Somatic Embryogenesis Receptor Kinase Research Articles

Rice NLR protein XinN1, induced by a pattern recognition receptor XA21, confers enhanced resistance to bacterial blight.

Rice CC-type NLR XinN1, specifically induced by a PRR XA21, activates defense pathways against Xoo. Plants have evolved two layers of immune systems regulated by two different types of immune receptors, cell surface located pattern recognition receptors (PRRs) and intracellular nucleotide-binding domain leucine-rich repeat-containing receptors (NLRs). Plant PRRs recognize conserved molecular patterns from diverse pathogens, resulting in pattern-triggered immunity (PTI), whereas NLRs are activated by effectors secreted by pathogens into plant cells, inducing effector-triggered immunity (ETI). Rice PRR, XA21, recognizes a tyrosine-sulfated RaxX peptide (required for activation of XA21-mediated immunity X) as a molecular pattern secreted by Xanthomonas oryzae pv. oryzae (Xoo). Here, we identified a rice NLR gene, XinN1, that is specifically induced during the XA21-mediated immune response against Xoo. Transgenic rice plants overexpressing XinN1 displayed increased resistance to infection by Xoo with reduced lesion length and bacterial growth. Overexpression of autoactive mutant of XinN1 (XinN1D543V) also displayed increased resistance to Xoo, accompanied with severe growth retardation and cell death. In rice protoplast system, overexpression of XinN1 or XinN1D543V significantly elevated reactive oxygen species (ROS) production and cytosolic-free calcium (Ca2+) accumulations. In addition, XinN1 overexpression additionally elevated the ROS burst caused by the interaction between XA21 and RaxX-sY and induced the transcription of PTI signaling components, including somatic embryogenesis receptor kinases (OsSERKs) and receptor-like cytoplasmic kinases (OsRLCKs). Our results suggest that XinN1 induced by the PRR XA21 activates defense pathways and provides enhanced resistance to Xoo in rice.

Control of lateral root formation by rapamycin-induced dimerization of engineered RGI/BAK1 and by BIR3 chimera.

Leucine-rich repeat receptor kinases (LRR-RKs) play a pivotal role in diverse aspects of growth, development, and immunity in plants by sensing extracellular signals. Typically, LRR-RKs are activated through the ligand-induced interaction with a SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) coreceptor, triggering downstream signaling. ROOT MERISTEM GROWTH FACTOR1 (RGF1) INSENSITIVEs (RGIs) LRR-RLK receptors promote primary root meristem activity while inhibiting lateral root (LR) development in response to RGF peptide. In this study, we employed rapamycin-induced dimerization (RiD) and BAK1-INTERACTING RECEPTOR-LIKE KINASE3 (BIR3) chimera approaches to explore the gain-of-function of RGI1, RGI4, and RGI5. Rapamycin induced the association of cytosolic kinase domains (CKDs) of RGI1 and the BAK1 coreceptor, activating both mitogen-activated protein kinase 3 (MPK3) and MPK6. Rapamycin significantly inhibited LR formation in RiD-RGI1/RGI4/RGI5-BAK1 plants. Using transgenic Arabidopsis expressing RGI1CKD fused to the BIR3-LRR chimera under estradiol control, we observed a substantial reduction in LR density upon β-estradiol treatment. Additionally, we identified a decrease in root gravitropism in BIR3 chimera plants. In contrast, RiD-RGI/BAK1 plants did not exhibit defects in root gravitropism, implying the importance of combinatorial interactions between RGIs and SERK coreceptors in the inhibition of root gravitropism. Constitutive activation of RGIs with BAK1 in RiD-RGI/BAK1 plants by rapamycin treatment resulted in the inhibition of primary root growth, resembling the inhibitory effects observed with high concentrations of phytohormones on primary root elongation. Our findings highlight that the interactions between CKDs of RGIs and BAK1, constitutively induced by rapamycin or BIR3 chimera, efficiently control LR development.

General Regulatory Factor7 regulates innate immune signalling to enhance Verticillium wilt resistance in cotton.

