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Title: A novel allele of monoecious (m) locus is responsible for elongated fruit shape and perfect flowers in cucumber (Cucumis sativus L.)

Author
item TAN, J - Northwest Agricultural & Forestry University
item TAO, Q - Northwest Agricultural & Forestry University
item NIU, H - Northwest Agricultural & Forestry University
item ZHANG, Z - Northwest Agricultural & Forestry University
item LI, D - Heilongjiang Bayi Agricultural University (HLAU)
item GONG, Z - Northwest Agricultural & Forestry University
item Weng, Yiqun
item LI, Z - Northwest Agricultural & Forestry University

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2015
Publication Date: 9/1/2015
Publication URL: http://handle.nal.usda.gov/10113/61651
Citation: Tan, J., Tao, Q., Niu, H., Zhang, Z., Li, D., Gong, Z., Weng, Y., Li, Z. 2015. A novel allele of monoecious (m) locus is responsible for elongated fruit shape and perfect flowers in cucumber (Cucumis sativus L.). Theoretical and Applied Genetics. 128(12):2483-2493. doi: 10.1007/s00122-015-2603-0.

Interpretive Summary: In cucumber, sex determination is controlled primarily by the F and M genes. Homozygous recessive mm plants bear bisexual flowers and the fruits are often round shaped. CsACS2 encoding the 1-aminocyclopropane-1-carboxylic acid synthase has been shown to be the candidate gene for the m locus. We recently identified an andromonoecious cucumber line H38 that has bisexual flowers but elongated fruits. To clone the monoecious gene in H38, we developed a tri-parent mapping strategy, which took advantage of the high-density Gy14 × 9930 cucumber genetic map and the powder of bulk segregant analysis. TPMS allowed rapid location of the m-1 gene in H38 in cucumber chromosome 1. Further fine mapping revealed that a novel allele, m-1 in H38 controls the bisexual flower in H38, which was due to a 14 bp deletion in the third exon of the CsACS2 gene encoding a truncated loss-of-function protein of the cucumber ACS gene. Our study indicated that the TPMS is a useful strategy in rapidly cloning target genes. The new m-1 allele is a very important tool in understanding the molecular mechanisms of sex determination and fruit shape in cucumber.

Technical Abstract: In cucumber (Cucumis sativus L.), sex determination is controlled primarily by the F (female) and M (monoecy) loci. Homozygous recessive mm plants bear bisexual (perfect) flowers and the fruits are often round shaped. CsACS2 encoding the 1-aminocyclopropane-1-carboxylic acid synthase has been shown to be the candidate gene for the m locus. We recently identified an andromonoecious cucumber line H38 that has bisexual flowers but elongated fruits. To rapidly clone this monoecious gene in H38, we developed a tri-parent mapping strategy (TPMS), which took advantage of the high-density Gy14 × 9930 cucumber genetic map and the powder of bulk segregant analysis. Microsatellite markers from the Gy14 × 9930 map were used to screen two pairs of unisexual and bisexual bulks constructed, respectively, from the H38 ×Gy14 and H38 × 9930 F2 populations. Polymorphic markers were identified and used to develop a framework map and place the monoecious locus of H38 in cucumber chromosome 1. Further fine mapping allowed identification of a novel allele, m-1, at the monoecious locus in H38 to control the bisexual flower in H38, which was due to a 14 bp deletion in the third exon of the CsACS2 gene encoding a truncated loss-of-function protein of the cucumber 1-aminocyclopropane-1-carboxylic acid synthase. Our study indicated that the TPMS applied to cucumber can rapidly identify genomic regions covering a natural allele for a desired trait with limited primers. Using this method, a second independent mutatons in the CsACS2 gene shared with a same phenotype in flowers had been cloned, and it is concluded that the M locus encodes for CsACS2, which determines the monoecy in cucumber plant.