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Title: ACC Synthase Genes are Polymorphic in Watermelon (Citrullus spp.) and Differentially Expressed in Flowers and in Response to Auxin and Gibberellin

Author
item SALMAN, AYELET - BEN GURION UNIVERSITY
item Levi, Amnon
item WOLF, SHMUEL - HEBREW UNIVERSITY
item TREBITSH, TOVA - BEN GURION UNIVERSITY

Submitted to: Plant and Cell Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2008
Publication Date: 5/15/2008
Citation: Salman, A., Levi, A., Wolf, S., Trebitsh, T. 2008. Acc Synthase Genes are Polymorphic in Watermelon (citrullus spp.) and Differentially Expressed in Flowers and in Response to Auxin and Gibberellin. Plant And Cell Physiology. 49:740-750.

Interpretive Summary: Watermelon is a major vegetable crop in the U.S.A. In recent years, there has been an increased demand by consumers for small seedless watermelons, also known as “personal watermelons” or “mini watermelons”. Field studies showed that when watermelon plants produce high number of fruits (4-5 watermelon fruits per plant) their average size is significantly smaller compared with these on a plant having 1-2 fruits. Thus, seed companies and growers are interested in the development of varieties producing high numbers of small watermelon fruits. In this study, we examined a set of genes that control the formation of flowers that produce watermelon fruits. The gene sequences were examined in wild watermelon species producing high number of small fruits (6-8 fruits per plant) and were compared with these in watermelon cultivars producing a small number of large fruits (1-2 fruits per plant). The analysis revealed that there are significant differences in the DNA sequences of these genes between the wild type and watermelon cultivars. The findings in this study will be useful in further studies aiming to identify and isolate the genes controlling fruit production and in developing cultivars that produce high number of small watermelon fruits.

Technical Abstract: The flowering pattern of watermelon species (Citrullus) is either monoecious or andromonoecious. In watermelon (Citrullus lanatus L.), ethylene promotes male flower development while inhibitors of ethylene promote pistillate (pistil-bearing) flower formation. This is opposite to the feminizing effect of ethylene in other cucurbits such as cucumber and melon. In cucumber the rate-limiting enzyme of ethylene biosynthesis, 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS), regulates unisexual flower development. We wished to investigate the role of CitACS genes during unisexual flower development in watermelon. Four genomic sequences were isolated from watermelon (CitACS1-4). CitACS1 is expressed in vegetative tissue as well as in developing floral buds, and is up regulated by exogenous treatment with auxin, gibberellin or ACC, the immediate precursor of ethylene. No discernable differential floral sex-dependent expression pattern was observed for CitACS1. This gene may be involved in cell growth processes of floral organs consistent with the high transcript level that was detected in tendrils. The CitACS3 is expressed in open flowers and in young staminate floral buds (male or hermaphrodite) but not in female flowers. CitACS3 is also up regulated by ACC. This gene may be involved in ethylene-regulated anther development and then later in anther dehiscence. The expression CitACS2 was up regulated by auxin but undetectable in vegetative or reproductive organs. Expression of CitACS4 was non-detectable under our experimental conditions. Polymorphic CitACS markers can be useful in genetic studies to identify if any of the CitACS genes linked to flowering pattern in watermelon.