Somatic Embryogenesis Receptor-like Kinase Research Articles

EST Sequencing from Embryogenic Cyclamen persicum Cell Cultures Identifies a High Proportion of Transcripts Homologous to Plant Genes Involved in Somatic Embryogenesis

To learn more about the process of somatic embryogenesis in the economically important ornamental plant Cyclamen persicum, we initiated an expressed sequence tag (EST) project. A normalized cDNA library was constructed from embryogenic cell material in different developmental stages, and clones were subsequently sequenced from the 5′ end. A total of 2083 filtered EST with an average length of 499 bases were analyzed in this study and submitted to the international sequence databases. By computational analyses, the Cyclamen transcripts were annotated and checked against plant genes previously described to be involved in somatic embryogenesis. Approximately one third of those genes were covered by the Cyclamen EST analyzed in this study. A high proportion of homologs to genes involved in somatic embryogenesis in the model system Daucus carota (carrot) were found in the Cyclamen EST collection. Of special interest are transcripts encoding gibberellin oxidases and somatic embryogenesis receptor-like kinases (SERK), both of which were confirmed to be important for development of embryos from somatic carrot cells. In addition, the set of candidate genes was expanded by using gene ontology (GO) annotations as well as by comparison with EST that were shown to be upregulated during Glycine max (soybean) somatic embryogenesis in a microarray approach. Our computational biology approach disclosed a set of around 90 candidate genes that now can be tested in the wet lab for their influence on somatic embryogenesis in Cyclamen. The annotated Cyclamen transcripts are available via http://www.Cyclamen-est.de.

The Arabidopsis SERK1 protein interacts with the AAA-ATPase AtCDC48, the 14-3-3 protein GF14λ and the PP2C phosphatase KAPP

Leucine-rich repeat (LRR)-containing transmembrane receptor-like kinases (RLKs) are important components of plant signal transduction. The Arabidopsis thaliana somatic embryogenesis receptor-like kinase 1 (AtSERK1) is an LRR-RLK proposed to participate in a signal transduction cascade involved in embryo development. By yeast two-hybrid screening we identified AtCDC48, a homologue of the mammalian AAA-ATPase p97 and GF14lambda, a member of the Arabidopsis family of 14-3-3 proteins as AtSERK1 interactors. In vitro, the AtSERK1 kinase domain is able to transphosphorylate and bind both AtCDC48 and GF14lambda. In yeast, AtCDC48 interacts with GF14lambda and with the PP2C phosphatase KAPP. In plant protoplasts AtSERK1 interacts with GF14lambda.

Characterisation of the cacao somatic embryogenesis receptor-like kinase ( SERK) gene expressed during somatic embryogenesis

Somatic embryogenesis is a useful tool for plant propagation and consists of a good model for embryo development studies. During somatic embryogenesis, some morphological and biochemical changes occur in response to alterations in gene expression patterns. The somatic embryogenesis receptor kinase ( SERK) gene is an important element related to this process. In this work we have focused on the function of SERK in Theobroma cacao. Our main questions were whether this gene exists in this plant with another arrangement; if it is functional and, in a positive case, in which tissues it acts. We have found only one copy of SERK that is functional and analyzed its expression in a series of tissues. The phylogenetic tree showed that the available sequences of SERK are highly conserved and a considerable number of species contain different sequences of SERK, confirming it as a gene family with variant repeats.

Isolation and characterization of the somatic embryogenesis receptor-like kinase gene homologue (CitSERK1) from Citrus unshiu Marc.

