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The kinase LYK5 is a major chitin receptor in Arabidopsis and forms a chitin-induced complex with related kinase CERK1.

Cao Y, Liang Y, Tanaka K, Nguyen CT, Jedrzejczak RP, Joachimiak A, Stacey G - Elife (2014)

Bottom Line: Chitin is a fungal microbe-associated molecular pattern recognized in Arabidopsis by a lysin motif receptor kinase (LYK), AtCERK1.Mutations in AtLYK5 resulted in a significant reduction in chitin response.The data suggest that AtLYK5 is the primary receptor for chitin, forming a chitin inducible complex with AtCERK1 to induce plant immunity.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant Sciences, National Center for Soybean Biotechnology, University of Missouri, Columbia, United States.

ABSTRACT
Chitin is a fungal microbe-associated molecular pattern recognized in Arabidopsis by a lysin motif receptor kinase (LYK), AtCERK1. Previous research suggested that AtCERK1 is the major chitin receptor and mediates chitin-induced signaling through homodimerization and phosphorylation. However, the reported chitin binding affinity of AtCERK1 is quite low, suggesting another receptor with high chitin binding affinity might be present. Here, we propose that AtLYK5 is the primary chitin receptor in Arabidopsis. Mutations in AtLYK5 resulted in a significant reduction in chitin response. However, AtLYK5 shares overlapping function with AtLYK4 and, therefore, Atlyk4/Atlyk5-2 double mutants show a complete loss of chitin response. AtLYK5 interacts with AtCERK1 in a chitin-dependent manner. Chitin binding to AtLYK5 is indispensable for chitin-induced AtCERK1 phosphorylation. AtLYK5 binds chitin at a much higher affinity than AtCERK1. The data suggest that AtLYK5 is the primary receptor for chitin, forming a chitin inducible complex with AtCERK1 to induce plant immunity.

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Characterization of Atlyk5 mutant plants.(A) Genomic structure of AtLYK5 and two insertion sites of two mutants. (B) Identification of T-DNA insertion by PCR using genomic DNA from Col-0 wild-type and Atlyk5-2 mutant plants. Location of primers used is shown in (A). Primer sequences are listed in Supplemental file 1. (C) RT-PCR was used to identify transcriptional expression of AtLYK5 in Col-0 WT and Atlyk5-2 mutant plants. Upper panel shows expression level of AtLYK5 in Col-0 and Atlyk5-2 mutant plants, lower panel shows expression of AtCERK1 as a control.DOI:http://dx.doi.org/10.7554/eLife.03766.007
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fig1s3: Characterization of Atlyk5 mutant plants.(A) Genomic structure of AtLYK5 and two insertion sites of two mutants. (B) Identification of T-DNA insertion by PCR using genomic DNA from Col-0 wild-type and Atlyk5-2 mutant plants. Location of primers used is shown in (A). Primer sequences are listed in Supplemental file 1. (C) RT-PCR was used to identify transcriptional expression of AtLYK5 in Col-0 WT and Atlyk5-2 mutant plants. Upper panel shows expression level of AtLYK5 in Col-0 and Atlyk5-2 mutant plants, lower panel shows expression of AtCERK1 as a control.DOI:http://dx.doi.org/10.7554/eLife.03766.007

