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Transcriptional repression specifies the central cell for double fertilization.

ABSTRACT: Double fertilization is a key innovation for the evolutionary success of angiosperms by which the two fertilized female gametes, the egg cell and central cell, generate the embryo and endosperm, respectively. The female gametophyte (embryo sac) enclosed in the sporophyte is derived from a one-celled haploid cell lineage. It undergoes successive events of mitotic divisions, cellularization, and cell specification to give rise to the mature embryo sac, which contains the two female gametes accompanied by two types of accessory cells, namely synergids and antipodals. How the cell fate of the central cell is specified has long been equivocal and is further complicated by the structural diversity of female gametophyte across plant taxa. Here, MADS-box protein AGL80 was verified as a transcriptional repressor that directly suppresses the expression of accessory cell-specific genes to specify the central cell. Further genetic rescue and phylogenetic assay of the AGL80 orthologs revealed a possible conserved mechanism in the Brassicaceae family. Results from this study provide insight into the molecular determination of the second female gamete cell in Brassicaceae.

SUBMITTER: Zhang MX

PROVIDER: S-EPMC7084083 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Transcriptional repression specifies the central cell for double fertilization.

Zhang Meng-Xia MX Zhu Shan-Shan SS Xu Yong-Chao YC Guo Ya-Long YL Yang Wei-Cai WC Li Hong-Ju HJ

Proceedings of the National Academy of Sciences of the United States of America 20200304 11

Double fertilization is a key innovation for the evolutionary success of angiosperms by which the two fertilized female gametes, the egg cell and central cell, generate the embryo and endosperm, respectively. The female gametophyte (embryo sac) enclosed in the sporophyte is derived from a one-celled haploid cell lineage. It undergoes successive events of mitotic divisions, cellularization, and cell specification to give rise to the mature embryo sac, which contains the two female gametes accompa ...[more]

PMID: 32132210

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Project description:During double fertilization in angiosperms, two male gametes (sperm cells), are released from a pollen tube into the receptive region between two female gametes; the egg cell and the central cell of the ovule. The sperm cells fertilize the egg cell and the central cell in a one-to-one manner to yield a zygote and an endosperm, respectively. The one-to-one distribution of the sperm cells to the two female gametes is strictly regulated, possibly via communication among the four gametes. Polyspermy block is the mechanism by which fertilized female gametes prevent fertilization by a secondary sperm cell, and has been suggested to operate in the egg cell rather than the central cell. However, whether the central cell also has the ability to avoid polyspermy during double fertilization remains unclear. Here, we assessed the one-to-one fertilization mechanism of the central cell by laser irradiation of the female gametes and live cell imaging of the fertilization process in Arabidopsis thaliana. We successfully disrupted an egg cell within the ovules by irradiation using a femtosecond pulse laser. In the egg-disrupted ovules, the central cell predominantly showed single fertilization by one sperm cell, suggesting that neither the egg cell nor its fusion with one sperm cell is necessary for one-to-one fertilization (i.e., monospermy) of the central cell. In addition, using tetraspore mutants possessing multiple sperm cell pairs in one pollen, we demonstrated that normal double fertilization was observed even when excess sperm cells were released into the receptive region between the female gametes. In ovules accepting four sperm cells, the egg cell never fused with more than one sperm cell, whereas half of the central cells fused with more than one sperm cell (i.e., polyspermy) even 1 h later. Our results suggest that the central cell can block polyspermy during double fertilization, although the central cell is more permissive to polyspermy than the egg cell. The potential contribution of polyspermy block by the central cell is discussed in terms of how it is involved in the one-to-one distribution of the sperm cells to two distinct female gametes.

Project description:The zebrafish u-boot (ubo) gene encodes the transcription factor Prdm1, which is essential for the specification of the primary slow twitch muscle fibres that derive from adaxial cells. Here we show that Prdm1 executes this function by acting as a transcriptional repressor. Expression of the slow twitch isoform of the myosin heavy chain in adaxial cells is achieved by Prdm1 mediated repression of the transcriptional repressor Sox6. Using Chromatin immuno precipitation (ChIP) we found that genes encoding fast specific isoforms of sarcomeric proteins are direct targets of Prdm1. These genes are ectopically expressed in the adaxial cells of ubotp39 mutant embryos, suggesting that Prdm1 promotes slow twitch fibre differentiation by acting both as a global repressor of fast fibre specific genes as well as of a repressor of slow specific genes. Keywords: ChIP-chip Genomic array design. Microarrays were designed as described below and manufactured by Agilent Technologies (www.agilent.com). We have previously described the ChIP-chip technique in zebrafish and the design of promoter microarrays which cover a 2kb region around the transcription start sites (TSSs) of 11,512 zebrafish genes based on Zv4 (Wardle et al, 2006. Genome Biology 7:R71). In order to capture additional regulatory information further from the basal promoter region we also designed an expanded set of 60mer probes that cover 9kb upstream and 3kb downstream of the TSS of these genes using the same parameters as for the 2kb microarrays. These probe sequences were re-mapped to Zv6 over the course of the project and the coordinates given are for Zv6. We also incorporated several sets of control probes, both positive and negative. On each array there are 769 negative probes designed against zebrafish gene desert regions and Arabidopsis thaliana genes. In addition we included duplicates of promoter probes for several genes that we anticipated may be bound by factors of interest for this and other studies (tnnt3a, mylz2, myhz2, wnt11, flh, vent, msgn1, myod, fgf8, pcdh8) and these probes are arrayed on both slides slide. Finally on each array there are 1804 controls added by Agilent. The final design contained 352,490 probes divided between two microarray slides. Further information on design and manufacture of the microarrays can be found at the Agilent Technologies website.

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Transcriptional repression specifies the central cell for double fertilization.

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Transcriptional repression specifies the central cell for double fertilization.

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