Novel approaches for understanding conifer seed dormancy and germination

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Some seeds germinate immediately upon their release from the parent plant as long as they encounter favorable environmental conditions. However, some seeds fail to germinate under favorable conditions, even though they are viable. These dormant seeds must be exposed to environmental cues such as periods of warm-dry conditions, moist chilling, or even smoke for dormancy to be terminated. The seeds of certain conifer (tree) species (e.g. yellow-cedar, western white pine and true firs) develop pronounced dormancy, exhibiting a low capacity for germination upon dispersal. The agricultural and forest industries rely upon seeds that exhibit high germination; hence dormancy is generally considered an undesirable trait. As well as developing tools for improving conifer seed germination, we have defined some of the factors that impose and maintain dormancy of conifer seeds. Our most striking discoveries in this regard concern the germination inhibitor abscisic acid (ABA), and a protein called ABI3, which helps to relay ABA signals. ABI3 proteins control many events that are critical to seed survival. This includes the deposition of food reserves, dormancy imposition and the acquisition of a tolerance of seed tissues to desiccation. In trees, the ABI3 protein may function as a global regulator, acting to regulate all key transitions during its lifecycle. The objectives of the proposed studies are: (1) To further our understanding of the role of ABI3 as a "gatekeeper" during important transitions of the lifecycle of trees: the dormancy-to-germination, germination-to-growth, and vegetative growth-to-reproductive growth (flowering) transitions. (2) To characterize novel regulators of dormancy and germination in conifer seeds. Understanding the mechanisms underlying the deep dormancy of conifer species will serve as an important model and will generate novel findings concerning the evolutionary conservation or divergence of genes and proteins involved in this critical adaptive trait.