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ISHS Acta Horticulturae 1143: VII International Symposium on Edible Alliaceae

Genetic regulation of day length adaptation and bulb formation in onion (Allium cepa L.)

Authors:   M.H.A. Rashid, A.J. Massiah, B. Thomas
Keywords:   onion, bulb, day length, gene, transcriptome sequence
DOI:   10.17660/ActaHortic.2016.1143.2
Genetic studies aimed at onion improvement have been limited because of outcrossing, high heterozygosity, very large genome size with high level of repetitive DNA and limited sequence data. Onion bulb initiation is photoperiod-dependent and day length regulation in onion is crucial for adapting new cultivars for growth and development under different latitudes. In comparison to the photoperiodic regulation of flowering, relatively little is known about genetic regulation of the bulbing process. We are testing the hypothesis that the genetic regulation of bulb formation is analogous to the genetic regulation of flowering and aim to identify genes involved in day length adaptation in onion. A comprehensive set of developmental and diurnal experiments have been set up to investigate the bulbing response and to generate materials for molecular analyses. Bulbing ratios were used to measure the bulbing response of onion plants under long day (LD) and short day (SD) conditions, and the reversibility of the bulbing process. Twenty-two partial cDNAs representing genes potentially involved in onion bulbing have been identified and isolated. Eight of these were shown to be differentially expressed in bulb and leaf tissue and with respect to photoperiod. RNA-Seq analysis was performed to generate onion transcriptome reference sequence and for more widespread identification of genes differentially expressed in response to photoperiod. A total of 13665, 12604, 484 and 964 significantly differential expressed transcripts were detected in short day (SD) leaf vs. bulb, long day (LD) leaf vs. bulb, SD leaf vs. LD leaf and SD bulb vs. LD bulb, respectively.

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