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Rice blast is one of the most devastating diseases, causing a significant reduction in global rice production. Developing and utilizing resistant varieties has proven to be the most efficient and cost-effective approach to control blasts. However, due to environmental pressure and intense pathogenic selection, resistance has rapidly broken down, and more durable resistance genes are being discovered. In this paper, a novel wall-associated kinase (WAK) gene, Pb4, which confers resistance to rice blast, was identified through a genome-wide association study (GWAS) utilizing 249 rice accessions. Pb4 comprises an N-terminal signal peptide, extracellular GUB domain, EGF domain, EGF-Ca2+ domain, and intracellular Ser/Thr protein kinase domain. The extracellular domain (GUB domain, EGF domain, and EGF-Ca2+ domain) of Pb4 can interact with the extracellular domain of CEBiP. Additionally, its expression is induced by chitin and polygalacturonic acid. Furthermore, transgenic plants overexpressing Pb4 enhance resistance to rice blast. In summary, this study identified a novel rice blast-resistant gene, Pb4, and provides a theoretical basis for understanding the role of WAKs in mediating rice resistance against rice blast disease. [ABSTRACT FROM AUTHOR]

The wall-associated kinases (WAKs) can perceive and transmit extracellular signals as one kind of unique receptor-like kinases (RLKs) involved in the regulation of cell expansion, pathogen resistance and abiotic stress tolerance. To understand their potential roles and screen some key candidates in Medicago truncatula (M. truncatula), genome-wide identification and characterization of MtWAKs were conducted in this study. A total of 54 MtWAK genes were identified and classified into four groups based on their protein domains. They were distributed on all chromosomes, while most of them were clustered on chromosome 1 and 3. The synteny analysis showed that 11 orthologous pairs were identified between M. truncatula and Arabidopsis thaliana (A. thaliana) and 31 pairs between M. truncatula and Glycine max (G. max). The phylogenetic analysis showed that WAK-RLKs were classified into five clades, and they exhibited a species-specific expansion. Most MtWAK-RLKs had similar exon–intron organization and motif distribution. Multiple cis-acting elements responsive to phytohormones, stresses, growth and development were observed in the promoter regions of MtWAK-RLKs. In addition, the expression patterns of MtWAK-RLKs varied with different plant tissues, developmental stages and biotic and abiotic stresses. Interestingly, plasm membrane localized MtWAK24 significantly inhibited Phytophthora infection in tobacco. The study provides valuable information for characterizing the molecular functions of MtWAKs in regulation of plant growth, development and stress tolerance in legume plants. [ABSTRACT FROM AUTHOR]

Abstract Background Wall-associated kinase (WAK)/WAK-like (WAKL) is one of the subfamily of receptor like kinases (RLK). Although previous studies reported that WAK/WAKL played an important role in plant cell elongation, response to biotic and abiotic stresses, there are no systematic studies on RcWAK/RcWAKL in rose. Results In this study, we identified a total of 68 RcWAK/RcWAKL gene family members within rose (Rosa chinensis) genome. The RcWAKs contained the extracellular galacturonan-binding domain and calcium-binding epidermal growth factor (EGF)-like domain, as well as an intracellular kinase domains. The RcWAKLs are missing either calcium-binding EGF-like domain or the galacturonan-binding domain in their extracellular region. The phylogenetic analysis showed the RcWAK/RcWAKL gene family has been divided into five groups, and these RcWAK/RcWAKL genes were unevenly distributed on the 7 chromosomes of rose. 12 of RcWAK/RcWAKL genes were significantly up-regulated by Botrytis cinerea-inoculated rose petals, where RcWAK4 was the most strongly expressed. Virus induced gene silencing of RcWAK4 increased the rose petal sensitivity to B. cinerea. The results indicated RcWAK4 is involved in the resistance of rose petal against B. cinerea. Conclusion Our study provides useful information to further investigate the function of the RcWAK/RcWAKL gene family and breeding research for resistance to B. cinerea in rose.

