An Integrative Approach to Analyze Seed Germination in Brassica napus

Seed germination is a complex trait determined by the interaction of hormonal, metabolic, genetic, and environmental components. Previous studies of this process in crops have focused mainly on the analyses of one component of the regulatory events leading to seed germination. In the frame of an international collaboration lead by groups at the CBGP, a wide variety of global analyses together with an array of computational methods has been performed to dissect seed germination in Brassica napus (Oilseed rape), one of the world's most important sources of high-quality vegetable oil for human nutrition and vegetable protein diet for livestock. We have generated transcriptomic, metabolic, and hormonal data as well as scored different seed germination-associated traits at different stages upon seed imbibition. Using several accessions of B. napus and correlation analysis of all these data by computational methods, we have uncovered some of the major contributors to the variability of this trait: 1) seed germination speed; 2) the levels of malate and aspartate metabolites and 3) the hormonal balance between abscisic acid, gibberellins and auxin. In addition, specific regulatory genes have been identified as likely responsible for controlling germination speed. Finally, we have revealed that the physical interactions of these regulators with other regulatory partners seem to be conserved in other plant species, suggesting the existence of common regulatory strategies for this trait. Altogether, these results provide a comprehensive and detailed picture of seed germination dynamics in oilseed rape. This new framework will be extremely valuable not only to evaluate germination performance of B. napus accessions but also to identify key targets for crop improvement in this important process.