Abstract
G protein-coupled receptors (GPCRs) are a large transmembrane receptor superfamily that is involved in many cellular signaling pathways. In the present study, GPCR-family genes from the toxigenic and necrotrophic plant pathogen Alternaria alternata were cloned and characterized. Three GPCR-encoding genes, AaGPR1, AaGPR2, and AaGPR3 were identified in the draft genomic data of the A. alternata tomato pathotype, which produces the host-specific AAL-toxin. AaGPR1, AaGPR2, and AaGPR3 each encodes a protein containing a seven transmembrane domain that is characteristic of GPCRs. Targeted deletion of AaGPR1, AaGPR2, or AaGPR3 in the A. alternata tomato pathotype was conducted to understand the influence of G-protein signaling mechanisms on developmental processes and virulence of this pathogen. No changes in colony morphology or AAL-toxin production were observed for the deletion strain ΔAaGPR1, 2, and 3, compared with the wild-type strain. However, one deletion strain, ΔAaGPR3, exhibited aberrant conidial morphology including decreased conidial length and beak formation. The ability to induce the formation of necrotic lesions on susceptible leaves also significantly decreased in ΔAaGPR3, indicating a reduction in virulence. These defects are similar to the phenotypes found for the Gα gene (AGA1) mutant of A. alternata. These results indicate that the G-protein signal transduction pathway appears to be involved in conidial development and virulence of A. alternata.
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Acknowledgments
We thank R. P. Oliver for providing pAN7-1. We are grateful to J. Hille, B. F. Brandwagt, D. G. Gilchrist, K. Akimitsu, and T. L. Peever for providing Alternaria strains. This work was supported by Grant-in-Aid for JSPS Fellows (Grant 24 8246), and Grant-in-Aid for Scientific Research (S) (19108001), (A) (23248007), (B) (23380025) and (B) (26304025) from the Japanese Society for Promotion of Sciences, and Global COE Program “Advanced Utilization of Fungus/Mushroom Resources for Sustainable Society in Harmony with Nature” by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan.
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10327_2016_647_MOESM2_ESM.tiff
Supplementary Fig. 1. Membrane topology of predicted proteins from AaGPR1, AaGPR2, and AaGPR3. Seven possible transmembrane domains of typical GPCR proteins were predicted by the SOSUI program. (TIFF 2702 kb)
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Takao, K., Akagi, Y., Tsuge, T. et al. Functional characterization of putative G protein-coupled receptors in the tomato pathotype of Alternaria alternata . J Gen Plant Pathol 82, 82–88 (2016). https://doi.org/10.1007/s10327-016-0647-x
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DOI: https://doi.org/10.1007/s10327-016-0647-x