Abstract Background Verticillium wilt, caused by the soil borne fungus Verticillium dahliae, is a major threat to cotton production worldwide. An increasing number of findings indicate that WAK genes participate in plant−pathogen interactions, but their roles in cotton resistance to V. dahliae remain largely unclear. Results Here, we carried out a genome-wide analysis of WAK gene family in Gossypium hirsutum that resulted in the identification of 81 putative GhWAKs, which were all predicated to be localized on plasma membrane. In which, GhWAK77 as a representative was further located in tobacco epidermal cells using transient expression of fluorescent fusion proteins. All GhWAKs could be classified into seven groups according to their diverse protein domains, indicating that they might sense different outside signals to trigger intracellular signaling pathways that were response to various environmental stresses. A lot of cis-regulatory elements were predicted in the upstream region of GhWAKs and classified into four main groups including hormones, biotic, abiotic and light. As many as 28 GhWAKs, playing a potential role in the interaction between cotton and V. dahliae, were screened out by RNA-seq and qRT-PCR. To further study the function of GhWAKs in cotton resistance to V. dahliae, VIGS technology was used to silence GhWAKs. At 20 dpi, VIGSed plants exhibited more chlorosis and wilting than the control plants. The disease indices of VIGSed plants were also significantly higher than those of the control. Furthermore, silencing of GhWAKs significantly affected the expression of JA- and SA-related marker genes, increased the spread of V. dahliae in the cotton stems, dramatically compromised V. dahliae-induced accumulation of lignin, H2O2 and NO, but enhanced POD activity. Conclusion Our study presents a comprehensive analysis on cotton WAK gene family for the first time. Expression analysis and VIGS assay provided direct evidences on GhWAKs participation in the cotton resistance to V. dahliae.

The plant cell wall is a flexible physical barrier surrounding the cell which functions in growth and differentiation, signaling, and response to environmental stimuli including the Earth gravity force. In the present study, structural and molecular modifications of cell wall components of cultured tobacco (Nicotiana tabacum cv. Burley 21) cells under alternative gravity conditions induced by 7 days exposure to 2-D clinostat have been investigated. In comparison with the control group, clinorotation significantly increased biomass but reduced the total amounts of wall and the contents of cellulose, pectin, uronic acidic, and xyloglucan. Gene expression of H+-ATPase was not changed but of expansin A reduced in clinostat-treated cells. However, the gene expression and activity of xyloglucan endotransglycosylase/hydrolases (XTH; EC 2.4.1.207) and endo-(1,4)-β-D-glucanase (EGase; EC 3.2.1.4), the amount of arabinogalactan proteins (AGP), and the expression of wall-associated kinase (WAK) gene significantly increased by clinorotation. Altered gravity also reduced the activity of polyphenol oxidase and covalently bound peroxidase. The results suggest that altered gravity promoted orchestrated changes of wall-modifying genes and proteins which reduced its stiffness and enhanced cell expansion and division potential. • Clinorotation changed the polysaccharides and protein composition of the cell wall. • Substantial changes were observed in expression pattern of wall modifying genes. • Reducing wall stiffening increased cell expansion and division potential. [ABSTRACT FROM AUTHOR]

The wall-associated kinases (WAKs) can perceive and transmit extracellular signals as one kind of unique receptor-like kinases (RLKs) involved in the regulation of cell expansion, pathogen resistance and abiotic stress tolerance. To understand their potential roles and screen some key candidates in Medicago truncatula (M. truncatula), genome-wide identification and characterization of MtWAKs were conducted in this study. A total of 54 MtWAK genes were identified and classified into four groups based on their protein domains. They were distributed on all chromosomes, while most of them were clustered on chromosome 1 and 3. The synteny analysis showed that 11 orthologous pairs were identified between M. truncatula and Arabidopsis thaliana (A. thaliana) and 31 pairs between M. truncatula and Glycine max (G. max). The phylogenetic analysis showed that WAK-RLKs were classified into five clades, and they exhibited a species-specific expansion. Most MtWAK-RLKs had similar exon–intron organization and motif distribution. Multiple cis-acting elements responsive to phytohormones, stresses, growth and development were observed in the promoter regions of MtWAK-RLKs. In addition, the expression patterns of MtWAK-RLKs varied with different plant tissues, developmental stages and biotic and abiotic stresses. Interestingly, plasm membrane localized MtWAK24 significantly inhibited Phytophthora infection in tobacco. The study provides valuable information for characterizing the molecular functions of MtWAKs in regulation of plant growth, development and stress tolerance in legume plants.

