Abstract
Seeds are complex biological systems comprising three genetically distinct tissues nested one inside another (embryo, endosperm, and maternal tissues). However, the complexity of the kernel makes it difficult to understand intercompartment interactions without access to spatially accurate information. Here, we took advantage of the large size of the maize (Zea mays) kernel to characterize genome-wide expression profiles of tissues at different embryo/endosperm interfaces. Our analysis identifies specific transcriptomic signatures in two interface tissues compared with whole seed compartments: the scutellar aleurone layer and the newly named endosperm adjacent to scutellum (EAS). The EAS, which appears around 9 d after pollination and persists for around 11 d, is confined to one to three endosperm cell layers adjacent to the embryonic scutellum. Its transcriptome is enriched in genes encoding transporters. The absence of the embryo in an embryo specific mutant can alter the expression pattern of EAS marker genes. The detection of cell death in some EAS cells together with an accumulation of crushed cell walls suggests that the EAS is a dynamic zone from which cell layers in contact with the embryo are regularly eliminated and to which additional endosperm cells are recruited as the embryo grows.
Highlights
Cereal grains are essential for plant propagation but are high-value products that represent an important source of calories and proteins for human nutrition and animal feed as well as a coveted resource for bio-sourced industries
From 8 to 9 d after pollination (DAP), the upper part forms two new interfaces: (1) at the adaxial side, the embryo is enclosed by a single cell layer, which is called the scutellar aleurone layer (SAL) in barley (Hordeum vulgare; Jestin et al, 2008); and (2) at the abaxial side, the embryo is brought into direct contact with central starchy endosperm (SE) cells (Van Lammeren, 1987)
The subcompartments corresponding to three distinct embryo/endosperm interfaces were the SAL, the apical scutellum (AS; corresponding to the embryo tip composed uniquely of scutellum tissues without the embryo axis), and a new region that we named the endosperm adjacent to scutellum (EAS), corresponding to several layers of endosperm cells in close contact with the scutellum at the abaxial side of the embryo (Figure 1; Supplemental Figure 1)
Summary
Cereal grains are essential for plant propagation but are high-value products that represent an important source of calories and proteins for human nutrition and animal feed as well as a coveted resource for bio-sourced industries. From 8 to 9 DAP, the upper part (embryo proper) forms two new interfaces: (1) at the adaxial side, the embryo is enclosed by a single cell layer, which is called the scutellar aleurone layer (SAL) in barley (Hordeum vulgare; Jestin et al, 2008); and (2) at the abaxial side, the embryo is brought into direct contact with central SE cells (Van Lammeren, 1987). This interface is constantly moving due to the growth of the scutellum inside the endosperm. The detection of cell death in the EAS together with the impaired expression of EAS marker genes in an embryo specific mutant suggest that the EAS is a developmentally dynamic interface influenced by the presence of the neighboring growing embryo
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