Mentions: Given these concerns, we identified and characterized a Col-0 Atlyk5 mutant (Atlyk5-2) from the SALK population (Figure 1—figure supplement 3). This line has a T-DNA in the extracellular domain of AtLYK5 (Figure 1—figure supplement 3). It should be noted that in our original publications (Wan et al., 2008, 2012), all of the Atlyk mutants, with the exception of Atlyk5-1, were derived from the Col-0 ecotype. As shown in Figure 1A, chitin-induced ROS production was significantly lower in the Atlyk5-2 mutant plants compared to Col-O wild-type plants (Figure 1A). Calcium influx is activated by exposure of wild-type plants to chitin. Similar treatment of Atlyk5-2 mutant plants showed a 90% reduction and a significant delay in the calcium response, while Atcerk1 mutant plants showed essentially no calcium response to chitin (Figure 1B). Flagellin-triggered calcium influx in both Atcerk1 and Atlyk5-2 mutant plants were similar to Col-0 wild-type plants (Figure 1—figure supplement 4), indicating that these defects were specific to chitin and not to a general effect on MTI. MPK3 and MPK6 are specifically phosphorylated upon chitin elicitation in Col-0 wild-type but not in Atcerk1 mutant plants. Significant reduction in MPK phosphorylation was detected in Atlyk5-2 mutant plants after chitin treatment (Figure 1C). Consistent with these findings, the Atlyk5-2 mutant plants showed an intermediate response with regard to chitin-induced AtWRKY29, AtWRKY30, AtWRKY33, and AtWRKY53 expression compared to the Col-0 wild-type and the Atcerk1 mutant plants (Figure 1D,E, Figure 1—figure supplement 4). Both Atcerk1 and Atlyk5-2 mutant plants showed increased susceptibility to the fungal pathogen Alternaria brassicicola compared with Col-0 wild-type plants. Pretreatment with chitooctaose enhanced resistance to A. brassicicola in wild-type plants but not in Atcerk1 or Atlyk5-2 mutant plants (Figure 1F). Untreated Atcerk1 and Atlyk5-2 mutant plants showed wild-type levels of resistance to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. However, only the wild-type showed increased bacterial resistance when plants were pretreated with chitooctaose to induce MTI (Figure 1G). In order to confirm that the loss of chitin response was due to the AtLYK5 mutation, transgenic plants expressing the full-length AtLYK5 gene were generated under control of its native promoter in the Atlyk5-2 mutant genetic background (Figure 2—figure supplement 1). Expression of AtLYK5 in Atlyk5-2 mutant plants complemented all of the chitin-induced responses, including ROS production and MAPK phosphorylation (Figure 2—figure supplement 1). These data indicate that AtLYK5 is essential for a strong response to chitin elicitation. The response of all five Atlyk mutant plants was tested based on chitin-induced ROS prodction (Figure 1—figure supplement 5), confirming that AtCERK1, AtLYK4 and AtLYK5, but not AtLYK2 or AtLYK3 are involved in chitin signaling.10.7554/eLife.03766.003Figure 1.Atlyk5 mutant plants are defective in chitin-triggered immune responses.


The kinase LYK5 is a major chitin receptor in Arabidopsis and forms a chitin-induced complex with related kinase CERK1.

Cao Y, Liang Y, Tanaka K, Nguyen CT, Jedrzejczak RP, Joachimiak A, Stacey G - Elife (2014)

