Parental and environmental control

Parental and environmental control of seed dormancy

Dormancy-specific genomic imprinting

Seed after-ripening time

Hybrid seeds

Seed dormancy is a trait of newly produced dry seeds that manifests itself by the absence of germination under otherwise favorable germination conditions. This trait is thought to prevent germination out of season while increasing the chances of seed dispersion. Dry seeds lose dormancy over time, also called dry after-ripening time, i.e. they become able to germinate when exposed to favorable germination conditions. The amount of dry after-ripening time needed to lose dormancy is used to define seed dormancy levels stored in dry seeds. Final dormancy levels vary among Arabidopsis accessions.

Remarkably, environmental conditions experienced by the mother plant influence the final dormancy levels stored in its seed progeny. Among those conditions, temperature is perhaps the single most influential factor regulating dormancy levels. In particular, Arabidopsis plants, as numerous other species, exposed to cold temperatures produce seeds with markedly higher dormancy levels. This adjustment is likely to play a major role in the control of plant phenology since it further influences the onset of germination.

In addition to its role to promote dormancy during seed maturation, de novo ABA synthesis upon seed imbibition is essential to repress the germination of dormant seeds. The endosperm plays an essential function in this context since germination occurs when the endosperm is removed, even in highly dormant seeds produced under cold temperatures (Piskurewicz et al. 2016).

Using the highly dormant Cvi ecotype in crosses with the low dormancy C24 and Col ecotypes, we observed that F1 seeds tend to inherit the dormancy levels more akin to their maternal genotype.
We wished to further understand the nature of the maternal regulation of seed dormancy levels independently of the temperature experienced by the mother plant.

We found that imprinted gene expression upon seed imbibition 1) occurs in the mature endosperm, mainly corresponding to maternally expressed genes (MEGs); 2) is observed in genes involved in the control of seed germination; 3) is dynamic taking place according to the dormancy levels present in the seed. Furthermore, we found that imprinted genes could regulate germination processes and that their preferential maternal allelic expression could implement maternal inheritance of seed dormancy levels (Piskurewicz et al. 2016).

We are currently addressing the question of the nature of the imprints sustaining genomic imprinting in the mature seed endosperm. Furthermore, given the regulation of dormancy levels by cold, we are also investigating the regulation of epigenetic marks by cold.