Abstract
To survive in the dry state, orthodox seeds acquire desiccation tolerance. As maturation progresses, the seeds gradually acquire longevity, which is the total timespan during which the dry seeds remain viable. The desiccation-tolerance mechanism(s) allow seeds to remain dry without losing their ability to germinate. This adaptive trait has played a key role in the evolution of land plants. Understanding the mechanisms for seed survival after desiccation is one of the central goals still unsolved. That is, the cellular protection during dry state and cell repair during rewatering involves a not entirely known molecular network(s). Although desiccation tolerance is retained in seeds of higher plants, resurrection plants belonging to different plant lineages keep the ability to survive desiccation in vegetative tissue. Abscisic acid (ABA) is involved in desiccation tolerance through tight control of the synthesis of unstructured late embryogenesis abundant (LEA) proteins, heat shock thermostable proteins (sHSPs), and non-reducing oligosaccharides. During seed maturation, the progressive loss of water induces the formation of a so-called cellular “glass state”. This glassy matrix consists of soluble sugars, which immobilize macromolecules offering protection to membranes and proteins. In this way, the secondary structure of proteins in dry viable seeds is very stable and remains preserved. ABA insensitive-3 (ABI3), highly conserved from bryophytes to Angiosperms, is essential for seed maturation and is the only transcription factor (TF) required for the acquisition of desiccation tolerance and its re-induction in germinated seeds. It is noteworthy that chlorophyll breakdown during the last step of seed maturation is controlled by ABI3. This update contains some current results directly related to the physiological, genetic, and molecular mechanisms involved in survival to desiccation in orthodox seeds. In other words, the mechanisms that facilitate that an orthodox dry seed is a living entity.
Highlights
The core of desiccation-tolerance responses is retained in orthodox seeds, this special adaptation is only present in the vegetative organs of non-vascular plants and few Angiosperm species (
It is noteworthy that chlorophyll breakdown during the last step of seed maturation is controlled by ABA insensitive-3 (ABI3)
Multi-omic analysis showed that several cell wall (CW)-related genes involved in processes such as the regulation of CW plasticity, organization, and dynamics are differentially modulated upon dehydration. These analyses suggest the importance of CW remodeling during the acquisition of desiccation tolerance [40,81,82]
Summary
The colonization of, and permanence in, land by plants was one of the most important events in the history of our planet [1]. The three main parts of the seed, embryo, endosperm, and seed coat undergo a series of developmental processes that converge in the production of a mature seed that is developmentally arrested, strongly desiccated, and metabolically quiescent [11,12] This dormancy state constitutes an adaptive trait limiting germination under environmental conditions that would promote optimal. The loss of water does not have the same intensity in all tissues of seeds (e.g., embryo) This delicate organ is protected from drying out by special mechanisms. This review contains current views directly related to physiological and molecular mechanisms involved in survival of severe desiccation in seeds. This review attempts to clarify the mechanisms of orthodox seeds that explain how life can continue in extreme conditions, including lack of water
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