SERK基因家族的研究进展

体细胞胚发生相关类受体蛋白激酶(SERK)基因相继地在胡萝卜、拟南芥、水稻等多种植物中克隆和表达, 并被证实是植物界中广泛存在的结构保守基因家族。SERK基因不仅在胚性组织中表达, 还在非胚性组织中表达, 参与了植物胚胎发育、雄性发育、病害防御和信号传导等活动。     

Role of SERK genes in plant environmental response

In plants, cell signaling connects the environmental input to the intracellular responses in plants. Exogenous signals play an important role in cell metabolism leading to growth and defense responses. Some of these stimuli induce anatomical and physiological modifications that are generally modulated by gene expression. SERK belongs to a small family of genes that code for a transmembrane protein involved in signal transduction and that have been strongly associated with somatic embryogenesis and apomixis in a number of plant species. Recent studies corroborate its role in somatic embryogenesis and suggest a broader range of functions in plant response to biotic and abiotic stimuli. This mini-review aims to present new data on SERK and discuss its involvement in plant development as well as in response to environmental stress.Key words: SERK, fungus tolerance, environmental stress, brassinosteroids, SAR     

The Arabidopsis leucine-rich repeat receptor-like kinases BAK1/SERK3 and BKK1/SERK4 are required for innate immunity to hemibiotrophic and biotrophic pathogens

Recognition of pathogen-associated molecular patterns (PAMPs) by surface-localized pattern recognition receptors (PRRs) constitutes an important layer of innate immunity in plants. The leucine-rich repeat (LRR) receptor kinases EF-TU RECEPTOR (EFR) and FLAGELLIN SENSING2 (FLS2) are the PRRs for the peptide PAMPs elf18 and flg22, which are derived from bacterial EF-Tu and flagellin, respectively. Using coimmunoprecipitation and mass spectrometry analyses, we demonstrated that EFR and FLS2 undergo ligand-induced heteromerization in planta with several LRR receptor-like kinases that belong to the SOMATIC-EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) family, including BRASSINOSTEROID INSENSITIVE1-ASSOCIATED KINASE1/SERK3 (BAK1/SERK3) and BAK1-LIKE1/SERK4 (BKK1/SERK4). Using a novel bak1 allele that does not exhibit pleiotropic defects in brassinosteroid and cell death responses, we determined that BAK1 and BKK1 cooperate genetically to achieve full signaling capability in response to elf18 and flg22 and to the damage-associated molecular pattern AtPep1. Furthermore, we demonstrated that BAK1 and BKK1 contribute to disease resistance against the hemibiotrophic bacterium Pseudomonas syringae and the obligate biotrophic oomycete Hyaloperonospora arabidopsidis. Our work reveals that the establishment of PAMP-triggered immunity (PTI) relies on the rapid ligand-induced recruitment of multiple SERKs within PRR complexes and provides insight into the early PTI signaling events underlying this important layer of plant innate immunity.     

Expression of SERK family receptor-like protein kinase genes in rice

Some SERK-family receptor-like protein kinase genes have been shown to confer embryonic competence to cells. In this study, we isolated two novel rice genes, OsSERK1 and OsSERK2, belonging to the SERK-family. OsSERK2 showed constitutive expression. The OsSERK1 promoter showed reporter gene activities in some specific tissues in a germinating seed, leaf and root, but not in a developing embryo. This promoter activity suggests that OsSERK1 may have roles in non-embryonic tissues rather than in the embryo.     

Two SERK genes are markers of pluripotency in Cyclamen persicum Mill

The genetic basis of stem cell specification in somatic embryogenesis and organogenesis is still obscure. SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) genes are involved in embryogenesis and organogenesis in numerous species. In vitro culture of Cyclamen persicum immature ovules provides a system for investigating stem cell formation and maintenance, because lines forming either organs or embryos or callus without organs/embryos are available for the same cultivar and plant growth regulator conditions. The present aim was to exploit this property of cyclamen cultures to understand the role of SERK(s) in stem cell formation and maintenance in somatic embryogenesis and organogenesis in vitro, in comparison with expression in planta. CpSERK1 and CpSERK2 were isolated from embryogenic callus. CpSERK1 and CpSERK2 levels by RT-PCR showed that expression is high in embryogenic, moderate in organogenic, and null in recalcitrant calli. in situ hybridizations showed that the expression of both genes started in clumps of pluripotent stem cells, from which both pre-embryogenic aggregates and organ meristemoids derived, and continued in their trans-amplifying, meristem-like, derivatives. Expression declined in organ meristemoids, in parallel with a partial loss of meristematization. In mature somatic embryos, and in shoot and root primordia, CpSERK1 and CpSERK2 were expressed in meristems, and similar patterns occurred in zygotic embryo and primary meristems in planta. The results point to SERK1 and SERK2 as markers of pluripotency in cyclamen. It is proposed that the high expression of these genes in the trans-amplifying derivatives of the stem cells maintains a pluripotent condition leading to totipotency and, consequently, somatic embryogenesis.     