Sessile growing plants are always vulnerable to microbial pathogen attacks throughout their lives. To fend off pathogen invasion, plants have evolved a sophisticated innate immune system that consists of cell surface receptors and intracellular receptors. Somatic embryogenesis receptor kinases (SERKs) belong to a small group of leucine-rich repeat receptor-like kinases (LRR-RLKs) that function as co-receptors regulating diverse physiological processes. GENRAL REGULATORY FACTOR (GRF) proteins play an important role in physiological signalling transduction. However, the function of GRF proteins in plant innate immune signalling remains elusive. Here, we identified a GRF gene, GauGRF7, that is expressed both constitutively and in response to fungal pathogen infection. Intriguingly, silencing of GRF7 compromised plant innate immunity, resulting in susceptibility to Verticillium dahliae infection. Both transgenic GauGRF7 cotton and transgenic GauGRF7 Arabidopsis lines enhanced the innate immune response to V. dahliae infection, leading to high expression of two helper NLRs (hNLR) genes (ADR1 and NRG1) and pathogenesis-related genes, and increased ROS production and salicylic acid level. Moreover, GauGRF7 interacted with GhSERK1, which positively regulated GRF7-mediated innate immune response in cotton and Arabidopsis. Our findings revealed the molecular mechanism of the GRF protein in plant immune signaling and offer potential opportunities for improving plant resistance to V. dahliae infection.

BAK-up: the receptor kinase BAK-TO-LIFE 2 enhances immunity when BAK1 is lacking

BRI1-ASSOCIATED KINASE 1 (BAK1/SERK3) and its closest homolog BAK1-LIKE 1 (BKK1/SERK4) are leucine-rich repeat receptor kinases (LRR-RKs) belonging to the SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) family. They act as co-receptors of various other LRR-RKs and participate in multiple signaling events by complexing and transphosphorylating ligand-binding receptors. Initially identified as the brassinosteroid receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1) co-receptor, BAK1 also functions in plant immunity by interacting with pattern recognition receptors. Mutations in BAK1 and BKK1 cause severely stunted growth and cell death, characterized as autoimmune cell death. Several factors play a role in this type of cell death, including RKs and components of effector-triggered immunity (ETI) signaling pathways, glycosylation factors, ER quality control components, nuclear trafficking components, ion channels, and Nod-like receptors (NLRs). The Shan lab has recently discovered a novel RK BAK-TO-LIFE 2 (BTL2) that interacts with BAK1 and triggers cell death in the absence of BAK1 and BKK1. This RK compensates for the loss of BAK1-mediated pattern-triggered immunity (PTI) by activating phytocytokine-mediated immune and cell death responses.

The Leucine-Rich Repeat Receptor-Like Kinase Protein TaSERK1 Positively Regulates High-Temperature Seedling Plant Resistance to Puccinia striiformis f. sp. tritici by Interacting with TaDJA7.

Somatic embryogenesis receptor kinases (SERKs) belong to the leucine-rich repeat receptor-like kinase (LRR-RLK) subfamily, and many LRR-RLKs have been proven to play a key role in plant immune signal transmission. However, the functions of SERKs in resistance to stripe rust caused by Puccinia striiformis f. sp. tritici remains unknown. Here, we identified a gene, TaSERK1, from Xiaoyan 6, a wheat cultivar possessing high-temperature seedling-plant (HTSP) resistance to the fungal pathogen P. striiformis f. sp. tritici and expresses its resistance at the seedling stage. The expression level of TaSERK1 was upregulated upon P. striiformis f. sp. tritici inoculation under relatively high temperatures. The transcriptional level of TaSERK1 was significantly increased under exogenous salicylic acid and brassinosteroids treatments. The barley stripe mosaic virus-induced gene silencing assay indicated that TaSERK1 positively regulated the HTSP resistance to stripe rust. The transient expression of TaSERK1 in tobacco leaves confirmed its subcellular localization on the plasma membrane. Furthermore, TaSERK1 interacted with and phosphorylated the chaperone protein TaDJA7, which belongs to the heat shock protein 40 subfamily. Silencing TaDJA7 compromised the HTSP resistance to stripe rust. The results indicated that when the membrane immune receptor TaSERK1 perceives the P. striiformis f. sp. tritici infection under relatively high temperatures, it transmits the signal to TaDJA7 to activate HTSP resistance to the pathogen.

