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Arabidopsis mlo3 mutant plants exhibit spontaneous callose deposition and signs of early leaf senescence

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Arabidopsis thaliana mlo3 mutant plants are not affected in pathogen infection phenotypes but—reminiscent of mlo2 mutant plants—exhibit spontaneous callose deposition and signs of early leaf senescence.

Abstract

The family of Mildew resistance Locus O (MLO) proteins is best known for its profound effect on the outcome of powdery mildew infections: when the appropriate MLO protein is absent, the plant is fully resistant to otherwise virulent powdery mildew fungi. However, most members of the MLO protein family remain functionally unexplored. Here, we investigate Arabidopsis thaliana MLO3, the closest relative of AtMLO2, AtMLO6 and AtMLO12, which are the Arabidopsis MLO genes implicated in the powdery mildew interaction. The co-expression network of AtMLO3 suggests association of the gene with plant defense-related processes such as salicylic acid homeostasis. Our extensive analysis shows that mlo3 mutants are unaffected regarding their infection phenotype upon challenge with the powdery mildew fungi Golovinomyces orontii and Erysiphe pisi, the oomycete Hyaloperonospora arabidopsidis, and the bacterial pathogen Pseudomonas syringae (the latter both in terms of basal and systemic acquired resistance), indicating that the protein does not play a major role in the response to any of these pathogens. However, mlo3 genotypes display spontaneous callose deposition as well as signs of early senescence in 6- or 7-week-old rosette leaves in the absence of any pathogen challenge, a phenotype that is reminiscent of mlo2 mutant plants. We hypothesize that de-regulated callose deposition in mlo3 genotypes might be the result of a subtle transient aberration of salicylic acid-jasmonic acid homeostasis during development.

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Abbreviations

bp:

Base pair

CFU:

Colony forming units

dpi:

Days post inoculation

FW:

Fresh weight

GO:

Gene ontology

GUS:

β-glucuronidase

Hpa :

Hyaloperonospra arabidopsidis

hpi:

Hours post inoculation

JA:

Jasmonic acid

JA-Ile:

Jasmonic acid isoleucine

MAMP:

Microbe-associated molecular pattern

MS:

Murashige and Skoog

Psm :

Pseudomonas syringae pv. maculicola

Pst :

Pseudomonas syringae pv. tomato

RH:

Relative humidity

rpm:

rounds per minute

RLU:

Relative light units

RT-PCR:

Reverse transcriptase polymerase chain reaction

SA:

Salicylic acid

SAG:

Salicylic acid glucoside

SAR:

Systemic acquired resistance

T-DNA:

Transfer-DNA

UPLC-nano ESI–MS/MS:

Ultrahigh-pressure liquid chromatography-tandem mass spectrometry

YFP:

Yellow fluorescent protein

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Acknowledgements

This study was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft; DFG) [Grant PA861/11-1 to R.P. and Grant INST 186/822-1 to I.F.]. H. arabidopsidis Noco2 was kindly provided by Jane Parker (Max Planck Institute for Plant Breeding Research, Cologne, Germany). The two P. syringae pv. maculicola strains were kindly provided by Jürgen Zeier (Heinrich Heine University, Düsseldorf, Germany). This work would not have been possible without coffee and chocolate.

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Authors and Affiliations

Authors

Contributions

S.K. and S.T. performed the pathogen assays, K.G. did the SAR experiments. S.K. and A.R. conducted callose, senescence, GUS and osmotic stress assays. Phytohormone measurements were performed by K.Z., and K.Z. and I.F. analyzed the data. S.K. did the expression analysis, statistical testing, and plotting of the data. R.P. and S.K. designed the project and wrote the manuscript. All authors have read and approved the manuscript.

Corresponding author

Correspondence to Ralph Panstruga.

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The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Supplementary material 1 (PDF 681 kb)

Supplementary material 2 (PDF 345 kb)

Supplementary material 3 (PDF 225 kb)

Supplementary material 4 (PDF 233 kb)

Supplementary material 5 (PDF 237 kb)

Supplementary material 6 (PDF 259 kb)

Supplementary material 7 (PDF 249 kb)

Supplementary material 8 (PDF 251 kb)

Supplementary material 9 (DOCX 29 kb)

11103_2019_877_MOESM10_ESM.xlsx

Supplementary material 10—Co-expressed genes of AtMLO1, AtMLO2, and AtMLO3 after ATTED-II release v2017.12.14 (XLSX 202 kb)

11103_2019_877_MOESM11_ESM.txt

Supplementary material 11—GO terms of the 79 genes from the common co-expression network of AtMLO2 and AtMLO3 (TXT 66 kb)

11103_2019_877_MOESM12_ESM.xlsx

Supplementary material 12—Cis-regulatory elements of the 79 genes from the common co-expression network of AtMLO2 and AtMLO3 predicted by AthaMap (XLSX 240 kb)

11103_2019_877_MOESM13_ESM.xlsx

Supplementary material 13—Cis-regulatory elements of the 79 genes from the common co-expression network of AtMLO2 and AtMLO3 predicted by MEME v5.0.4 (XLSX 41 kb)

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Kusch, S., Thiery, S., Reinstädler, A. et al. Arabidopsis mlo3 mutant plants exhibit spontaneous callose deposition and signs of early leaf senescence. Plant Mol Biol 101, 21–40 (2019). https://doi.org/10.1007/s11103-019-00877-z

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  • DOI: https://doi.org/10.1007/s11103-019-00877-z

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