Diverse roles of SERK family genes in plant growth,development and defense response

Plant receptor-like protein kinases (RLKs) are transmembrane proteins with an extracellular domain and an intracellular kinase domain, which enable plant perceiving diverse extracellular stimuli to trigger the intracellular signal transduction. The somatic embryogenesis receptor kinases (SERKs) code the leucine-rich-repeat receptor-like kinase (LRR-RLK), and have been demonstrated to associate with multiple ligand-binding receptors to regulate plant growth, root development, male fertility, stomatal development and movement, and immune responses. Here, we focus on the progress made in recent years in understanding the versatile functions of Arabidopsis SERK proteins, and review SERK proteins as co-receptor to perceive different endogenous and environmental cues in different signaling pathway, and discuss how the kinase activity of SERKs is regulated by various modification.     

体细胞胚胎发生相关类受体蛋白激酶基因(SERK)的研究进展

植物体内存在一个编码富亮氨酸重复受体蛋白激酶、与体细胞胚胎发生相关的类受体蛋白激酶基因(SERK)大家族,其在旱期胚胎、小孢子、成熟胚珠和维管组织中表达.文章从SERK的结构、编码的蛋白、基因表达、功能以及信号转导介绍了SERK的研究进展.     

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.     

Brassinosteroid-independent functions of the BRI1-associated kinase BAK1/SERK3

Eukaryotes have evolved programmed cell death (PCD) mechanisms that play important roles in both, development and immunity.^1–3 We demonstrated a requirement for the Arabidopsis thaliana leucine-rich repeat receptor-like kinase (LRR-RLK), BAK1/SERK3 (BRI1-Associated receptor Kinase 1/Somatic Embryogenesis Receptor Kinase 3) in regulating the containment of microbial infection-induced necrosis. BAK1-deficient plants showed constitutive expression of defense-related genes and developed spreading cell death upon infection by necrotizing pathogens that result in enhanced susceptibility to necrotrophic pathogens. This reaction was not inducible by exposition of bak1 mutants to general stresses but appeared to be solely inducible by necrotizing pathogen infection. BAK1 is known to interact with the brassinosteroid receptor, BRI1, and thereby facilitates plant growth and development in a brassinolide (BL)-dependent manner.^4,5 Surprisingly, the cell death-related phenotype in bak1 mutants is brassinolide-independent. In this addendum we want to present recent new data on BAK1 and discuss its role as a general regulator in plant processes being as diverse as brassinosteroid signaling in development, perception of pathogen associated molecular patterns (PAMPs), and cell-death control in innate immunity.Key words: LRR-RLK, cell-death control, immunity, brassinosteroids, BAK1, SERK3, BRI1, FLS2     

The SERK1 receptor‐like kinase regulates organ separation in Arabidopsis flowers

Through a sensitized screen for novel components of pathways regulating organ separation in Arabidopsis flowers, we have found that the leucine‐rich repeat receptor‐like kinase SOMATIC EMBRYOGENESIS RECEPTOR‐LIKE KINASE1 (SERK1) acts as a negative regulator of abscission. Mutations in SERK1 dominantly rescue abscission in flowers without functional NEVERSHED (NEV), an ADP‐ribosylation factor GTPase‐activating protein required for floral organ shedding. We previously reported that the organization of the Golgi apparatus and location of the trans‐Golgi network (TGN) are altered in nev mutant flowers. Disruption of SERK1 restores Golgi structure and the close association of the TGN in nev flowers, suggesting that defects in these organelles may be responsible for the block in abscission. We have also found that the abscission zones of nev serk1 flowers are enlarged compared to wild‐type. A similar phenotype was previously observed in plants constitutively expressing a putative ligand required for organ separation, INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), suggesting that signalling through IDA and its proposed receptors, HAESA and HAESA‐LIKE2, may be deregulated in nev serk1 abscission zone cells. Our studies indicate that in addition to its previously characterized roles in stamen development and brassinosteroid perception, SERK1 plays a unique role in modulating the loss of cell adhesion that occurs during organ abscission.     

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 (omatic mbryogenesis eceptor-like inase) 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. Received: 20 June 2000 / Accepted: 25 September 2000     

Characterization and expression analysis of SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) genes in sexual and apomictic Paspalum notatum

The SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) gene plays a fundamental role in somatic embryogenesis of angiosperms, and is associated with apomixis in Poa pratensis. The objective of this work was to isolate, characterize and analyze the expression patterns of SERK genes in apomictic and sexual genotypes of Paspalum notatum. A conserved 200-bp gene fragment was amplified from genomic DNA with heterologous primers, and used to initiate a chromosomal walking strategy for cloning the complete sequence. This procedure allowed the isolation of two members of the P. notatum SERK family; PnSERK1, which is similar to PpSERK1, and PnSERK2, which is similar to ZmSERK2 and AtSERK1. Phylogenetic analyses indicated that PnSERK1 and PnSERK2 represent paralogous sequences. Southern-blot hybridization indicated the presence of at least three copies of SERK genes in the species. qRT-PCR analyses revealed that PnSERK2 was expressed at significantly higher levels than PnSERK1 in roots, leaves, reproductive tissues and embryogenic calli. Moreover, in situ hybridization experiments revealed that PnSERK2 displayed a spatially and chronologically altered expression pattern in reproductive organs of the apomictic genotype with respect to the sexual one. PnSERK2 is expressed in nucellar cells of the apomictic genotype at meiosis, but only in the megaspore mother cell in the sexual genotype. Therefore, apomixis onset in P. notatum seems to be correlated with the expression of PnSERK2 in nucellar tissue.     

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.     

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. Received: 14 May 1999 / Revision received: 27 August 1999 / Accepted: 8 September 1999