Screening genome-editing knockouts reveals the receptor-like kinase ASX role in regulations of secondary xylem development in Populus.

In trees, secondary xylem development is essential for the growth of perennial stem increments. Many signals regulate the process of development, but our knowledge of the molecular components involved in signal transduction is still limited. In this study, we identified Attenuation of Secondary Xylem (ASX) knockouts by screening genome-editing knockouts of xylem-expressed receptor-like kinases (RLKs) in Populus. The ASX role in secondary xylem development in Populus was discovered using biochemical, cellular, and genomic analyses. The ASX knockout plants had abnormal secondary stem growth but had little effect on shoot apical primary growth. ASX and SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK)2/4 were co-precipitated in developing xylem. Through their interaction, ASX is phosphorylated by SERK. Transcriptome analysis of developing xylem revealed that ASX deficiency inhibited the transcriptional activity of genes involved in xylem differentiation and secondary cell wall formation. By forming a complex, ASX and SERK may function as a signaling module for signal transduction required in the regulation of secondary xylem development in trees. This study shows that ASX, which encodes a RLKs, is required for secondary xylem development and sheds light on regulatory signals found in tree stem secondary growth.

An EPFL peptide signaling pathway promotes stamen elongation via enhancing filament cell proliferation to ensure successful self-pollination in Arabidopsis thaliana.

Proper stamen filament elongation is essential for plant self-pollination and reproduction. Several phytohormones such as jasmonate and gibberellin play important roles in controlling filament elongation, but other endogenous signals involved in this developmental process remain unknown. We report here that three EPIDERMAL PATTERNING FACTOR-LIKE (EPFL) family peptides, EPFL4, EPFL5 and EPFL6, act redundantly to promote stamen filament elongation via enhancing filament cell proliferation in Arabidopsis thaliana. Knockout of EPFL4-6 genes led to shortened filaments due to defective filament cell proliferation, resulting in pollination failure and male sterility. Further genetic and biochemical analyses indicated that the ERECTA family and the SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) family RLKs form receptor complexes to perceive EPFL4-6 peptides and promote filament cell proliferation. Moreover, based on both loss- and gain-of-function genetic analyses, the mitogen-activated protein kinase cascade MKK4/MKK5-MPK6 was shown to function downstream of EPFL4-6 to positively regulate cell proliferation in stamen filaments. Together, this study reveals that an EPFL peptide signaling pathway composed of the EPFL4-6 peptide ligands, the ERECTA-SERK receptor complexes and the downstream MKK4/MKK5-MPK6 cascade promotes stamen filament elongation via enhancing filament cell proliferation to ensure successful self-pollination and normal fertility in Arabidopsis.

The somatic embryogenesis receptor kinase TaSERK1 participates in the immune response to Rhizoctonia cerealis infection by interacting and phosphorylating the receptor-like cytoplasmic kinase TaRLCK1B in wheat

The sharp eyespot, caused by necrotrophic pathogen Rhizoctonia cerealis, often causes serious yield loss in wheat (Triticum aestivum). However, the mechanisms underlying wheat resistant responses to the pathogen are still limited. In this study, we performed a genome-wide analysis of somatic embryogenesis receptor kinase (SERK) family in wheat. As a result, a total of 26 TaSERK candidate genes were identified from the wheat genome. Only 6 TaSERK genes on the chromosomes 2A, 2B, 2D, 3A, 3B, and 3D showed obvious heightening expression patterns in resistant wheat infected with R. cerealis compared than those un-infected wheat. Of them, the transcripts of 3 TaSERK1 homoeologs on the chromosomes 2A, 2B, and 2D were significantly up-regulated in the highest level compared to other TaSERKs. Importantly, silencing of TaSERK1 significantly impaired wheat resistance to sharp eyespot. Further bio-molecular assays showed that TaSERK1 could interact with the defence-associated receptor-like cytoplasmic kinase TaRLCK1B, and phosphorylated TaRLCK1B. Together, the results suggest that TaSERK1 mediated resistance responses to R. cerealis infection by interacting and phosphorylating TaRLCK1B in wheat. This study sheds light on the understanding of the wheat SERKs in the innate immunity against R. cerealis, and provided a theoretical fulcrum to identify candidate resistant genes for improving wheat resistance against sharp eyespot in wheat.

