Abstract
Seed dormancy is a genetically controlled block preventing the germination of imbibed seeds in favorable conditions. It requires a period of dry storage (after-ripening) or certain environmental conditions to be overcome. Dormancy is an important seed trait, which is under selective pressure, to control the seasonal timing of seed germination. Dormant and non-dormant (after-ripened) seeds are characterized by large sets of differentially expressed genes. However, little information is available concerning the temporal and spatial transcriptional changes during early stages of rehydration in dormant and non-dormant seeds. We employed genome-wide transcriptome analysis on seeds of the model plant Arabidopsis thaliana to investigate transcriptional changes in dry seeds upon rehydration. We analyzed gene expression of dormant and after-ripened seeds of the Cvi accession over four time points and two seed compartments (the embryo and surrounding single cell layer endosperm), during the first 24 h after sowing. This work provides a global view of gene expression changes in dormant and non-dormant seeds with temporal and spatial detail, and these may be visualized via a web accessible tool (http://www.wageningenseedlab.nl/resources). A large proportion of transcripts change similarly in both dormant and non-dormant seeds upon rehydration, however, the first differences in transcript abundances become visible shortly after the initiation of imbibition, indicating that changes induced by after-ripening are detected and responded to rapidly upon rehydration. We identified several gene expression profiles which contribute to differential gene expression between dormant and non-dormant samples. Genes with enhanced expression in the endosperm of dormant seeds were overrepresented for stress-related Gene Ontology categories, suggesting a protective role for the endosperm against biotic and abiotic stress to support persistence of the dormant seed in its environment.
Highlights
Seeds are complex, stress-resistant plant structures with two major functions: reproduction and dispersal
Imbibed seeds were dissected into two distinct compartments, the micropylar and chalazal end of the endosperm (MCE), which acts as a barrier together with the seed coat, and the combined radicle and hypocotyl (RAD; Figure 1C), which has to expand to break through the covering layers to complete seed germination
Seeds over the first 24 hours after sowing (HAS) of two seed compartments that are important in the regulation of seed dormancy and germination (Nonogaki, 2014; Bassel, 2016)
Summary
Stress-resistant plant structures with two major functions: reproduction and dispersal. In Arabidopsis, seed dormancy is classified as ‘non-deep physiological dormancy’ [in common with seeds of most weeds, vegetables, and many garden flowers (Baskin and Baskin, 2014)] and is usually broken by relatively short periods of cold stratification or dry seed storage at room temperature (a process known as after-ripening; Finch-Savage and Leubner-Metzger, 2006; Bewley et al, 2013; Baskin and Baskin, 2014). The depth of dormancy in fully matured seeds is determined both by environmental conditions, temperature, experienced by the mother plant (Fenner, 1991; Kendall and Penfield, 2012; Chen et al, 2014; He et al, 2014) as well as genetic factors (Bentsink et al, 2007; Bentsink and Koornneef, 2008). Genetic variation for seed dormancy has been explored by genome wide association studies, as well as quantitative trait loci (QTL) mapping (Alonso-Blanco et al, 2003; Bentsink et al, 2010; Yano et al, 2013)
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