Molecular characterization of PgAGO, a novel conifer gene of the ARGONAUTE family expressed in apical cells and required for somatic embryo development in spruce

• Published in: Tree physiology Vol. 26; no. 10; pp. 1257 - 1270
• Main Authors: Tahir, M, Law, D.A, Stasolla, C
• Format: Journal Article
• Language: English
• Published: Canada 01.10.2006
• Subjects: Amino Acid Sequence; amino acid sequences; apical meristems; Cell Line, Transformed; Cotyledon - cytology; Cotyledon - genetics; developmental stages; forest trees; gene expression; Gene Expression Regulation, Developmental; Gene Expression Regulation, Plant; genes; genetic code; Germination - physiology; In Situ Hybridization; Meristem - cytology; Meristem - genetics; Molecular Sequence Data; nucleotide sequences; Phylogeny; Picea - genetics; Picea - metabolism; Picea glauca; plant anatomy; Plant Proteins - genetics; Plant Proteins - metabolism; protein composition; protein synthesis; Reverse Transcriptase Polymerase Chain Reaction; RNA; RNA, Messenger - metabolism; Sequence Alignment; Sequence Homology, Amino Acid; somatic embryogenesis; somatic embryos; transcription (genetics); Trees - genetics; Trees - metabolism
• ISSN: 0829-318X; 1758-4469
• DOI: 10.1093/treephys/26.10.1257

A new member of the Argonaute (AGO) family of proteins was isolated from conifers and designated as PgAGO (Gene Bank Accession No. DQ068741; protein ID AAY67884). The complete coding sequence of PgAGO was obtained through screening cDNA libraries generated from white spruce (Picea glauca (Moench) Voss) somatic embryos. The PgAGO gene has an open reading frame of 2880 bp and encodes a protein of 960 amino acids. The predicted protein has an isolectric point of 9.17, a molecular mass of 107 kD and lacks prominent hydrophobic domains, which makes its cellular location inconclusive. The PgAGO protein contains the two conserved regions (the PAZ and PIWI domains) typically found in all members of the AGO family. The PAZ domain of PgAGO comprises 117 amino acid residues and shares a low degree of homology with similar domains in other species. The C-terminal PIWI domain contains 86 amino acids and is more conserved. Localization and transformation studies suggest that PgAGO is required for embryo development, specifically for proper shoot and root apical meristem differentiation. Based on RNA-in situ hybridization, the PgAGO transcripts are preferentially localized in cells of the shoot and root apical meristems from the early phases of embryo development. The RNA-mediated suppression of PgAGO results in severe abnormalities during embryo development, including the formation of poorly organized apical meristems. The root meristems lack the group of large central cells that separate the procambial region from the root cap, whereas the shoot meristem fails to differentiate apical initials. These abnormalities result in poor post-embryonic performance, leading to meristem abortion and growth cessation.