SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE Family Research Articles

Cloning and characterization of the SERK1 gene in triploid Pingyi Tiancha [Malus hupehensis (Pamp.) Rehd. var. pingyiensis Jiang] and a tetraploid hybrid strain

This study aims to explore the roles of somatic embryogenesis receptor-like kinase (SERK) in Malus hupehensis (Pingyi Tiancha). The full-length sequences of SERK1 in triploid Pingyi Tiancha (3n) and a tetraploid hybrid strain 33# (4n) were cloned, sequenced, and designated as MhSERK1 and MhdSERK1, respectively. Multiple alignments of amino acid sequences were conducted to identify similarity between MhSERK1 and MhdSERK1 and SERK sequences in other species, and a neighbor-joining phylogenetic tree was constructed to elucidate their phylogenetic relations. Expression levels of MhSERK1 and MhdSERK1 in different tissues and developmental stages were investigated using quantitative real-time PCR. The coding sequence lengths of MhSERK1 and MhdSERK1 were 1899 bp (encoding 632 amino acids) and 1881 bp (encoding 626 amino acids), respectively. Sequence analysis demonstrated that MhSERK1 and MhdSERK1 display high similarity to SERKs in other species, with a conserved intron/exon structure that is unique to members of the SERK family. Additionally, the phylogenetic tree showed that MhSERK1 and MhdSERK1 clustered with orange CitSERK (93%). Furthermore, MhSERK1 and MhdSERK1 were mainly expressed in the reproductive organs, in particular the ovary. Their expression levels were highest in young flowers and they differed among different tissues and organs. Our results suggest that MhSERK1 and MhdSERK1 are related to plant reproduction, and that MhSERK1 is related to apomixis in triploid Pingyi Tiancha.

Isolation and Expression Analysis of a SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) Gene in Curcuma alismatifolia Gagnep.

Somatic embryogenesis provides a useful tool to facilitate efficient mass propagation in plants. The SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) gene serves a fundamentally important role in somatic embryogenesis of many plant species. The isolation of a SERK gene homolog, namely CaSERK, from Curcuma alismatifolia Gagnep. cv. Blue Tung, was reported. Prediction of coding sequence showed that it encoded a protein of 628 amino acids showing high similarity to previously characterized SERK sequences and containing all the features shared by members of the SERK family, including five leucine-rich repeats and the distinctive proline-rich SPP domain. Investigation of CaSERK expression revealed that its transcripts were found throughout the whole somatic embryogenesis process with highest abundance in embryogenic callus. These results indicate that CaSERK might have somatic embryogenesis-associated functions in this economically important ornamental ginger. Detection of CaSERK transcript accumulation in flower and coma bract tissues is suggestive of its additional roles in other developmental signaling pathways.

Cloning and Characterization of a Somatic Embryogenesis Receptor-Like Kinase Gene in Cotton (Gossypium hirsutum)

A novel gene, GhSERK1, was identified in cotton. It encoded a protein belonging to the somatic embryogenesis receptorlike kinase (SERK) family. The genomic sequence of GhSERK1 was 6920 bp in length, containing a predicted transcriptional start site (TSS). Its full-length cDNA was 2502 bp, encoding a protein of 627 amino acids. Sequence analysis of GhSERK1 revealed high levels of similarity to other reported SERKs, as well as a conserved intron/exon structure that was unique to members of the SERK family. Expression analysis showed that GhSERK1 mRNA was present in all organs of cotton plants and at different developmental stages, but its transcripts were most abundant in reproductive organs. Compared with that of the male-fertile line, the level of GhSERK1 mRNA was lower in the anther of the male-sterile cotton line, in which the pollen development was defected. Taken together, these findings illustrated that the GhSERK1 play a critical role during the anther formation, and may also have a broad role in other aspects of plant development.

Characterization and expression analysis of AcSERK2, a somatic embryogenesis and stress resistance related gene in pineapple

The isolation and characterization of AcSERK2, another somatic embryogenesis receptor-like kinase (SERK) gene homolog, confirmed that there was a SERK gene family in pineapple. AcSERK2 shared high similarity to AcSERK1 and other SERKs, containing all the characteristic domains of the SERK family. The expressed recombinant protein of pET-AcSERK2 was soluble. AcSERK2 expression was effectively induced by 2,4-dichlorophenoxyacetic acid (2,4-D) and maintained in high level at the early stage of somatic embryogenesis (SE). The results of in situ hybridization showed that AcSERK2 expressed at high level in the competent cells under the induction of 2, 4-D and at low level during the development of meristematic center to globular embryo. This indicated that AcSERK2 could be used as a potential marker gene to monitor the acquisition of embryogenic competence. However, AcSERK2 expression was also detected in all the tested organs and the expression level decreased along with the development of calyx, ovule and ovary. These results suggested that AcSERK2 maybe play a broader role in organ development. AcSERK2 transcription could be induced by exogenous hormones and abiotic stress. It was deduced that AcSERK2 may participate in response to exogenous hormones and abiotic stress regulation in pineapple. The expression pattern of AcSERK2 during SE differed from that of AcSERK1, and this indicated that the SERK genes may be non-redundant in somatic embryogenesis.