A cDNA clone was isolated for a somatic embryogenesis receptor-like kinase (SERK) gene homologue (CitSERK1) from Citrus unshiu Marc. CitSERK1 revealed high amino acid sequence homologies to the past isolated SERK genes of Arabidopsis thaliana, Zea mays, and Daucus carota and had the common structural features of a putative leucine zipper (ZIP) with five repeat units in the extracellular domain, a proline-rich region (SPP) just upstream of the transmembrane domain, and the kinase domain in the C-terminal. The mRNA expression of CitSERK1 was relatively uniform in all plant tissues except those of mature fruit at days after flowering (DAF) 180 and abundant around the stage of nucleous division and enlargement. During callus culture, the transcripts of CitSERK1 were less than the detectable levels in proliferating non-embryogenic calli but increased until they could be detected in the calli after the initiation of embryogenesis, suggesting that CitSERK1 could be involved in embryogenesis or embryo development. In addition, genetic linkage analysis showed that the SERK1 locus was independent of both loci concerning two traits, polyembryony and seedlessness derived from Satsuma mandarin, which have been considered to be highly important characteristics in Citrus genetic improvement.

Spatial expression of a sunflower SERK gene during induction of somatic embryogenesis and shoot organogenesis

Organogenesis or somatic embryogenesis can be induced on immature zygotic embryos (IZE) of sunflower depending on the culture conditions. Both morphogenic processes originate from the same group of cells and show identical kinetics. Using real-time PCR and in situ hybridisation, we showed that somatic embryogenesis receptor-like kinase ( SERK) transcripts accumulate early after the beginning of the culture in the morphogenic zone of IZE explants whatever the induction conditions used, i.e. organogenic, embryogenic or highly embryogenic conditions. Quantitative analyses failed to show any correlation between the SERK expression level during the period decisive for the orientation of the morphogenic pathway, i.e. the first 2 days of culture, and the type of morphogenesis induced. However, after 2 days of culture on the organogenic medium, the SERK gene expression level was severely down-regulated in the IZE explants. At 4 days of culture, SERK transcripts were no longer detectable by in situ hybridisation in the developing shoot structures whereas they still continued to accumulate in the embryonic structures induced on both embryogenic and highly embryogenic culture media. The significance of these expression analyses was addressed by transfer medium experiments. Results revealed that IZE cultured on the organogenic medium were able to form somatic embryos when transferred on the highly embryogenic medium as long as the SERK transcripts accumulated at a high level in their morphogenic zone, i.e. first 2 days of culture. Passt this delay, explants rapidly lost their embryogenic competence. Indeed, after 4 days of culture on the organogenic medium, IZE were definitely oriented towards shoot organogenesis. Taken together, these data suggest that reactive cells of IZE develop the competence to somatic embryogenesis during the first day of culture whatever the morphogenic induction conditions used.

The ArabidopsisSomatic Embryogenesis Receptor Kinase 1Gene Is Expressed in Developing Ovules and Embryos and Enhances Embryogenic Competence in Culture

AbstractWe report here the isolation of the Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1 (AtSERK1) gene and we demonstrate its role during establishment of somatic embryogenesis in culture. The AtSERK1 gene is highly expressed during embryogenic cell formation in culture and during early embryogenesis. The AtSERK1 gene is first expressed in planta during megasporogenesis in the nucleus of developing ovules, in the functional megaspore, and in all cells of the embryo sac up to fertilization. After fertilization, AtSERK1 expression is seen in all cells of the developing embryo until the heart stage. After this stage, AtSERK1 expression is no longer detectable in the embryo or in any part of the developing seed. Low expression is detected in adult vascular tissue. Ectopic expression of the full-length AtSERK1 cDNA under the control of the cauliflower mosaic virus 35S promoter did not result in any altered plant phenotype. However, seedlings that overexpressed theAtSERK1 mRNA exhibited a 3- to 4-fold increase in efficiency for initiation of somatic embryogenesis. Thus, an increased AtSERK1 level is sufficient to confer embryogenic competence in culture.

