Preface

Different recent studies have discovered new exciting knowledge concerning seed dormancy and germination. Among the most significant discoveries are probably the epigenetic mechanisms controlling seed dormancy entry and release and germination events. While bioinformatics and systems biology have been employed in generating new hypotheses, experimental biology is being used to test them using different molecular tools such as the characterization of "seed dormancy mutants," the research outcomes if which look very conclusive and promising. More progress in seed dormancy and germination research will be necessary to reach new physiological understandings. Probing new hypotheses and using forward genetics and biochemical and molecular approaches seem to be the chosen ways for exploring emerging mechanisms to provide an overview of the frontier of this field.

Seed dormancy has played a significant role in the adaptation and evolution of seed plants. Its biological significance is clear; however, much more progress has to be made regarding the molecular mechanisms underlying seed dormancy induction, maintenance, and alleviation, which still remain elusive. The hormonal contribution to these processes, i.e. gibberellin and abscisic acid metabolism in seeds, has greatly added substantial insights into the current understanding of seed dormancy.

Interestingly, other mechanisms such as chromatin remodeling through histone modification, i.e. ubiquitination, methylation, and acetylation, could lead to transcription activation or gene silencing, critical for seed dormancy regulation. Furthermore, small interfering RNA and/or long non-coding RNA might be a trigger of epigenetic changes at the seed dormancy or germination stages.

Therefore, appropriate distribution of seed germination, in both temporal and spatial fashion, is critical for the survival and propagation of seed plants. Spatial distribution of germination is usually controlled through seed and fruit morphology, which improves seed offspring spreading. In contrast, temporal distribution of germination is mostly controlled by the physiological conditions of seeds. A difference in the physiological status among individual seeds in a population allows each seed to germinate at a different timing, which is an important strategy for seeds to avoid different backward situations such as competition with their relatives, while abolishing extinction of all individuals due to unsuitable environmental conditions. Plants have evolved acquiring seed dormancy and temporal suppression of germination under conditions favorable to germination. Induction of seed dormancy during the maturation stage and its release in a dry state after a certain period of time ("after-ripening") are extensive phenomena that can be observed in several species of seed plants.

There may be a universal mechanism of seed dormancy as well as a species-specific variation in the regulatory mechanisms. The progress in basic and applied seed

science will enable knowledge translation, another frontier of research to be expanded for food production improvements with lower inputs in agriculture.

> **Dr. Jose Carlos Jimenez-Lopez** Spanish National Research Council (CSIC), Spain

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Section 1

Dormancy Process
