Patterns of Expression of the Genes for Glutamine Synthetase Isoforms during Somatic and Zygotic Embryogenesis in Carrot

Abstract

Three cDNA clones encoding isoforms of carrot glutamine synthetase (GS) were isolated and used as probes for analysis of the patterns of expression of the genes for GS isoforms during somatic embryogenesis and seed development in carrot. Transcripts corresponding to two of the cDNAs, CGS102 and CGS201, accumulated in both somatic embryos and developing seeds in the same manner. Their levels were high at the early stage of embryogenesis but decreased at the late stage. This pattern of expression is similar to the pattern of changes in GS activity observed during somatic embryogenesis. In contrast, expression of the transcript for another GS isoform detected with CGS103 cDNA was observed at the late stage of seed development and in senesced leaves but not in somatic embryos or young leaves. We also analyzed the levels of the transcripts in somatic embryos that had been cultured in media with either ammonium ions or glutamine as the nitrogen source. The amounts of the CGS102 and CGS201 transcripts fell when glutamine was supplied in the medium. These results indicated that GS activity was regulated at the transcriptional level and that the pattern of expression of the genes for GS during somatic embryogenesis reflected that during zygotic embryogenesis. It is possible that somatic embryogenesis and zygotic embryogenesis have common regulatory systems with respect to nitrogen metabolism.

Characterization and expression pattern analysis of DcNAC gene in somatic embryos of Dendrobium candidum Wall Ex Lindl.

“…Thus, the whole process of embryo development in orchids, especially the mechanism regulating embryogenesis, is poorly understood. Somatic embryogenesis shares considerable similarity with zygotic embryogenesis (Zimmerman 1993;Higashi et al 1998), probably due to the conservation of the underlying cellular and molecular mechanisms between two, thus providing an attractive model system for studying orchid embryogenesis, including cytological features and molecular regulation mechanisms.…”

Differential proteomic analysis of developmental stages of Acca sellowiana somatic embryos

“…In higher plants, GS is an octameric enzyme 310-350 kD that occurs as a number of isoenzymes, located both in the plastids (GS2) and in the cytosol (GS1) (Li et al 1993). Higashi et al (1998) investigated the expression pattern of three carrot cDNA clone codings for three isoforms of the enzyme glutamine synthetase during somatic as well as zygotic embryogenesis. Transcription levels of CGS102 and CGS201 increased during the early stages of somatic embryogenesis and developing seeds, whereas CGS103 was expressed only in the later stages of seed development and in senescent leaves, being absent in somatic embryos and young leaves.…”

Progress in understanding the regulation and expression of genes during plant somatic embryogenesis: A review

“…In further study, expression pattern of three carrot cDNA clones coding for the three isoforms of the enzyme glutamine synthetase (GS) (CGS102, CGS103, and CGS201) was investigated during somatic as well as zygotic embryogenesis [57].…”

“…In addition, the expression of CGS102 and CGS201 was found to decline in the presence of medium supplemented with glutamine as nitrogen source, indicating transcriptional regulation of GS activity. This also signifies the involvement of a common regulatory system for nitrogen metabolism in somatic and zygotic embryogenesis [9,15,57].…”