The Arabidopsis Somatic Embryogenesis Receptor Kinase 1 Gene Is Expressed in Developing Ovules and Embryos and Enhances Embryogenic Competence in Culture

We report here the isolation of the Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1 (AtSERK1) gene and we demonstrate its role during establishment of somatic embryogenesis in culture. The AtSERK1 gene is highly expressed during embryogenic cell formation in culture and during early embryogenesis. The AtSERK1 gene is first expressed in planta during megasporogenesis in the nucellus [corrected] of developing ovules, in the functional megaspore, and in all cells of the embryo sac up to fertilization. After fertilization, AtSERK1 expression is seen in all cells of the developing embryo until the heart stage. After this stage, AtSERK1 expression is no longer detectable in the embryo or in any part of the developing seed. Low expression is detected in adult vascular tissue. Ectopic expression of the full-length AtSERK1 cDNA under the control of the cauliflower mosaic virus 35S promoter did not result in any altered plant phenotype. However, seedlings that overexpressed the AtSERK1 mRNA exhibited a 3- to 4-fold increase in efficiency for initiation of somatic embryogenesis. Thus, an increased AtSERK1 level is sufficient to confer embryogenic competence in culture.

Molecular characterisation of two novel maize LRR receptor-like kinases, which belong to the SERK gene family.

Genes encoding two novel members of the leucine-rich repeat receptor-like kinase (LRR-RLK) superfamily have been isolated from maize (Zea mays L.). These genes have been named ZmSERK1 and ZmSERK2 since features such as a putative leucine zipper (ZIP) and five leucine rich repeats in the extracellular domain, a proline-rich region (SPP) just upstream of the transmembrane domain and a C-terminal extension (C) after the kinase domain identify them as members of the SERK (somatic embryogenesis receptor-like kinase) family. ZmSERK1 and ZmSERK2 are single-copy genes and show 79% identity among each other in their nucleotide sequences. They share a conserved intron/exon structure with other members of the SERK family. In the maize genome, ZmSERK1 maps to position 76.9 on chromosome arm 10L and ZmSERK2 to position 143.5 on chromosome arm 5L, in regions generally not involved in duplications. ZmSERK1 is preferentially expressed in male and female reproductive tissues with strongest expression in microspores. In contrast, ZmSERK2 expression is relatively uniform in all tissues investigated. Both genes are expressed in embryogenic and non-embryogenic callus cultures.

Embryogenic cells in Dactylis glomerata L. (Poaceae) explants identified by cell tracking and by SERK expression.

Single mesophyll cells in leaf explants of Dactylis glomerata L. (Dactylis) that were competent to form somatic embryos directly or through callus were identified by semi-automatic cell tracking. These competent cells were a subpopulation of small, isodiametric, cytoplasm-rich cells located close to the vascular bundles. Using whole mount in situ hybridization, we showed that a similar subpopulation of cells expressed the Somatic Embryogenesis Receptor-like Kinase (SERK) gene during the induction of embryogenic cell formation. In both leaf explants and suspension cultures, a transient pattern of SERK gene expression was found during early embryo development, up to the globular stage. In later embryo stages, SERK mRNA was present in the shoot apical meristem, scutellum, coleoptile and coleorhiza.

A leucine-rich repeat containing receptor-like kinase marks somatic plant cells competent to form embryos.

The first somatic single cells of carrot hypocotyl explants having the competence to form embryos in the presence of 2,4-dichlorophenoxyacetic acid (2,4-D) were identified using semi-automatic cell tracking. These competent cells are present as a small subpopulation of enlarged and vacuolated cells derived from cytoplasm-rich and rapidly proliferating non-embryogenic cells that originate from the provascular elements of the hypocotyl. A search for marker genes to monitor the transition of somatic into competent and embryogenic cells in established suspension cell cultures resulted in the identification of a gene transiently expressed in a small subpopulation of the same enlarged single cells that are formed during the initiation of the embryogenic cultures from hypocotyl explants. The predicted amino acid sequence and in vitro kinase assays show that this gene encodes a leucine-rich repeat containing receptor-like kinase protein, designated Somatic Embryogenesis Receptor-like Kinase (SERK). Somatic embryos formed from cells expressing a SERK promoter-luciferase reporter gene. During somatic embryogenesis, SERK expression ceased after the globular stage. In plants, SERK mRNA could only be detected transiently in the zygotic embryo up to the early globular stage but not in unpollinated flowers nor in any other plant tissue. These results suggest that somatic cells competent to form embryos and early globular somatic embryos share a highly specific signal transduction chain with the zygotic embryo from shortly after fertilization to the early globular embryo.