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Title: The gene CmACS-7 provides sequence variation for the development of DNA markers associated with monoecious sex expresion in melon (Cucumis melo L.)

Author
item NAMHUI, KIM - Pusan National University
item OH, JUYEOI - Agricultural Research And Extension Service, Korea
item KIM, BICHSEAM - Pusan National University
item CHOI, EUNG - Dongguk University
item HWANG, UN - Dongguk University
item Staub, Jack
item CHUNG, SANG-MIN - Dongguk University
item PARK, YOUNGHOOH - Pusan National University

Submitted to: Korean Society of Horticulture Science Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2015
Publication Date: 12/1/2015
Citation: Namhui, K., Oh, J., Kim, B., Choi, E., Hwang, U., Staub, J.E., Chung, S., Park, Y. 2015. The gene CmACS-7 provides sequence variation for the development of DNA markers associated with monoecious sex expresion in melon (Cucumis melo L.). Korean Society of Horticulture Science Journal. 56:535-545.

Interpretive Summary: In melon, different combinations and numbers of these flower types allow for the classification of plants. There is a need to produce sex stable lines and hybrids to optimize yield in melons, especially under environmental stress conditions. Thus, much research has focused on determining the underlying mechanisms of sex determination in melon. In South Korea, where high sugar muskmelon cultivars possessing compact netting are dominant most commercial parental inbred lines used in hybrid production (crossing two plants to produce seed) possess male and female sex organs in the same flowers. This requires hand pollinations (without bees) that is time consuming and costly. Thus, there is increasing interest by the seed industry to develop hybrid types that can be crossed using bees to reduce production costs. However, information on the genetics sex expression of Korean muskmelon is limited. Therefore, a study was designed to survey a genetically diverse array of Korean cultivars and develop biochemical tools that would be useful in selecting for melon types that would be relatively easy to cross with bees to produce hybrid melons. Through biochemical and genetic testing, the genes for sex expression in Korean melon were identified. This knowledge and its application in producing melon types that are amendable to crossing using bees will allow for a reduction in the costs of production of hybrid melons for diverse markers worldwide. This information also relates directly to U.S. production where hybrid melon seed is produced in greenhouses for sale to U.S. melon growers.

Technical Abstract: Most melon (Cucumis melo L.) breeding lines in South Korea display andromonoecious sex expression (i.e., possessing both bisexual and male flowers on the same plant), which, in turn, necessitates laborious hand emasculation during F1 hybrid seed production. Thus, there is a need to develop monoecious (possessing male and female flowers) sex types in elite germplasm to obviate self-pollination. Sex expression is associated with floral ethylene production, which, in monecious melon plants, is associated with the A locus. Hence a study was conducted to develop and test molecular markers for their use in the selection of monoecious plants based on sequence variation inherent in the CmACS-7 gene [1-aminocyclopropane-1-carboxylic acid synthase (ACS) activity] that is associated with ethylene production. Full-length CmACS-7 sequences were cloned from a monoecious (MO23) and andromonoecious (AM24) line. The alignment of those CmACS-7 sequences revealed a single nucleotide polymorphism (SNP; C170T) in exon 1 and an 18-bp indel in the 3'-untranslated region (UTR) of between MO23 and AM24, which was then used to develop a cleaved amplified polymorphic sequence (CAPS) (EX1-C170T) and sequence characterized amplified region (SCAR) marker (T1ex) from the SNP and indel, respectively. The sex expression and the T1ex SCAR-based genotype of 442 F2 plants derived from a line MO23 x AM24 cross was determined Monoecy and andromonoecy segregated in a 3:1 ratio in F2 progeny, where the sex type of 429 plants (13 plants not classified) co-segregated with the SCAR marker, demonstrating that sex expression regulated by CmACS-7 is controlled by a single dominant gene and that it confers monoecy in line MO23. Allelic variation in 112 geographically diverse melon lines for CmACS-7 as accessed by CAPS EX1-C170T and SCAR T1ex markers indicated that the: 1) exon 1 of CmACS-7 is highly conserved and the SNP/sex expression association detected is highly predictable making it potentially useful for marker-based selection of monoecious plants, and; 2) 18-bp indel mutation in the 3'-UTR was present in various lengths depending on different monoecious melon germplasm.