Impact of Exogenous Application of Potato Virus Y-Specific dsRNA on RNA Interference, Pattern-Triggered Immunity and Poly(ADP-ribose) Metabolism.

In this work we developed and exploited a spray-induced gene silencing (SIGS)-based approach to deliver double-stranded RNA (dsRNA), which was found to protect potato against potato virus Y (PVY) infection. Given that dsRNA can act as a defence-inducing signal that can trigger sequence-specific RNA interference (RNAi) and non-specific pattern-triggered immunity (PTI), we suspected that these two pathways may be invoked via exogeneous application of dsRNA, which may account for the alterations in PVY susceptibility in dsRNA-treated potato plants. Therefore, we tested the impact of exogenously applied PVY-derived dsRNA on both these layers of defence (RNAi and PTI) and explored its effect on accumulation of a homologous virus (PVY) and an unrelated virus (potato virus X, PVX). Here, we show that application of PVY dsRNA in potato plants induced accumulation of both small interfering RNAs (siRNAs), a hallmark of RNAi, and some PTI-related gene transcripts such as WRKY29 (WRKY transcription factor 29; molecular marker of PTI), RbohD (respiratory burst oxidase homolog D), EDS5 (enhanced disease susceptibility 5), SERK3 (somatic embryogenesis receptor kinase 3) encoding brassinosteroid-insensitive 1-associated receptor kinase 1 (BAK1), and PR-1b (pathogenesis-related gene 1b). With respect to virus infections, PVY dsRNA suppressed only PVY replication but did not exhibit any effect on PVX infection in spite of the induction of PTI-like effects in the presence of PVX. Given that RNAi-mediated antiviral immunity acts as the major virus resistance mechanism in plants, it can be suggested that dsRNA-based PTI alone may not be strong enough to suppress virus infection. In addition to RNAi- and PTI-inducing activities, we also showed that PVY-specific dsRNA is able to upregulate production of a key enzyme involved in poly(ADP-ribose) metabolism, namely poly(ADP-ribose) glycohydrolase (PARG), which is regarded as a positive regulator of biotic stress responses. These findings offer insights for future development of innovative approaches which could integrate dsRNA-induced RNAi, PTI and modulation of poly(ADP-ribose) metabolism in a co-ordinated manner, to ensure a high level of crop protection.

Analysis of Grapevine's Somatic Embryogenesis Receptor Kinase (SERK) Gene Family: VqSERK3/BAK1 Overexpression Enhances Disease Resistance.

The somatic embryogenesis receptor kinase (SERK) gene family has been intensively studied in several plant species. Here we confirmed the existence of five SERK genes in grapevine (Chinese wild grapevine Vitis quinquangularis) and named them VqSERK1, VqSERK2, VqSERK3, VqSERK4, and VqSERK5. Analysis of the predicted structures of these SERK proteins revealed they include a signal peptide domain, a leucine zipper domain, a Ser-Pro-Pro domain, a single transmembrane domain, different leucine-rich repeats, and an intracellular kinase activity domain. The SERK genes of grapevine showed different gene expression patterns when treated with powdery mildew (Erysiphe necator) and hormones (salicylic acid, jasmonic acid, abscisic acid, and ethylene). Subcellular localization assays confirmed that VqSERK family proteins localized to the cell membrane. Moreover, we cloned the SERK3/BAK1 gene from the Chinese wild grapevine V. quinquangularis clone 'Shang-24'. Heterologous VqSERK3/BAK1 expression in the Arabidopsis bak1-4 mutant lines restored control of cell death, increased resistance to powdery mildew, and strengthened stomatal immunity. Our work may provide the foundation for further studies of SERK genes for pathogen resistance and hormone treatment in grapevine.