Background: Wall-associated kinase (WAK)/WAK-like (WAKL) is one of the subfamily of receptor like kinases (RLK). Although previous studies reported that WAK/WAKL played an important role in plant cell elongation, response to biotic and abiotic stresses, there are no systematic studies on RcWAK/RcWAKL in rose. Results: In this study, we identified a total of 68 RcWAK/RcWAKL gene family members within rose (Rosa chinensis) genome. The RcWAKs contained the extracellular galacturonan-binding domain and calcium-binding epidermal growth factor (EGF)-like domain, as well as an intracellular kinase domains. The RcWAKLs are missing either calcium-binding EGF-like domain or the galacturonan-binding domain in their extracellular region. The phylogenetic analysis showed the RcWAK/RcWAKL gene family has been divided into five groups, and these RcWAK/RcWAKL genes were unevenly distributed on the 7 chromosomes of rose. 12 of RcWAK/RcWAKL genes were significantly up-regulated by Botrytis cinerea-inoculated rose petals, where RcWAK4 was the most strongly expressed. Virus induced gene silencing of RcWAK4 increased the rose petal sensitivity to B. cinerea. The results indicated RcWAK4 is involved in the resistance of rose petal against B. cinerea. Conclusion: Our study provides useful information to further investigate the function of the RcWAK/RcWAKL gene family and breeding research for resistance to B. cinerea in rose. [ABSTRACT FROM AUTHOR]

Background: Verticillium wilt, caused by the soil borne fungus Verticillium dahliae, is a major threat to cotton production worldwide. An increasing number of findings indicate that WAK genes participate in plant−pathogen interactions, but their roles in cotton resistance to V. dahliae remain largely unclear. Results: Here, we carried out a genome-wide analysis of WAK gene family in Gossypium hirsutum that resulted in the identification of 81 putative GhWAKs, which were all predicated to be localized on plasma membrane. In which, GhWAK77 as a representative was further located in tobacco epidermal cells using transient expression of fluorescent fusion proteins. All GhWAKs could be classified into seven groups according to their diverse protein domains, indicating that they might sense different outside signals to trigger intracellular signaling pathways that were response to various environmental stresses. A lot of cis-regulatory elements were predicted in the upstream region of GhWAKs and classified into four main groups including hormones, biotic, abiotic and light. As many as 28 GhWAKs, playing a potential role in the interaction between cotton and V. dahliae, were screened out by RNA-seq and qRT-PCR. To further study the function of GhWAKs in cotton resistance to V. dahliae, VIGS technology was used to silence GhWAKs. At 20 dpi, VIGSed plants exhibited more chlorosis and wilting than the control plants. The disease indices of VIGSed plants were also significantly higher than those of the control. Furthermore, silencing of GhWAKs significantly affected the expression of JA- and SA-related marker genes, increased the spread of V. dahliae in the cotton stems, dramatically compromised V. dahliae-induced accumulation of lignin, H2O2 and NO, but enhanced POD activity. Conclusion: Our study presents a comprehensive analysis on cotton WAK gene family for the first time. Expression analysis and VIGS assay provided direct evidences on GhWAKs participation in the cotton resistance to V. dahliae. [ABSTRACT FROM AUTHOR]

Red rot disease is a severe disease of sugarcane that affects the crop productivity in sugarcane growing countries. In this study, resistance gene analogues (RGAs) similar to kinase resistance protein isolated from sugarcane red rot resistant, moderately resistant and susceptible genotypes were compared with wall associated receptor like kinases of various plants. The non-RD serine/threonine kinase regions were noticed in all identified sugarcane RGAs. The amino acid identity percentage among resistant, moderately resistant and susceptible sugarcane RGAs was more than 90% which indicated that conserved kinase region is present in these RGAs. However, when compared with other monocots and dicots, the identified RGAs showed much diversity in kinase region. As the RGAs of sugarcane are of non-RD serine/threonine kinase that are typically associated with immune responses in plant, the findings may be extremely useful that can be used as RGAs based marker development for resistance breeding in sugarcane. [ABSTRACT FROM AUTHOR]

Wall-associated kinases (WAKs) are a family of receptor-like kinases (RLKs) with important roles against biotic and abiotic stresses in plants. Here, we reported that a rice WAK gene, OsWAK11 , detoxifies excess copper by regulating the methylesterification of the cell wall. RNA interference- (RNAi-) mediated OsWAK11 knockdown in rice resulted in hypersensitivity to copper toxicity. This Cu hypersensitivity in OsWAK11 -RNAi transgenic lines might result from more Cu uptake, which accumulated in the cytoplasm rather than the cell wall. Surprisingly, less Cu was accumulated in the cell wall pectin and hemicellulose of OsWAK11 -RNAi transgenic lines than in wild-type plants, possibly because of decreased pectin methylesterase (PME) activity. We detected dramatically reduced expression of a key PME encoding gene, OsPME14 , in OsWAK11 -RNAi plants. Furthermore, disruption of OsPME14 expression could mimic the effects of OsWAK11 downregulation in plants challenged by excess Cu. Given that OsWAK11 expression is induced by excess Cu, our results indicate that plant cells activate OsWAK11 activity to modify the properties of the cell wall, thereby retaining Cu on the wall when subjected to excess Cu. [ABSTRACT FROM AUTHOR]

