Awake1, an ABC-Type Transporter, Reveals an Essential Role for Suberin in the Control of Seed Dormancy.

The mother plant plays an important dynamic role in the control of dormancy of her progeny seed in response to environmental signals. In order to further understand the mechanisms by which this dormancy control takes place in Arabidopsis (Arabidopsis thaliana), we conducted a forward genetic screen to isolate mutants that fail to enter dormancy in response to variation in temperature during seed set. We show that, for the first of these mutants, designated awake1, the maternal allele is required for entry into strongly dormant states and that awake1 mutants show seed phenotypes shown previously to be associated with the loss of suberin in the seed. We identify awake1 as an allele of ABCG20, an ATP-binding cassette transporter-encoding gene required for the transport of fatty acids during suberin deposition, and show that further suberin-deficient mutants have seed dormancy defects. Seed coat suberin composition is affected by temperature during seed maturation, but this response appears to be independent of ABCG20. We conclude that seed coat suberin is essential for seed dormancy imposition by low temperature and that the exclusion of oxygen and water from the seed by the suberin and tannin layers is important for dormancy imposition.

Seed production temperature regulation of primary dormancy occurs through control of seed coat phenylpropanoid metabolism.

Environmental changes during seed production are important drivers of lot-to-lot variation in seed behaviour and enable wild species to time their life history with seasonal cues. Temperature during seed set is the dominant environmental signal determining the depth of primary dormancy, although the mechanisms though which temperature changes impart changes in dormancy state are still only partly understood. We used molecular, genetic and biochemical techniques to examine the mechanism through which temperature variation affects Arabidopsis thaliana seed dormancy. Here we show that, in Arabidopsis, low temperatures during seed maturation result in an increase in phenylpropanoid gene expression in seeds and that this correlates with higher concentrations of seed coat procyanidins. Lower maturation temperatures cause differences in coat permeability to tetrazolium, and mutants with increased seed coat permeability and/or low procyanidin concentrations are less able to enter strongly dormant states after exposure to low temperatures during seed maturation. Our data show that maternal temperature signalling regulates seed coat properties, and this is an important pathway through which the environmental signals control primary dormancy depth.