A novel leucine-rich repeat receptor-like kinase MRK1 regulates resistance to multiple stresses in tomato.

Leucine-rich repeat receptor-like kinases (LRR-RLKs) are ubiquitous in higher plants and act as receptors of extracellular signals to trigger multiple physiological processes. However, the functions of the majority of LRR-RLKs remain largely unknown, especially in tomato (Solanum lycopersicum L.). Here, we found that MRK1 (Multiple resistance-associated kinase 1), encoding a novel tomato LRR-RLK, was significantly induced by temperature stresses and bacterial pathogen attacks. Knocking out MRK1 impaired tolerance to both cold and heat stress, accompanied by decreased transcript levels of the master regulators C-repeat binding factor 1 (CBF1) and Heat shock transcription factor a-1a (HsfA1a), respectively. In addition, mrk1 mutants were hypersensitive to Pseudomonas syringae pv. tomato DC3000 and Ralstonia solanacearum and showed compromised pattern-triggered immunity (PTI) responses, as evidenced by decreased production of reactive oxygen species and reduced upregulation of PTI marker genes. Moreover, bimolecular fluorescence complementation, split-luciferase assays, and co-immunoprecipitation supported the formation of a complex of MRK1, FLS2, and Somatic embryogenesis receptor kinase (SERK3A/SERK3B) in a ligand-independent manner. This work demonstrates that tomato MRK1 is a novel positive regulator of multiple stress responses and may be a potential breeding target for improving crop stress resistance.

Comparative proteomic analysis provides new insights into regulation of microspore embryogenesis induction in winter triticale (\xd7\u2009Triticosecale Wittm.) after 5-azacytidine treatment

Effective microspore embryogenesis (ME) requires substantial modifications in gene expression pattern, followed by changes in the cell proteome and its metabolism. Recent studies have awakened also interest in the role of epigenetic factors in microspore de-differentiation and reprogramming. Therefore, demethylating agent (2.5–10 μM 5-azacytidine, AC) together with low temperature (3 weeks at 4 °C) were used as ME-inducing tiller treatment in two doubled haploid (DH) lines of triticale and its effect was analyzed in respect of anther protein profiles, expression of selected genes (TAPETUM DETERMINANT1 (TaTPD1-like), SOMATIC EMBRYOGENESIS RECEPTOR KINASE 2 (SERK2) and GLUTATHIONE S-TRANSFERASE (GSTF2)) and ME efficiency. Tiller treatment with 5.0 µM AC was the most effective in ME induction; it was associated with (1) suppression of intensive anabolic processes-mainly photosynthesis and light-dependent reactions, (2) transition to effective catabolism and mobilization of carbohydrate reserve to meet the high energy demand of cells during microspore reprograming and (3) effective defense against stress-inducing treatment, i.e. protection of proper folding during protein biosynthesis and effective degradation of dysfunctional or damaged proteins. Additionally, 5.0 µM AC enhanced the expression of all genes previously identified as being associated with embryogenic potential of microspores (TaTPD1-like, SERK and GSTF2).

The Arabidopsis MIK2 receptor elicits immunity by sensing a conserved signature from phytocytokines and microbes

Sessile plants encode a large number of small peptides and cell surface-resident receptor kinases, most of which have unknown functions. Here, we report that the Arabidopsis receptor kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) recognizes the conserved signature motif of SERINE-RICH ENDOGENOUS PEPTIDEs (SCOOPs) from Brassicaceae plants as well as proteins present in fungal Fusarium spp. and bacterial Comamonadaceae, and elicits various immune responses. SCOOP signature peptides trigger immune responses and altered root development in a MIK2-dependent manner with a sub-nanomolar sensitivity. SCOOP12 directly binds to the extracellular leucine-rich repeat domain of MIK2 in vivo and in vitro, indicating that MIK2 is the receptor of SCOOP peptides. Perception of SCOOP peptides induces the association of MIK2 and the coreceptors SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3 (SERK3) and SERK4 and relays the signaling through the cytosolic receptor-like kinases BOTRYTIS-INDUCED KINASE 1 (BIK1) and AVRPPHB SUSCEPTIBLE1 (PBS1)-LIKE 1 (PBL1). Our study identifies a plant receptor that bears a dual role in sensing the conserved peptide motif from phytocytokines and microbial proteins via a convergent signaling relay to ensure a robust immune response.