Characterization of Atlyk5 mutant plants.(A) Genomic structure of AtLYK5 and two insertion sites of two mutants. (B) Identification of T-DNA insertion by PCR using genomic DNA from Col-0 wild-type and Atlyk5-2 mutant plants. Location of primers used is shown in (A). Primer sequences are listed in Supplemental file 1. (C) RT-PCR was used to identify transcriptional expression of AtLYK5 in Col-0 WT and Atlyk5-2 mutant plants. Upper panel shows expression level of AtLYK5 in Col-0 and Atlyk5-2 mutant plants, lower panel shows expression of AtCERK1 as a control.DOI:http://dx.doi.org/10.7554/eLife.03766.007
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fig1s3: Characterization of Atlyk5 mutant plants.(A) Genomic structure of AtLYK5 and two insertion sites of two mutants. (B) Identification of T-DNA insertion by PCR using genomic DNA from Col-0 wild-type and Atlyk5-2 mutant plants. Location of primers used is shown in (A). Primer sequences are listed in Supplemental file 1. (C) RT-PCR was used to identify transcriptional expression of AtLYK5 in Col-0 WT and Atlyk5-2 mutant plants. Upper panel shows expression level of AtLYK5 in Col-0 and Atlyk5-2 mutant plants, lower panel shows expression of AtCERK1 as a control.DOI:http://dx.doi.org/10.7554/eLife.03766.007
Mentions: Given these concerns, we identified and characterized a Col-0 Atlyk5 mutant (Atlyk5-2) from the SALK population (Figure 1—figure supplement 3). This line has a T-DNA in the extracellular domain of AtLYK5 (Figure 1—figure supplement 3). It should be noted that in our original publications (Wan et al., 2008, 2012), all of the Atlyk mutants, with the exception of Atlyk5-1, were derived from the Col-0 ecotype. As shown in Figure 1A, chitin-induced ROS production was significantly lower in the Atlyk5-2 mutant plants compared to Col-O wild-type plants (Figure 1A). Calcium influx is activated by exposure of wild-type plants to chitin. Similar treatment of Atlyk5-2 mutant plants showed a 90% reduction and a significant delay in the calcium response, while Atcerk1 mutant plants showed essentially no calcium response to chitin (Figure 1B). Flagellin-triggered calcium influx in both Atcerk1 and Atlyk5-2 mutant plants were similar to Col-0 wild-type plants (Figure 1—figure supplement 4), indicating that these defects were specific to chitin and not to a general effect on MTI. MPK3 and MPK6 are specifically phosphorylated upon chitin elicitation in Col-0 wild-type but not in Atcerk1 mutant plants. Significant reduction in MPK phosphorylation was detected in Atlyk5-2 mutant plants after chitin treatment (Figure 1C). Consistent with these findings, the Atlyk5-2 mutant plants showed an intermediate response with regard to chitin-induced AtWRKY29, AtWRKY30, AtWRKY33, and AtWRKY53 expression compared to the Col-0 wild-type and the Atcerk1 mutant plants (Figure 1D,E, Figure 1—figure supplement 4). Both Atcerk1 and Atlyk5-2 mutant plants showed increased susceptibility to the fungal pathogen Alternaria brassicicola compared with Col-0 wild-type plants. Pretreatment with chitooctaose enhanced resistance to A. brassicicola in wild-type plants but not in Atcerk1 or Atlyk5-2 mutant plants (Figure 1F). Untreated Atcerk1 and Atlyk5-2 mutant plants showed wild-type levels of resistance to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. However, only the wild-type showed increased bacterial resistance when plants were pretreated with chitooctaose to induce MTI (Figure 1G). In order to confirm that the loss of chitin response was due to the AtLYK5 mutation, transgenic plants expressing the full-length AtLYK5 gene were generated under control of its native promoter in the Atlyk5-2 mutant genetic background (Figure 2—figure supplement 1). Expression of AtLYK5 in Atlyk5-2 mutant plants complemented all of the chitin-induced responses, including ROS production and MAPK phosphorylation (Figure 2—figure supplement 1). These data indicate that AtLYK5 is essential for a strong response to chitin elicitation. The response of all five Atlyk mutant plants was tested based on chitin-induced ROS prodction (Figure 1—figure supplement 5), confirming that AtCERK1, AtLYK4 and AtLYK5, but not AtLYK2 or AtLYK3 are involved in chitin signaling.10.7554/eLife.03766.003Figure 1.Atlyk5 mutant plants are defective in chitin-triggered immune responses.

Bottom Line: Chitin is a fungal microbe-associated molecular pattern recognized in Arabidopsis by a lysin motif receptor kinase (LYK), AtCERK1.Mutations in AtLYK5 resulted in a significant reduction in chitin response.The data suggest that AtLYK5 is the primary receptor for chitin, forming a chitin inducible complex with AtCERK1 to induce plant immunity.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant Sciences, National Center for Soybean Biotechnology, University of Missouri, Columbia, United States.

ABSTRACT
Chitin is a fungal microbe-associated molecular pattern recognized in Arabidopsis by a lysin motif receptor kinase (LYK), AtCERK1. Previous research suggested that AtCERK1 is the major chitin receptor and mediates chitin-induced signaling through homodimerization and phosphorylation. However, the reported chitin binding affinity of AtCERK1 is quite low, suggesting another receptor with high chitin binding affinity might be present. Here, we propose that AtLYK5 is the primary chitin receptor in Arabidopsis. Mutations in AtLYK5 resulted in a significant reduction in chitin response. However, AtLYK5 shares overlapping function with AtLYK4 and, therefore, Atlyk4/Atlyk5-2 double mutants show a complete loss of chitin response. AtLYK5 interacts with AtCERK1 in a chitin-dependent manner. Chitin binding to AtLYK5 is indispensable for chitin-induced AtCERK1 phosphorylation. AtLYK5 binds chitin at a much higher affinity than AtCERK1. The data suggest that AtLYK5 is the primary receptor for chitin, forming a chitin inducible complex with AtCERK1 to induce plant immunity.

Show MeSH