We aimed to investigate abiotic stress (WAK, HvPIP1.1, HvPIP1.2, HvPIP1.3, HvPIP1.5, CYCD3, DREB2) and brassinosteroid-related gene (DWARF4) expressions in barley (Hordeum vulgare L. cv. “Hilal”) roots grown under different salt (150 and 250 mM), HBR (0.5 and 1 μM), and salt + HBR applications during 48 and 72 h at dark with their controls. Phylogenetic trees were also constructed to observe relationships among genes found in other plants. The expression of HvPIP1.2 and WAK reduced after salt treatment while HvPIP1.3, DREB2 and DWARF4 expressions increased. HvPIP1.1, HvPIP1.2, HvPIP1.3, HvPIP1.5 and DWARF4 expressions were upregulated under only HBR applications. Salt + HBR treatments increased HvPIP1.1, DREB2 and DWARF4 but decreased HvPIP1.2. Phylogenetic analyses indicated that Oryza sativa L. shared similar sequences with HvPIP1.5. CYCD3 could diverge relatively earlier from cyclin genes during evolution as it segregates in a distinct clade. Sorghum bicolor showed sequence homology with DREB2. Oryza australiensis L. and DWARF4 were found in the same clade. To our knowledge, this is the first detailed report related to salt stress and HBR applications in terms of the expression of different genes in barley, providing a valuable information for molecular breeding improvement of stress-related traits. [ABSTRACT FROM AUTHOR]

Disease has an effect on crop yields, causing significant losses. As the worldwide demand for agricultural products increases, there is a need to pursue the development of new methods to protect crops from disease. One mechanism of plant protection is through the activation of the plant immune system. By exogenous application, 'plant activator molecules' with elicitor properties can be used to activate the plant immune system. These defence-inducing molecules represent a powerful and often environmentally friendly tool to fight pathogens. We show that the secondary bile acid deoxycholic acid (DCA) induces defence in Arabidopsis and reduces the proliferation of two bacterial phytopathogens: Erwinia amylovora and Pseudomonas syringae pv. tomato. We describe the global defence response triggered by this new plant activator in Arabidopsis at the transcriptional level. Several induced genes were selected for further analysis by quantitative reverse transcription-polymerase chain reaction. We describe the kinetics of their induction and show that abiotic stress, such as moderate drought or nitrogen limitation, does not impede DCA induction of defence. Finally, we investigate the role in the activation of defence by this bile acid of the salicylic acid biosynthesis gene SID2, of the receptor-like kinase family genes WAK1-3 and of the NADPH oxidase-encoding RbohD gene. Altogether, we show that DCA constitutes a promising molecule for plant protection which can induce complementary lines of defence, such as callose deposition, reactive oxygen species accumulation and the jasmonic acid and salicylic acid signalling pathways. [ABSTRACT FROM AUTHOR]

The environment is a dynamic system in which life forms adapt. Wall-Associated Kinases ( WAK ) are a subfamily of receptor-like kinases associated with the cell wall. These genes have been suggested as sensors of the extracellular environment and triggers of intracellular signals. They belong to the ePK superfamily with or without a conserved arginine before the catalytic subdomain VIB, which characterizes RD and non-RD WAKs . WAK is a large subfamily in rice. We performed an extensive comparison of WAK genes from A. thaliana ( AtWAK ), O. sativa japonica and indica subspecies ( OsWAK ). Phylogenetic studies and WAK domain characterization allowed for the identification of two distinct groups of WAK genes in Arabidopsis and rice. One group corresponds to a cluster containing only OsWAKs that most likely expanded after the monocot–dicot separation, which evolved into a non-RD kinase class. The other group comprises classical RD-kinases with both AtWAK and OsWAK representatives. Clusterization analysis using extracellular and kinase domains demonstrated putative functional redundancy for some genes, but also highlighted genes that could recognize similar extracellular stimuli and activate different cascades. The gene expression pattern of WAKs in response to cold suggests differences in the regulation of the OsWAK genes in the indica and japonica subspecies. Our results also confirm the hypothesis of functional diversification between A. thaliana and O. sativa WAK genes. Furthermore, we propose that plant WAK s constitute two evolutionarily related but independent subfamilies: WAK -RD and WAK -nonRD. Recognition of this structural division will further provide insights to understanding WAK functions and regulations. [ABSTRACT FROM AUTHOR]