Perception of the pathogen-induced peptide RGF7 by the receptor-like kinases RGI4 and RGI5 triggers innate immunity in Arabidopsis thaliana.

Signaling peptides play crucial roles in plant growth, development and defense. We report here that the Arabidopsis thaliana secreted peptide, ROOT MERISTEM GROWTH FACTOR 7 (RGF7), functions as an endogenous elicitor to trigger plant immunity. Expression of the RGF7 precursor-encoding gene (preRGF7) is highly induced in Arabidopsis leaves upon infection by the bacterial pathogen Pseudomonas syringae. The pathogen-responsive preRGF7 expression is regulated by the transcription factor WRKY33 and its upstream mitogen-activated protein kinases MPK3/MPK6 and calcium-dependent protein kinases CPK5/CPK6. In the absence of pathogen attack, chemically induced expression of preRGF7 in transgenic Arabidopsis plants was sufficient to trigger immune responses. Pre-induction of preRGF7 expression in transgenic Arabidopsis also led to enhanced immune responses and increased resistance to P.syringae infection. Biochemical and genetic analyses demonstrated that RGF7 is perceived by the leaf-expressed RGF1 INSENSITIVE (RGI) family receptors RGI4 and RGI5. The SOMATIC EMBRYOGENESIS RECEPTOR KINASES (SERKs) BAK1 and SERK4 are also involved in RGF7 perception via forming RGF7-induced receptor-complexes with RGI4 and RGI5. These results indicate that the pathogen-induced RGF7 peptide, perceived by the RGI4/RGI5-BAK1/SERK4 receptor complexes, acts as a new damage-associated molecular pattern (DAMP) and plays a significant role in Arabidopsis immunity.

BRI1 Signaling in the Root is Mediated through the SERK1 and SERK3 Co-receptors

Brassinosteroid (BR) is a class of polyhydroxysteroids plant hormones known to regulate shoot and root growth. Genetic and molecular analyses demonstrate that receptor kinase BRI1 protein acts as a perceiver for BR. One of the characteristics of bri1 mutant’s phenotypes is the complete BR insensitivity in the root. Biochemical evidences of the BRI1 protein complex indicates that somatic embryogenesis receptor kinase 1 (SERK1) and SERK3 participate in the BR pathway in Arabidopsis root. While only serk3 mutants show partial reduction to BR sensitivity, serk1 presents a normal BR penetration phenotype compared to the wild type. Interestingly, the double mutant serk1serk3 displays more, but not full resistance to BR in root length assay. In this study, we aimed to enhance the BR insensitivity of the double mutant serk1serk3 by crossing serk1 mutant allele with a strong serk3 and bri1 mutant alleles. In our study, by generating serk1-3serk3-2 double mutants, a complete insensitivity to BR that phenocopied bri1-301 mutant was recorded. However, we were unable to increase BR resistance in the root of serk1-3serk3-2 double mutant by crossing with bri1 mutant allele in the triple mutant serk1-3serk3-2bri1. As a result, all the BRI1 signaling in the root was mediated through the SERK1 and SERK3 co-receptors. Additionally, we established that based on conventional BR assays, the At1g27190 protein was also involved in BR signaling. Preliminary data indicated that the triple mutant serk1serk3-2At1g27190 showed a dwarfed phenotype. Whether or not this dwarfed phenotype is linked to BRI1 signaling impairment needs to be further investigated.

