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OXI1 protein kinase is required for plant immunity against Pseudomonas syringae in Arabidopsis.

Petersen LN, Ingle RA, Knight MR, Denby KJ - J. Exp. Bot. (2009)

Bottom Line: Null oxi1 mutants are more susceptible to both virulent and avirulent strains of the biotrophic bacterial pathogen Pseudomonas syringae compared with the wild type, indicating that OXI1 positively regulates both basal resistance triggered by the recognition of pathogen-associated molecular patterns, as well as effector-triggered immunity.The induction of OXI1 after P. syringae infection spatially and temporally correlates with the oxidative burst.Furthermore, induction is reduced in atrbohD mutants and after application of DPI (an inhibitor of NADPH oxidases) suggesting that reactive oxygen species produced through NADPH oxidases drives OXI1 expression during this plant-pathogen interaction.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.

ABSTRACT
Expression of the Arabidopsis Oxidative Signal-Inducible1 (OXI1) serine/threonine protein kinase gene (At3g25250) is induced by oxidative stress. The kinase is required for root hair development and basal defence against the oomycete pathogen Hyaloperonospora parasitica, two separate H(2)O(2)-mediated processes. In this study, the role of OXI1 during pathogenesis was characterized further. Null oxi1 mutants are more susceptible to both virulent and avirulent strains of the biotrophic bacterial pathogen Pseudomonas syringae compared with the wild type, indicating that OXI1 positively regulates both basal resistance triggered by the recognition of pathogen-associated molecular patterns, as well as effector-triggered immunity. The level of OXI1 expression appears to be critical in mounting an appropriate defence response since OXI1 overexpressor lines also display increased susceptibility to biotrophic pathogens. The induction of OXI1 after P. syringae infection spatially and temporally correlates with the oxidative burst. Furthermore, induction is reduced in atrbohD mutants and after application of DPI (an inhibitor of NADPH oxidases) suggesting that reactive oxygen species produced through NADPH oxidases drives OXI1 expression during this plant-pathogen interaction.

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Overexpression of OXI1 increases susceptibility to the biotrophic pathogens P. syringae and H. parasitica. Analysis of bacterial titres in 3-week-old leaves of Ws-2, oxi1, 35S::OXI1, and 35S::OXI1-YFP plants pressure-inoculated with either 5×105 cfu ml−1 virulent Pst DC3000 (A) or avirulent Pst DC3000 avrB (B). The bars represent the mean log bacterial titre expressed as cfu cm−2 ±SEM (n=3 biological replicates, each consisting of three leaf discs per replicate plant). (C) Seven-day-old seedlings of genotypes Ws-2, oxi1, 35S::OXI1, and 35S::OXI1-YFP were sprayed with spores of the virulent H. parasitica strain Emco5 at a spore suspension of 5×104 spores ml−1. Bars represent the average sporulation of four independent samples of pooled seedlings for each genotype, 7 d post-infection ±SEM. An asterisk indicates a significant increase in pathogen growth compared to the wild type (Student's t test, P <0.05). Results shown are for one representative experiment of four.
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fig3: Overexpression of OXI1 increases susceptibility to the biotrophic pathogens P. syringae and H. parasitica. Analysis of bacterial titres in 3-week-old leaves of Ws-2, oxi1, 35S::OXI1, and 35S::OXI1-YFP plants pressure-inoculated with either 5×105 cfu ml−1 virulent Pst DC3000 (A) or avirulent Pst DC3000 avrB (B). The bars represent the mean log bacterial titre expressed as cfu cm−2 ±SEM (n=3 biological replicates, each consisting of three leaf discs per replicate plant). (C) Seven-day-old seedlings of genotypes Ws-2, oxi1, 35S::OXI1, and 35S::OXI1-YFP were sprayed with spores of the virulent H. parasitica strain Emco5 at a spore suspension of 5×104 spores ml−1. Bars represent the average sporulation of four independent samples of pooled seedlings for each genotype, 7 d post-infection ±SEM. An asterisk indicates a significant increase in pathogen growth compared to the wild type (Student's t test, P <0.05). Results shown are for one representative experiment of four.

Mentions: Having demonstrated that oxi1 mutants are more susceptible to P. syringae, it was tested whether increased expression of OXI1 could lead to enhanced resistance. Two independent overexpressor lines were generated; both drive OXI1 expression from the 35S CaMV promoter but one contains OXI1 fused to the reporter gene YFP. Both lines show increased OXI1 expression at the mRNA level (Fig. 2). Surprisingly, these overexpressor lines displayed enhanced susceptibility to both virulent and avirulent isolates of P. syringae (Fig. 3A, B). Since both overexpressor lines showed the same phenotype, the increased susceptibility was not due to the position of the transgene or as a consequence of the YFP fusion. Due to this unexpected result, and as oxi1 mutants show increased susceptibility to virulent H. parasitica (Rentel et al., 2004), the susceptibility of these overexpressing lines to the virulent H. parasitica isolate Emco5 was tested (Fig. 3C). Again, the 35S::OXI1 overexpressor showed enhanced susceptibility (as seen by increased sporulation) compared to the wild type. Sporulation in the 35S::OXI1-YFP line was highly variable, hence, although the average susceptiblity was increased, the result was not statistically significant. From these results it was concluded that modulation of OXI1 expression levels (either increased or knocked out) causes increased susceptibility to virulent and avirulent P. syringae as well as to virulent H. parasitica isolates.


