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Title: STAYGREEN (CsSGR) is a candidate for the anthracnose (Colletotrichum orbiculare) resistance locus cla in Gy14 cucumber

Author
item PAN, JUNSONG - University Of Wisconsin
item TAN, JUNYI - University Of Wisconsin
item WANG, YUHUI - University Of Wisconsin
item ZHENG, XIANGYANG - Harris Moran Seed Company
item OWENS, KEN - Harris Moran Seed Company
item LI, DAWEI - University Of Wisconsin
item LI, YUHONG - University Of Wisconsin
item Weng, Yiqun

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2018
Publication Date: 4/21/2018
Citation: Pan, J., Tan, J., Wang, Y., Zheng, X., Owens, K., Li, D., Li, Y., Weng, Y. 2018. STAYGREEN (CsSGR) is a candidate for the anthracnose (Colletotrichum orbiculare) resistance locus cla in Gy14 cucumber. Journal of Theoretical and Applied Genetics. 131(7):1577-1587. https://doi.org/10.1007/s00122-018-3099-1.
DOI: https://doi.org/10.1007/s00122-018-3099-1

Interpretive Summary: The anthracnose is an important fungal pathogen in cucumber and other cucurbit crops. No host resistance genes against this disease have been cloned in crop plants. Here we reported fine mapping and cloning of a resistance gene to the race 1 anthracnose pathogen in cucumber inbred lines Gy14 and WI 2757. Genetic analysis revealed a single recessive gene, cla, was responsible for anthracnose resistance in both lines, but WI2757 carries an additional minor-effect QTL. Fine genetic mapping identified a 32 kb region harboring the resistance gene in cucumber Chromosome 5 with three predicted genes. Multiple lines of evidence suggested the cucumber STAYGREEN (CsSGR) gene is a candidate for the anthracnose resistance. A single nucleotide mutation in the third exon of CsSGR resulted in the substitution of Glutamine in 9930 to Arginine in Gy14 in CsSGR protein which seems responsible for the differential anthracnose inoculation responses between Gy14 and 9930. Expression of CsSGR was significantly increased upon anthracnose pathogen inoculation in the susceptible cucumber line 9930, while its expression was much lower in the resistant Gy14. Investigation in natural cucumber populations revealed that the resistance allele in almost all improved cultivars or breeding lines of the U.S. origin was derived from PI 197087. This work reveals an unknown function for the highly conserved STAYGREEN (SGR) family genes for host disease resistance in plants.

Technical Abstract: Colletotrichum orbiculare is a hemibiotrophic fungal pathogen that causes anthracnose disease in cucumber and other cucurbit crops. No host resistance genes against the anthracnose pathogens have been cloned in crop plants. Here we reported fine mapping and cloning of a resistance gene to the race 1 anthracnose pathogen in cucumber inbred lines Gy14 and WI 2757. Phenotypic and QTL analysis in multiple populations revealed a single recessive gene, cla, was underlying anthracnose resistance in both lines, but WI2757 carried an additional minor-effect QTL. Fine mapping using 150 Gy14 × 9930 recombinant inbred lines and 1,043 F2 individuals delimited the cla locus into a 32 kb region in cucumber Chromosome 5 with three predicted genes. Multiple lines of evidence suggested the cucumber STAYGREEN (CsSGR) gene is a candidate for the anthracnose resistance locus. A single nucleotide mutation in the third exon of CsSGR resulted in the substitution of Glutamine in 9930 to Arginine in Gy14 in CsSGR protein which seems responsible for the differential anthracnose inoculation responses between Gy14 and 9930. Quantitative real-time PCR analysis indicated that CsSGR was significantly upregulated upon anthracnose pathogen inoculation in the susceptible 9930, while its expression was much lower in the resistant Gy14. Investigation of allelic diversities in natural cucumber populations revealed that the resistance allele in almost all improved cultivars or breeding lines of the U.S. origin was derived from PI 197087. This work reveals an unknown function for the highly conserved STAYGREEN (SGR) family genes for host disease resistance in plants.