Transcriptome analysis identifies genes involved in the somatic embryogenesis of Eucalyptus

BackgroundEucalyptus, a highly diverse genus of the Myrtaceae family, is the most widely planted hardwood in the world due to its increasing importance for fiber and energy. Somatic embryogenesis (SE) is one large-scale method to provide commercial use of the vegetative propagation of Eucalyptus and dedifferentiation is a key step for plant cells to become meristematic. However, little is known about the molecular changes during the Eucalyptus SE.ResultsWe compared the transcriptome profiles of the differentiated and dedifferentiated tissues of two Eucalyptus species – E. camaldulensis (high embryogenetic potential) and E. grandis x urophylla (low embryogenetic potential). Initially, we identified 18,777 to 20,240 genes in all samples. Compared to the differentiated tissues, we identified 9229 and 8989 differentially expressed genes (DEGs) in the dedifferentiated tissues of E. camaldulensis and E. grandis x urophylla, respectively, and 2687 up-regulated and 2581 down-regulated genes shared. Next, we identified 2003 up-regulated and 1958 down-regulated genes only in E. camaldulensis, including 6 somatic embryogenesis receptor kinase, 17 ethylene, 12 auxin, 83 ribosomal protein, 28 zinc finger protein, 10 heat shock protein, 9 histone, 122 cell wall related and 98 transcription factor genes. Genes from other families like ABA, arabinogalactan protein and late embryogenesis abundant protein were also found to be specifically dysregulated in the dedifferentiation process of E. camaldulensis. Further, we identified 48,447 variants (SNPs and small indels) specific to E. camaldulensis, including 13,434 exonic variants from 4723 genes (e.g., annexin, GN, ARF and AP2-like ethylene-responsive transcription factor). qRT-PCR was used to confirm the gene expression patterns in both E. camaldulensis and E. grandis x urophylla.ConclusionsThis is the first time to study the somatic embryogenesis of Eucalyptus using transcriptome sequencing. It will improve our understanding of the molecular mechanisms of somatic embryogenesis and dedifferentiation in Eucalyptus. Our results provide a valuable resource for future studies in the field of Eucalyptus and will benefit the Eucalyptus breeding program.

Leucine-rich repeat receptor-like kinase II phylogenetics reveals five main clades throughout the plant kingdom.

SUMMARYReceptor‐like kinases (RLKs) represent the largest group of cell surface receptors in plants. The monophyletic leucine‐rich repeat (LRR)‐RLK subfamily II is considered to contain the somatic embryogenesis receptor kinases (SERKs) and NSP‐interacting kinases known to be involved in developmental processes and cellular immunity in plants. There are only a few published studies on the phylogenetics of LRR‐RLKII; unfortunately these suffer from poor taxon/gene sampling. Hence, it is not clear how many and what main clades this family contains, let alone what structure–function relationships exist. We used 1342 protein sequences annotated as ‘SERK’ and ‘SERK‐like’ plus related sequences in order to estimate phylogeny within the LRR‐RLKII clade, using the nematode protein kinase Pelle as an outgroup. We reconstruct five main clades (LRR‐RLKII 1–5), in each of which the main pattern of land plant relationships re‐occurs, confirming previous hypotheses that duplication events happened in this gene subfamily prior to divergence among land plant lineages. We show that domain structures and intron–exon boundaries within the five clades are well conserved in evolution. Furthermore, phylogenetic patterns based on the separate LRR and kinase parts of LRR‐RLKs are incongruent: whereas the LRR part supports a LRR‐RLKII 2/3 sister group relationship, the kinase part supports clades 1/2. We infer that the kinase part includes few ‘radical’ amino acid changes compared with the LRR part. Finally, our results confirm that amino acids involved in each LRR‐RLKII–receptor complex interaction are located at N‐capping residues, and that the short amino acid motifs of this interaction domain are highly conserved throughout evolution within the five LRR‐RLKII clades.

The Rice Xa3 Gene Confers Resistance to Xanthomonas oryzae pv. oryzae in the Model Rice Kitaake Genetic Background.

