Cloning and mapping of the Brassica napus orthologs of the AtPirin gene associated with seed germination and seedling vigour, and generation of molecular markers to break the linkage with yellow seed colour in oilseed rape
Final Report Abstract
Yellow coloured seeds are of particular interest for oilseed rape (Brassica napus) breeding because of their association with a thinner seed coat resulting in reduced dietary fibre content. This considerably improves the meal and protein quality of rapeseed meal after oil extraction. On the other hand, yellow-seeded genotypes are often associated with negative agronomic characters including suppression of germination, inhibition of seedling development and reduced vigour. At the time this project was conceived, the available genomic synteny maps between B. napus and Arabidopsis thaliana implicated a Brassica orthologue of the gene AtPirin1, whose mutant in Arabidopsis influences seed germination and early seedling development, as a possible cause of these developmental deficiencies in yellow-seeded B. napus via linkage of a Bna.Pirin mutation to a major seed colour QTL on chromosome A09. Based on this hypothesis, the study aimed to use genetic and QTL mapping methods to develop molecular tools to break the presumed linkage drag between seed colour and germination/developmental deficiencies. High-throughput UPLC-MS/MS profiling of hormone metabolites in seeds and seedlings from black and yellow-seeded parental lines and a segregating DH population revealed a severe hormone imbalance in the yellow-seeded mutant 1012-98 as the cause of its disrupted germination and developmental phenotype. However, the mutations causing the hormonal imbalance were unexpectedly found to be inherited independently from the major QTL influencing seed colour. Detailed analysis of the parental genotypes uncovered apparent associations with mutations in hormone regulatory factor genes other than Bna.Pirin. In particular, B. napus orthologues of the key auxin response factor ARF10 exhibited amplification of C-genome copy number and transcript abundance, along with a chimeric allele originating from recombination between homoeologous A and C genome loci. Functional amino acid changes were also found in important DNA binding domains of one BnaC.ARF10 locus, potentially further increasing binding activity to auxin response genes. Cumulatively the results suggest that regulatory changes in Bna.ARF10 may be collectively responsible for the observed phenotypes in 1012-98. Using the detailed phenotype data obtained in this study in combination with high-throughput infra-red phenotyping of seed meal quality, we successfully selected wildtype Bna.ARF10 genotypes combining non-disturbed hormone profiles with low fibre content. Thus we were able to breed high-performing yellow-seeded oilseed rape lines with normal germination and vigour, and yield levels approaching those of elite, dark-seeded check varieties.
Publications
- A putative micro-RNA regulatory system influencing hormonal control of germination and seedling vigour in Brassica napus. "Genomics-based Breeding", Giessen, Germany, October 2010
Nguyen T, Friedt W, Abrams S, Zaharia I, Snowdon R
- Comparative mapping of QTL for hormone metabolites and developmental traits in oilseed rape seedlings. 17th Crucifer Genetics Workshop, Saskatoon, Canada, September 2010
Basunanda P, Salazar B, Zaharia I, Abrams S, Snowdon R
- Disruption of germination and seedling development in Brassica napus by mutations causing severe seed hormonal imbalance. Proceedings, 13th International Rapeseed Congress, Prague, Czech Republic, June 2011
Nguyen T, Obermeier C, Zaharia LI, Friedt W, Abrams SR, Snowdon RJ
