Embryo-Endosperm Interaction and Its Agronomic Relevance to Rice Quality

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.

Integration of embryo-endosperm interaction into a holistic and dynamic picture of seed development using a rice mutant with notched-belly grains

“…1). Since the formation of chalky tissue is a result of incomplete accumulation of starch and protein, it is tempting to speculate that the embryo plays a role in it, probably by depriving the nutrients from its proximate bottom endosperm (An et al, 2020). As revealed by our previous studies, the embryo demonstrated a negative effect on the contents of proteins, amino acids, and minerals in the chalky endosperm (Lin et al, 2016;Lin et al, 2017).…”

“…In addition, this comparison method revealed that the influence of embryo on IAA was (Ebisuya and Briscoe, 2018). There is evidence of bidirectional 4 interaction between embryo and endosperm throughout development (An et al, 2020).…”

“…The seed (grain) of rice (Oryza sativa) is a complex but delicate biological system, containing three genetically distinct tissues, the diploid embryo, the triploid endosperm, and the diploid maternal tissues (An et al, 2020). Concomitant development of embryo and endosperm under the constraint of maternal tissues requires coordination of the two compartments (Lafon-Placette and Köhler, 2014;Doll et al, 2020).…”

“…Growing evidence in rice as well as Arabidopsis (Arabidopsis thaliana) and maize (Zea mays) support bidirectional communication between embryo and endosperm. In brief, the endosperm plays crucial role in nurturing the developing embryo, whereas the embryo exerts a "counter-acting regulation force" on endosperm, as reviewed by An et al (2020) and Ingram (2020).…”

“…Consequently, a precise and 4 integrative landscape of seed development is necessary and useful for both fundamental and 4applied studies on the mechanisms underpinning crop yield and quality. Previously, from 4 viewpoint of crop physiology, we proposed a practical staging system with three phases: 4 embryo morphogenesis, endosperm filling, and seed maturation(An et al, 2020). Here, we 4 update this staging system by integrating of molecular, physiological, and anatomical 4 evidence in the current study as well as from the literature.…”