bp) corresponding to ECPP44 was isolated and sequenced. The putative amino acid sequence revealed that ECPP44 contained poly-serine consensus and nuclear targeting signal of Group II LEA genes. Phylogenetic analysis of the amino acid sequence encoded by ECPP44 showed that ECPP44 is a distant homology of the dehydrin family in carrot. ECPP44 is a single copy gene as evidenced by Southern blot analysis under high stringency. Northern blot analysis revealed that ECPP44 mRNA accumulates in EC, stress-treated and non-treated shoot apices, and somatic embryos, but not in NC. We discuss here the accumulation and/or phosphorylation of ECPP44 as it relates to the acquisition of embryogenic competence.