Abstract
The life of a plant is characterized by major phase transitions. This includes the agriculturally important transitions from seed to seedling (germination) and from vegetative to generative growth (flowering induction). In many plant species, including Arabidopsis thaliana, freshly harvested seeds are dormant and incapable of germinating. Germination can occur after the release of dormancy and the occurrence of favourable environmental conditions. Although the hormonal control of seed dormancy is well studied, the molecular mechanisms underlying the induction and release of dormancy are not yet understood.In this study, we report the cloning and characterization of the mutant reduced dormancy 2-1 (rdo2-1). We found that RDO2 is allelic to the recently identified dormancy gene TFIIS, which is a transcription elongation factor. HUB1, which was previously called RDO4, was identified in the same mutagenesis screen for reduced dormancy as rdo2-1 and was also shown to be involved in transcription elongation. The human homologues of RDO2 and HUB1 interact with the RNA Polymerase II Associated Factor 1 Complex (PAF1C). Therefore, we investigated the effect of other Arabidopsis PAF1C related factors; VIP4, VIP5, ELF7, ELF8 and ATXR7 on seed dormancy. Mutations in these genes resulted in reduced dormancy, similar to hub1-2 and rdo2-1. Consistent with a role at the end of seed maturation, we found that HUB1, RDO2 and VIP5 are upregulated during this developmental phase. Since mutants in PAF1C related factors are also described to be early flowering, we conclude that these components are involved in the regulation of both major developmental transitions in the plant.
Highlights
Germination and induction of flowering are important developmental switches in the life cycle of plants
In this work we demonstrate that the rdo2 mutation, isolated in the same screen as rdo4/hub1 [9], is allelic to TFIIS
This combination of domains is characteristic for Transcription elongation factor SII (TFIIS) [18]
Summary
Germination and induction of flowering are important developmental switches in the life cycle of plants. Seed dormancy is defined as the incapacity of a viable seed to germinate and evolved in plants to survive periods of unfavourable environmental conditions like dry summers. In many plant species, including the model plant Arabidopsis thaliana, primary seed dormancy is induced during the seed maturation phase and is highest in freshly harvested seeds. Dormancy is released by imbibition of seeds at low temperatures (stratification) or by dry storage (after-ripening). Germination requires the protrusion of the radicle through the surrounding structures (endosperm and testa in Arabidopsis) and can occur when non-dormant seeds meet permissive environmental conditions regarding humidity, light and temperature [1]. In some crops, including cereals, very low dormancy levels can lead to pre-harvest sprouting and reduced product quality [2]
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