The rice XA21 and XA3 pattern receptor kinases, derived from Oryza longistaminata and an Oryza. sativa japonica cultivar Wase Aikoku 3, respectively, confer resistance to strains of the Gram-negative bacterium Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of rice bacterial blight disease. Previously, we showed that transfer of Xa21 to the model rice cultivar Kitaake enhances resistance to Xoo. In this manuscript we demonstrate that Kitaake expressing Xa3 confers resistance to Xoo strain PXO79 and that the stress-related marker genes PR10b and KO5 are upregulated in Xoo-infected Xa3 rice leaves. We also show that rice somatic embryogenesis receptor kinase 2 (OsSERK2) positively regulates XA3-mediated immunity in Kitaake. We found that overexpression of XA21 binding protein 15 (XB15) and XB24, two negative regulators of XA21-mediated immunity, do not affect XA3-mediated immunity in the Kitaake genetic background. Our results indicate that the rice immune receptors XA21 and XA3 employ both shared and distinct signaling components in their response to Xoo. The results are important to further understand pathogen-associated molecular pattern (PAMP)-triggered immunity in rice. Furthermore, the presence of Kitaake rice carrying Xa3 will facilitate genetic research to study the XA3-mediated immunity.

Genome wide characterization of the SERK/SERL gene family in Phalaenopsis equestris, Dendrobium catenatum and Apostasia shenzhenica (Orchidaceae)

Somatic embryogenesis receptor kinases (SERKs) play a significant role in morphogenesis, stress/defense and signal transduction. In the present study, we have identified two SERK and 11 SERK-like (SERL) genes in Phalaenopsis equestris, two SERK and 11 SERL genes in Dendrobium catenatum, and one SERK and eight SERL genes in Apostasia shenzhenica genome. Characterization of the SERK proteins revealed the presence of a signal peptide, a leucine zipper, five leucine-rich repeats (LRRs), a serine proline proline (SPP) motif, a transmembrane region, a kinase domain, and a C-terminus. Most of the SERK/SERL proteins were characterized with similar physicochemical properties. The presence of transmembrane region predicted their membranous localization. Tertiary structure prediction of all the five identified SERK proteins had sequence identity with BAK1 protein of Arabidopsis thaliana. Generally, all the SERK/SERL genes shared similar gene architecture and intron phasing. Gene ontology analysis indicated the role of SERKs in receptor and ATP binding, signal transduction, and protein phosphorylation. Phylogenetic analysis revealed the clustering of SERKs and SERLs in distinct clades. Expression of SERKs in reproductive tissues like floral bud, floral stalk, whole flower and pollen was reported to be higher than their expression in vegetative tissues with an exception of PeSERK1 and DcSERK1 which showed higher expression in leaves and roots, respectively. Likewise, a higher expression of AsSERK1 was observed in tubers. However, lower expression of SERLs was observed in majority of tissues studied irrespective of their vegetative or reproductive origin. This work paves way for future studies involving functional characterization of SERK/SERLs and their potential role in embryogenesis/organogenesis as an aid to regeneration and multiplication of endangered orchids.

Expression of Somatic Embryogenesis Receptor Kinase (SERK) gene and its regulation under the influence of exogenous additives duringin vitrosomantic embryo development in medicinal plants

Somatic embryogenesis is a process whereby a single cell or a group of cells are induced to form totipotent embryogenic cells. Somatic embryogenesis always served as a model system for studying the molecular mechanisms underlying the embryogenic developmental process. There is an upsurge of interest in scientists to explore the molecular understanding of embryogenesis and the involvement of different genes and proteins during this developmental process. Studies have shown that somatic embryogenesis is under a stringent coordinated control of some regulatory genes among which somatic embryogenesis receptor kinase (SERK) gene has claimed an important role. In recent time expression ofSERKgene was identified in embryogenic cultures of many higher plants indicating its positive role in embryogenic development. Studying the impact ofSERKgene on somatic as well as zygotic embryogenesis shall improve the understanding of the molecular events leading to the formation of embryogenic cultures. The review highlights the correlation ofSERKgene expression during somatic embryogenesis process and diverse functions ofSERKgene during developmental changes in plants.