Abstract
Based on prior knowledge and with the support of new methodology, solid progress in the understanding of seed life has taken place over the few last years. This update reflects recent advances in three key traits of seed life (i.e., preharvest sprouting, genomic imprinting, and stored-mRNA). The first breakthrough refers to cloning of the mitogen-activated protein kinase-kinase 3 (MKK3) gene in barley and wheat. MKK3, in cooperation with ABA signaling, controls seed dormancy. This advance has been determinant in producing improved varieties that are resistant to preharvest sprouting. The second advance concerns to uniparental gene expression (i.e., imprinting). Genomic imprinting primarily occurs in the endosperm. Although great advances have taken place in the last decade, there is still a long way to go to complete the puzzle regarding the role of genomic imprinting in seed development. This trait is probably one of the most important epigenetic facets of developing endosperm. An example of imprinting regulation is polycomb repressive complex 2 (PRC2). The mechanism of PRC2 recruitment to target endosperm with specific genes is, at present, robustly studied. Further progress in the knowledge of recruitment of PRC2 epigenetic machinery is considered in this review. The third breakthrough referred to in this update involves stored mRNA. The role of the population of this mRNA in germination is far from known. Its relations to seed aging, processing bodies (P bodies), and RNA binding proteins (RBPs), and how the stored mRNA is targeted to monosomes, are aspects considered here. Perhaps this third trait is the one that will require greater experimental dedication in the future. In order to make progress, herein are included some questions that are needed to be answered.
Highlights
Key Biological Traits about Seed Dormancy and Germination Mechanisms The seed stage is a key life-cycle stage for many plants
Early seedling growth is supported by catabolism of stored reserves of protein, oil, or starch accumulated in stored tissues during seed maturation [1,2,3,4]. (ii) Germination on the mother plant, can occur in crops, which is an agronomically and industrially undesired trait that compromises yield, nutritional and processing quality
Orthodox seeds acquire dormancy by avoiding PHS [5,6,7]. (iii) Orthodox and viable dry seeds are alive because they have acquired desiccation resistance, a feature accomplished together with longevity at the beginning of maturation [8,9,10,11]. (iv) Interestingly, dry and viable seeds store a multitude of transcripts to be used at the beginning of the germination process [12,13]. (v) Reactive oxygen species (ROS) and nitric oxide (NO) play fundamental roles in seed-life [14,15,16,17]. (vi) All the above vital events that occur in seeds are coordinated by transcription factors (TFs) such as ABI3, ABI4, and ABI5 [18,19,20,21,22,23], and phytohormones, being the regulatory mechanisms underlying abscisic acid (ABA) and gibberellins (GAs) crosstalk, intensively documented during seed dormancy and germination
Summary
Key Biological Traits about Seed Dormancy and Germination Mechanisms The seed stage is a key life-cycle stage for many plants. The seeds of several species are used as biological systems in order to advance knowledge of the complex puzzle that constitutes the seed life and perpetuation of these entities that have been key in the colonization of dry land [36]. This update summarizes recent breakthroughs in our knowledge of some aspects highly involved in the life of orthodox seeds
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