Cloning and Molecular Characterization of a SERK Gene Transcriptionally Induced During Somatic Embryogenesis in Ananas comosus cv. Shenwan

A somatic embryogenesis receptor-like kinase (SERK) gene, designated as AcSERK1, was isolated from pineapple (Ananas comosus cv. Shenwan). AcSERK1 shared all the characteristic domains of the SERK family, including five leucine-rich repeats, one proline-rich region motif, transmembrane domain, and kinase domains. Somatic embryogenic cultures of pineapple were established following transfer of callus cultures to Murashige and Skoog (1962) medium containing 2,4-dichlorophenoxyacetic acid. The role of AcSERK1 during establishment of somatic embryogenesis in culture was investigated. The AcSERK1 was highly expressed during embryogenic competence acquisition and global embryo formation in culture. These findings were obtained along with morphological changes in callus cultures exhibiting embryogenic potential. Overall, levels of expression of AcSERK1 were lower in nonembryogenic tissues and organs than in embryogenic callus. In situ hybridization analysis revealed that AcSERK1 expression was detected in embryogenic tissues, including single competent cells, meristematic centers wherein embryogenic structures are formed, and global embryos. These results suggested that AcSERK1 expression was associated with induction of somatic embryogenesis and that it could be used as a potential marker gene to monitor the transition of pineapple callus tissues into competent and embryogenic cells and tissues.

Isolation and Functional Characterization of a SERK Gene from Soybean (Glycine max (L.) Merr.)

It is well accepted that somatic embryogenesis serves a primary role in plant regeneration. However, it is also a model system to explore the regulatory and morphogenetic events in the life of a plant. To date, a suite of genes that serve important roles in somatic embryogenesis have been isolated and identified. In the present study, a novel gene designated as GmSERK1 was isolated from soybean (Glycine max (L.) Merr). Sequence and structural analysis determined that the GmSERK1 protein, which encodes 624 amino acids, belongs to the somatic embryogenesis receptor-like kinase (SERK) gene family. GmSERK1 shared all the characteristic domains of the SERK family, including five leucine-rich repeats, one proline-rich region motif, transmembrane domain, and kinase domains. DNA gel blot analysis indicated that a single copy of the GmSERK1 gene resides in the soybean genome. The GmSERK1 tissue-specific and induced expression patterns were explored using quantitative real-time PCR. Dissimilar expression levels in various tissues under different treatments were found. In addition, transient expression experiments in onion epidermal cells indicated that the GmSERK1 protein was located on the plasma membrane. The results from this study suggested that GmSERK1, a member of the SERK gene family, exhibits a broader role in various aspects of plant development and function, in addition to its basic functions in somatic embryogenesis.

Cloning and molecular characterisation of a potato SERK gene transcriptionally induced during initiation of somatic embryogenesis

Somatic embryogenesis offers great potential in plant propagation, long-term germplasm conservation, and as a suitable model system for deciphering early events during embryogenesis. The up-regulation and ectopic expression of a SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) gene has been shown to mark and enhance embryogenic competence in somatic cells of model plant species. We have cloned and characterised a SERK gene (StSERK1) from potato (Solanum tuberosum L.), an important crop plant. Sequence analysis of StSERK1 revealed high levels of similarity to other plant SERKs, as well as a conserved intron/exon structure which is unique to members of the SERK family. Furthermore, StSERK clustered most closely with SERK gene family members such as MtSERK1, CuSERK1, AtSERK1, and DcSERK, implicated in evoking somatic embryogenesis. Monitoring of SERK expression during progression of potato somatic embryogenesis revealed increased StSERK expression during the induction phase. Subsequently, during the embryo transition phases, StSERK expression was unchanged and did not vary among embryo-forming and inhibitory conditions. However, in isolated somatic embryos StSERK expression was again up-regulated. In other plant parts (leaves, true potato seeds, microtubers and flower buds), StSERK showed different levels of expression. Expression analysis suggests that the isolated StSERK could be a functional SERK orthologue. The possible role of SERK as a marker of pluripotency, rather than embryogenesis alone, is discussed.

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.