Lehrstuhl für Pflanzenzüchtung

Unraveling the Genetic Mechanisms of Flowering Time Control in Rapeseed

 

Flowering time control in rapeseed

Background

The optimal time for flowering varies between crop plants and depends on diverse factors such as the type of product (e.g., fruit or root crop), the cultivar (e.g., spring or winter types) and the climate of the cultivated area. Identification of genes that promote or inhibit flowering may hold an important key for sustainable agriculture under distinct environmental conditions. Considering the increasing evidences suggesting that flowering time regulators may influence hybrid vigor and subsequently plant’s yield, understanding the mechanisms governing flowering time and vernalization requirement in oilseed rape (Brassica napus L.), one of the major sources of edible oil worldwide, can guarantee successful reproduction and seed development which is crucial for rapeseed considering its economic importance in human and animal feeding. In Arabidopsis, a model plant closely related to Brassica species, the main regulatory pathways for flowering time have been uncovered in the last decade. However, despite a close phylogenetic relation, transfer of information from Arabidopsis to B. napus is hindered by the allopolyploid nature of the oilseed rape genome.

Objectives

  • A comprehensive survey of flowering time genes in B. napus to detect yet unknown flowering regulators by transcriptome analysis, promotor analysis, linkage mapping, and association mapping of candidate gene orthologs.
  • The detection and phenotypic evaluation of new flowering time mutants and sequence variants by TILLING and allele mining in gene bank populations

Results

For TILLING in B. napus flowering time genes, more than 3500 M3 plants (>2100 M1 plants) were screened for mutations in three target genes, starting from EMS-mutagenized seeds of the winter-type cultivar Express 617. We have detected more than 110 EMS-generated alleles in paralogs of major flowering time regulators,  FRIGIDA (FRI),  FLOWERING LOCUS-T (FT), and TERMINAL FLOWER-1 (TFL1). Surprisingly, single locus mutations in BnFRI and BnFT have shown effects in flowering time and vernalization responses despite the existence of several gene-copies. Mutations within BnTFL1 paralog had no large effects on flowering time but on yield components. F1 hybrids between BnTFL1 mutants and non-mutated parents had increased seed number per pod and total seeds per plant suggesting that heterozygous mutations in a TFL1 paralog may impact heterosis in rapeseed.

To gain a deeper insight into genetic factors controlling floral transition in B. napus, RNA-seq has been performed in the semi-winter doubled haploid line Ningyou7. The expression profiles of more than 58,000 gene models were analyzed by iterative RNA-seq-quantification and RT-qPCR validation cycles.  Many genes were differentially regulated between BBCH30 vernalized (V30) and non-vernalized (NV30) conditions,. Some flowering time regulators showed association with flowering time and/or yield. Preliminary results suggest that within groups of known flowering time regulators, some paralogs show expression dynamics consistent to those of the Arabidopsis orthologs. However, considerable expression variability is also observed between very similar paralogs, showing evidences of sub-functionalization. The present results shed new light on the interaction of paralog genes in a polyploid plant species. Furthermore, the EMS generated alleles constitute a new source of genetic variation for rapeseed breeding.

Project team

Bettina Rohardt
M.Sc. Smit Shah
Dr. Nazgol Emrani
Prof. Dr. Christian Jung

Scientific Partners

Prof. Ivo Grosse, Institute of Computer Science, Martin-Luther-University Halle-Wittenberg, Germany
Prof. Jingling Meng, Huazhong Agricultural University, Wuhan, China
Prof. Wei Qian, Southwest University, Chongqing, China
Prof. Habibur Rahman, University of Alberta, Canada
Prof. Rod Snowdon, University of Giessen, Germany
Dr. Markus Schilhabel, Institut für Klinische Molekularbiologie (IKMB) Kiel, Germany

Commercial Partners

Norddeutsche Pflanzenzucht Hans-Georg Lembke KG (NPZ)

Publications

Guo, Y., H. Harloff, et al. (2014). Mutations in single FT and TFL1 paralogs of rapeseed (Brassica napus L.) and their impact on flowering time and yield components. Frontiers in Plant Science 5: 282

Zou X, Suppanz I, Raman H, Hou J, Wang J, et al. (2012) Comparative Analysis of FLC Homologues in Brassicaceae Provides Insight into Their Role in the Evolution of Oilseed Rape. PLoS ONE 7(9): e45751. doi:10.1371/journal.pone.0045751

Wang, N., Qian, W., Suppanz, I., Wei, L. , Mao, Z., Long, Y., Meng, J., Müller, A. E. and Jung, C. (2011) Flowering time variation in oilseed rape (Brassica napus L.) is associated with allelic variation in the FRIGIDA homologue BnaA.FRI.a. Journal of Experimental Botany, 62:5641-58

Financial Support

Funding is provided by the DFG Priority Program 1530: Flowering Time Control – from Natural Variation to Crop Improvement

Updated: 30.08.2016          Responsible for this webpage: M.Sc. Smit Shah