Abstract
Seed germination is a complex trait determined by the interaction of hormonal, metabolic, genetic, and environmental components. Variability of this trait in crops has a big impact on seedling establishment and yield in the field. Classical studies of this trait in crops have focused mainly on the analyses of one level of regulation in the cascade of events leading to seed germination. We have carried out an integrative and extensive approach to deepen our understanding of seed germination in Brassica napus by generating transcriptomic, metabolic, and hormonal data at different stages upon seed imbibition. Deep phenotyping of different seed germination-associated traits in six winter-type B. napus accessions has revealed that seed germination kinetics, in particular seed germination speed, are major contributors to the variability of this trait. Metabolic profiling of these accessions has allowed us to describe a common pattern of metabolic change and to identify the levels of malate and aspartate metabolites as putative metabolic markers to estimate germination performance. Additionally, analysis of seed content of different hormones suggests that hormonal balance between ABA, GA, and IAA at crucial time points during this process might underlie seed germination differences in these accessions. In this study, we have also defined the major transcriptome changes accompanying the germination process in B. napus. Furthermore, we have observed that earlier activation of key germination regulatory genes seems to generate the differences in germination speed observed between accessions in B. napus. Finally, we have found that protein–protein interactions between some of these key regulator are conserved in B. napus, suggesting a shared regulatory network with other plant species. Altogether, our 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.
Highlights
A plants life cycle starts with seed germination, a process aiming to produce a seedling able to grow, develop, and generate viable offspring
We use all of these measurements to assess the influence of each of these traits in the seed germination variability observed in the accessions by performing a Principal component analysis (PCA) as well as a correlationIntegrative Analyses of Oilseed Rape Germination analysis
Despite our accessions being very similar in terms of seed viability, major differences in seed germination were observed in to reach 50% of germination (T50) values, spanning 15 h between the fastest (C129) and slowest (C032)
Summary
A plants life cycle starts with seed germination, a process aiming to produce a seedling able to grow, develop, and generate viable offspring. Continuous interaction between environment and genotype allows seeds to germinate when conditions are suitable for plant growth (Kendall et al, 2011; Penfield and MacGregor, 2017). In crops, this trait seems to be controlled by several genes adding complexity to its study and their application in biotechnological and breeding programs. Seed germination encompasses a wide number of metabolic, hormonal, and molecular events aimed to timely produce the emergence of the embryo radicle through the surrounding seed tissues (Bewley, 1997; Holdsworth et al, 2008a). Improving germination in crops will require integrative approaches, combining a wide variety of global analyses (metabolic, molecular, and genomic analyses) with an array of computational methods
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