Endosperm Origin, Development, and Function

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345

Higher plant reproduction is unique because two cells are fertilized in the haploid female gametophyte. Egg and sperm nuclei fuse to form the embryo. A second sperm nucleus fuses with the central cell nucleus that replicates to generate the endosperm, a tissue that supports embryo development. To understand mechanisms that initiate reproduction, we isolated a mutation in Arabidopsis, f644, that allows for replication of the central cell and subsequent endosperm development without fertilization. When mutant f644 egg and central cells are fertilized by wild-type sperm, embryo development is inhibited, and endosperm is overproduced. By using a map-based strategy, we cloned and sequenced the F644 gene and showed that it encodes a SETdomain polycomb protein. Subsequently, we found that F644 is identical to MEDEA (MEA), a gene whose maternal-derived allele is required for embryogenesis [Grossniklaus, U., VielleCalzada, J.

mentioning

confidence: 99%

“…The endosperm (Fig. 2H) produces storage proteins, starch, and lipids, all of which are taken up by the developing embryo (1).…”

mentioning

confidence: 99%

Control of fertilization-independent endosperm development by the MEDEA polycomb gene in Arabidopsis

Kiyosue

Ohad

Yadegari

et al. 1999

334

345

“…The primary endosperm nucleus undergoes a series of mitotic divisions to produce nuclei that migrate into the expanding central cell (5,6). Cytokinesis sequesters endosperm cytoplasm and nuclei into discrete cells (7) that produce storage proteins, starch, and lipids that support embryo growth (8). Fertilization also activates development of the integument cell layers (Fig.…”

mentioning

confidence: 99%

A mutation that allows endosperm development without fertilization.

Ohad¹,

Margossian²,

Hsu³

et al. 1996

366

355

The mechanisms that initiate reproductive development after fertilization are not understood. Reproduction A fundamental problem in biology is to understand how fertilization initiates reproductive development. As shown in Fig. 1, in higher plants, the ovule generates the female gametophyte, which is composed of egg, central, synergid, and antipodal cells (1). All are haploid except the central cell, which contains two daughter nuclei that fuse before fertilization. One sperm nucleus fertilizes the egg to form the zygote, whereas another sperm nucleus fuses with the diploid central cell nucleus to form the triploid endosperm nucleus (2). The two fertilization products undergo distinct patterns of development. In Arabidopsis, the embryo passes through a series of stages that have been defined morphologically as preglobular, globular, heart, cotyledon, and maturation (3, 4). The primary endosperm nucleus undergoes a series of mitotic divisions to produce nuclei that migrate into the expanding central cell (5, 6). Cytokinesis sequesters endosperm cytoplasm and nuclei into discrete cells (7) that produce storage proteins, starch, and lipids that support embryo growth (8). Fertilization also activates development of the integument cell layers (Fig. 1) of the ovule that become the seed coat and induces the ovary (Fig. 1)

“…In addition, endosperm is an attractive system for developmental biology studies because of its simple anatomy, the mature grain consisting of three cell types, the aleurone layer, the starchy endosperm, and the transfer layer (1)(2)(3)(4). The endosperm develops from the fertilized central cell of the megagametophyte or embryo sac.…”

mentioning

confidence: 99%

sal1 determines the number of aleurone cell layers in maize endosperm and encodes a class E vacuolar sorting protein

Shen

Zhao

et al. 2003

129

109

A microscopy-based screen of a large collection of maize Mutator (Mu) transposon lines identified the supernumerary aleurone layers 1-1 (sal1-1) mutant line carrying up to seven layers of aleurone cells in defective kernel endosperm compared with only a single layer in wild-type grains. Normal, well filled endosperm that is homozygous for the sal1-1 mutant allele contains two to three layers of aleurone cells. Cloning of the sal1 gene was accomplished by using Mu tagging, and the identity of the cloned gene was confirmed by isolating an independent sal1-2 allele by reverse genetics. Homozygous sal1-2 endosperm has two to three layers of aleurone cells in normal, well filled grains. In situ hybridization experiments reveal that the sal1 gene is ubiquitously expressed in vegetative as well as zygotic grain tissues, with no difference being detected between aleurone cells and starchy endosperm cells. Northern blot analysis failed to detect the sal1-2 transcript in leaves of homozygous plants, suggesting that the allele is a true sal1 knockout allele. The sal1 gene encodes a homologue of the human Chmp1 gene, a member of the conserved family of the class E vacuolar protein sorting genes implicated in membrane vesicle trafficking. In mammals, CHMP1 functions in the pathway targeting plasma membrane receptors and ligands to lysosomes for proteolytic degradation. Possible roles for the function of the sal1 gene in aleurone signaling, including a defect in endosome trafficking, are discussed.