OXI1 protein kinase is required for plant immunity against Pseudomonas syringae in Arabidopsis.

Petersen LN, Ingle RA, Knight MR, Denby KJ - J. Exp. Bot. (2009)

Overexpression of OXI1 increases susceptibility to the biotrophic pathogens P. syringae and H. parasitica. Analysis of bacterial titres in 3-week-old leaves of Ws-2, oxi1, 35S::OXI1, and 35S::OXI1-YFP plants pressure-inoculated with either 5×105 cfu ml−1 virulent Pst DC3000 (A) or avirulent Pst DC3000 avrB (B). The bars represent the mean log bacterial titre expressed as cfu cm−2 ±SEM (n=3 biological replicates, each consisting of three leaf discs per replicate plant). (C) Seven-day-old seedlings of genotypes Ws-2, oxi1, 35S::OXI1, and 35S::OXI1-YFP were sprayed with spores of the virulent H. parasitica strain Emco5 at a spore suspension of 5×104 spores ml−1. Bars represent the average sporulation of four independent samples of pooled seedlings for each genotype, 7 d post-infection ±SEM. An asterisk indicates a significant increase in pathogen growth compared to the wild type (Student's t test, P <0.05). Results shown are for one representative experiment of four.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2736892&req=5

fig3: Overexpression of OXI1 increases susceptibility to the biotrophic pathogens P. syringae and H. parasitica. Analysis of bacterial titres in 3-week-old leaves of Ws-2, oxi1, 35S::OXI1, and 35S::OXI1-YFP plants pressure-inoculated with either 5×105 cfu ml−1 virulent Pst DC3000 (A) or avirulent Pst DC3000 avrB (B). The bars represent the mean log bacterial titre expressed as cfu cm−2 ±SEM (n=3 biological replicates, each consisting of three leaf discs per replicate plant). (C) Seven-day-old seedlings of genotypes Ws-2, oxi1, 35S::OXI1, and 35S::OXI1-YFP were sprayed with spores of the virulent H. parasitica strain Emco5 at a spore suspension of 5×104 spores ml−1. Bars represent the average sporulation of four independent samples of pooled seedlings for each genotype, 7 d post-infection ±SEM. An asterisk indicates a significant increase in pathogen growth compared to the wild type (Student's t test, P <0.05). Results shown are for one representative experiment of four.
Mentions: Having demonstrated that oxi1 mutants are more susceptible to P. syringae, it was tested whether increased expression of OXI1 could lead to enhanced resistance. Two independent overexpressor lines were generated; both drive OXI1 expression from the 35S CaMV promoter but one contains OXI1 fused to the reporter gene YFP. Both lines show increased OXI1 expression at the mRNA level (Fig. 2). Surprisingly, these overexpressor lines displayed enhanced susceptibility to both virulent and avirulent isolates of P. syringae (Fig. 3A, B). Since both overexpressor lines showed the same phenotype, the increased susceptibility was not due to the position of the transgene or as a consequence of the YFP fusion. Due to this unexpected result, and as oxi1 mutants show increased susceptibility to virulent H. parasitica (Rentel et al., 2004), the susceptibility of these overexpressing lines to the virulent H. parasitica isolate Emco5 was tested (Fig. 3C). Again, the 35S::OXI1 overexpressor showed enhanced susceptibility (as seen by increased sporulation) compared to the wild type. Sporulation in the 35S::OXI1-YFP line was highly variable, hence, although the average susceptiblity was increased, the result was not statistically significant. From these results it was concluded that modulation of OXI1 expression levels (either increased or knocked out) causes increased susceptibility to virulent and avirulent P. syringae as well as to virulent H. parasitica isolates.

Bottom Line: Null oxi1 mutants are more susceptible to both virulent and avirulent strains of the biotrophic bacterial pathogen Pseudomonas syringae compared with the wild type, indicating that OXI1 positively regulates both basal resistance triggered by the recognition of pathogen-associated molecular patterns, as well as effector-triggered immunity.The induction of OXI1 after P. syringae infection spatially and temporally correlates with the oxidative burst.Furthermore, induction is reduced in atrbohD mutants and after application of DPI (an inhibitor of NADPH oxidases) suggesting that reactive oxygen species produced through NADPH oxidases drives OXI1 expression during this plant-pathogen interaction.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.

ABSTRACT
Expression of the Arabidopsis Oxidative Signal-Inducible1 (OXI1) serine/threonine protein kinase gene (At3g25250) is induced by oxidative stress. The kinase is required for root hair development and basal defence against the oomycete pathogen Hyaloperonospora parasitica, two separate H(2)O(2)-mediated processes. In this study, the role of OXI1 during pathogenesis was characterized further. Null oxi1 mutants are more susceptible to both virulent and avirulent strains of the biotrophic bacterial pathogen Pseudomonas syringae compared with the wild type, indicating that OXI1 positively regulates both basal resistance triggered by the recognition of pathogen-associated molecular patterns, as well as effector-triggered immunity. The level of OXI1 expression appears to be critical in mounting an appropriate defence response since OXI1 overexpressor lines also display increased susceptibility to biotrophic pathogens. The induction of OXI1 after P. syringae infection spatially and temporally correlates with the oxidative burst. Furthermore, induction is reduced in atrbohD mutants and after application of DPI (an inhibitor of NADPH oxidases) suggesting that reactive oxygen species produced through NADPH oxidases drives OXI1 expression during this plant-pathogen interaction.

Show MeSH
Related in: MedlinePlus