Identification of gene sequences involved in day length adaptation and nutritional quality in onion (Allium cepa L.)

Project summary

 Onion is the second most commonly grown vegetable in the  world. Genetic studies aimed at onion improvement have been  limited due to outcrossing and high heterozygosity of onion.  Onion bulb formation is highly sensitive to day length and the  varieties used are highly adapted to their local conditions. So,  day length regulation in onion is crucial for adapting new varieties  for growth and development under different latitudes. In  comparison to photoperiodic regulation of flowering, relatively little is known about genetic regulation of bulbing process.

This project aims to test the hypothesis that the genetic regulation of bulb formation is analogous to the genetic regulation of flowering and to identify gene sequences involved in day length adaptation and nutritional quality in onion. Methods that were used include bioinformatics analysis, transcriptome sequencing, RT-PCR and comparative studies on varieties adapted to long and short day production.

Project achievements

MLSRF has greatly assisted the research project. A comprehensive set of developmental and diurnal experiments have been set up to investigate the bulbing response and to generate materials for molecular analyses. Day length (LDs) dependent bulb initiation and development in Renate F1 onion was characterised. Bioinformatic analyses were performed to identify candidate genes in published database which have known function in Arabidopsis flowering and other developmental pathways, e.g., FT, CO, FLC, FD, SOC. Twenty-two partial cDNAs representing genes potentially involved in onion bulbing have been identified and isolated.

Eight of these were differentially expressed in bulb and leaf tissue and with respect to photoperiod. RNA-Seq analysis was performed using leaf and bulb materials of onion cv Renate F1 grown under long day (LD) and short day (SD) conditions to generate 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 of onion, respectively. I have attended supervisory meeting at least twice monthly intervals during project.

The data obtained from this research have been presented in two seminars (annual MIBTP seminar, the University of Leicester and the University of Warwick Crop Centre seminar, UK) and as a poster (the University of Warwick, UK) entitled “genetic regulation of day length adaptation in onion (Allium cepa L.). An article is processing based on differentially expressed genes identified in onion and it should go for publication at the end of this year when complete data will be analysed.

Md Harun Ar Rashid, School of Life Sciences, University Of Warwick