The wall-associated kinases (WAKs) are a family of transmembrane proteins involved in pathogen responses and cell elongation in Arabidopsis. They belong to the major receptor-like kinase (RLK) family in plants. Given their architecture and connection to the cell wall, WAKs are thought to perceive and propagate extracellular signals. This study reports the characterization of the WAK family in a woody species based on the v3.0 genome assembly of Populus trichocarpa. In silico analysis revealed a total of 175 PtWAK sequences classified into four groups based on protein domains. Of the PtWAKs, 91.5 % were found in tandem-duplicated clusters contributing to the expansion of the family in poplar. Microarray and EST expression data mining revealed contrasting temporal and spatial expression patterns in stress treatments for several WAK members. The WAKs in poplar form the largest WAK family encountered to date in plants. The combination of phylogenetic and transcriptional data showed that members in nonexpanded clusters were mainly expressed in developmental processes, whereas PtWAKs that had evolved independently in a species-specific way were structured in clusters and were involved in resistance responses. This paper offers an overview of WAK family structure in P. trichocarpa, which will be useful for further functional analysis of the PtWAK family. [ABSTRACT FROM AUTHOR]

The Wall-Associated Kinase, one of the receptor-like kinase (RLK) gene families in plant, plays important roles in cell expansion, pathogen resistance and heavy metal stress tolerance in Arabidopsis thaliana. Here, we isolated a cDNA encoding a novel WAK from indica rice and designated as OsiWAK1 ( Oryza sativa indica WAK-1). In this study, the RNAi construct with OsiWAK1 gene cloned in sense and antisense orientation separated by a functional intron under constitutive promoter, was introduced through biolistic gene gun method into the rice cultivar 'IR-50' to determine the effect of OsiWAK1 transcript silencing on rice plant development. Examination of the transgenic plants reveals that OsiWAK1 transcript silencing in rice results in dwarf plants because of the reduction in the size of leaves, flag-leaves, internodes and panicle. The development of root primordia during germination, root hairs and lateral rooting was also effected. Microscopic analysis revealed that the decrease in size is due to reduction in the cell size but not the number of cells. In addition, the transgenic plants also exhibited sterile phenotype due to anther indehiscence and 40 % reduction in pollen viability. These data suggest that OsiWAK1 may play an important role in rice plant growth and development. [ABSTRACT FROM AUTHOR]

Abstract: The reported results demonstrate that Orobanche ramosa exudates, released over seed germination, are involved in the early tomato perception of this pathogen. For the first time, a 2642 bp cDNA displaying characteristic features of wall-associated kinase receptor was cloned and characterized in tomato. Expression studies revealed that transcript level of this Lycopersicon esculentum wall-associated kinase (LeWAK) increased early in tomato roots and in cell suspensions challenged with Orobanche ramosa. The involvement of LeWAK as a sensor of cell wall alterations during broomrape attack and the subsequent activation of defense reactions is discussed in this paper. [Copyright &y& Elsevier]

There are only a few proteins identified at the cell surface that could directly regulate plant cell wall functions. The cell wall-associated kinases (WAKs) of angiosperms physically link the plasma membrane to the carbohydrate matrix and are unique in that they have the potential to directly signal cellular events through their cytoplasmic kinase domain. In Arabidopsis there are five WAKs and each has a cytoplasmic serine/threonine protein kinase domain, spans the plasma membrane, and extends a domain into the cell wall. The WAK extracellular domain is variable among the five isoforms, and collectively the family is expressed in most vegetative tissues. WAK1 and WAK2 are the most ubiquitously and abundantly expressed of the five tandemly arrayed genes, and their messages are present in vegetative meristems, junctions of organ types, and areas of cell expansion. They are also induced by pathogen infection and wounding. Recent experiments demonstrate that antisense WAK expression leads to a reduction in WAK protein levels and the loss of cell expansion. A large amount of WAK is covalently linked to pectin, and most WAK that is bound to pectin is also phosphorylated. In addition, one WAK isoform binds to a secreted glycine-rich protein (GRP). The data support a model where WAK is bound to GRP as a phosphorylated kinase, and also binds to pectin. How WAKs are involved in signaling from the pectin extracellular matrix in coordination with GRPs will be key to our understanding of the cell wall's role in cell growth. [ABSTRACT FROM AUTHOR]