Abstract
Embryo-endosperm interaction is the dominant process controlling grain filling, thus being crucial for yield and quality formation of the three most important cereals worldwide, rice, wheat, and maize. Fundamental science of functional genomics has uncovered several key genetic programs for embryo and endosperm development, but the interaction or communication between the two tissues is largely elusive. Further, the significance of this interaction for grain filling remains open. This review starts with the morphological and developmental aspects of rice grain, providing a spatial and temporal context. Then, it offers a comprehensive and integrative view of this intercompartmental interaction, focusing on (i) apoplastic nutrient flow from endosperm to the developing embryo, (ii) dependence of embryo development on endosperm, (iii) regulation of endosperm development by embryo, and (iv) bidirectional dialogues between embryo and endosperm. From perspective of embryo-endosperm interaction, the mechanisms underlying the complex quality traits are explored, with grain chalkiness as an example. The review ends with three open questions with scientific and agronomic importance that should be addressed in the future. Notably, current knowledge and future prospects of this hot research topic are reviewed from a viewpoint of crop physiology, which should be helpful for bridging the knowledge gap between the fundamental plant sciences and the practical technologies.
Highlights
Rice (Oryza sativa) is a model plant for genomic studies, through which the genes discovered provide fundamental insight into the complex and dynamic processes governing plant life
Substantial influence of the embryo on endosperm composition was revealed, with the embryo negatively affecting the storage of total protein, amino acids, and minerals in the chalky endosperm (Lin et al, 2016). This was associated with the upregulation of genes responsible for the transporters for metabolites and the signal messengers of hormones in the chalky endosperm, and embryo may be involved in regulating the nutrient distribution within the seed (Lin et al, 2017)
Recent advances in Arabidopsis and maize have conformed substantial bidirectional interactions between embryo and endosperm during seed development, indicating that the interplay of the two compartments should be common among plant species
Summary
Rice (Oryza sativa) is a model plant for genomic studies, through which the genes discovered provide fundamental insight into the complex and dynamic processes governing plant life. Endosperm is composed of two tissues, starchy endosperm and the aleurone. Milling has a substantial influence on rice quality and value, by removing the embryo, the maternal tissues, the aleurone, and even part of starchy endosperm depending on the degree of milling. The remaining part of the grain, milled rice, is the starchy endosperm that mainly composed of starch and protein. Rice quality traits are dependent on the physico-chemical properties of starchy endosperm. For eating quality, it is coordinately controlled by amylose, amylopectin, proteins, and lipids (Bhattacharya, 2011). Fundamental science of functional genomics has uncovered some key mechanisms regulating embryo and endosperm development, but the interaction or communication between the two tissues is largely elusive. Current knowledge and future prospects of this hot research topic are reviewed from a viewpoint of crop physiology, which should be helpful for bridging the knowledge gap between the fundamental plant science (gene study) and the practical technology (crop breeding and management)
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