Transcriptional repression specifies the central cell for double fertilization

First author: Meng-Xia Zhang; Affiliations: CAS Institute of Genetics and Developmental Biology (中科院遗传与发育生物学研究所): Beijing, China

Corresponding author: Hong-Ju Li

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.

双受精（double fertilization）是被子植物演化成功的关键创新之一，由两种受精的雌配子，分别为卵细胞（egg cell）和中央细胞（central cell），形成胚胎和胚乳组织。包含在孢子体内的雌配子体，即胚囊（embryo sac），来源于单个细胞的单倍体细胞系。它会连续经历有丝分裂、细胞化以及细胞特化事件，发育为成熟的胚囊，其包含两个雌配子，并伴有两种类型的辅助细胞，即助细胞（synergid）和反足细胞（antipodal）。长期以来，中央细胞的细胞命运如何特化的一直模糊不清，并且由于整个植物类群中雌配子体的结构十分多样化，使得该方向的研究变得更加复杂。本文中，作者发现MADS-box蛋白AGL80作为一个转录抑制子，能够直接抑制辅助细胞特异基因的表达，从而维持中央细胞的特化。进一步的遗传拯救试验以及系统发育分析显示十字花科家族不同物种之间具有保守的AGL80功能。本文的研究为十字花科中控制中央细胞细胞命运的分子机制提供了新的视野。

Significance

Double fertilization is a key innovation of flowering plants. The central cell is the second female gamete, and its fertilization gives rise to the endosperm, the nurse of a seed. However, how this cell is specified and evolved in angiosperm remains unknown. This study reveals a transcriptional repression mechanism to specify the central cell in Arabidopsis and provides insight into the origination of this mechanism in Brassicaceae.

双受精是有花植物最关键的创新之一。中央细胞作为第二个雌配子，其在受精后会形成种子胚胎发育的主要营养供给组织～胚乳。然而，中央细胞是如何特化的以及在被子植物中的起源与演化都还不清楚。本文的研究揭示了一个拟南芥中央细胞特化的转录抑制机制，并探讨了十字花科中该机制的起源。

通讯：李红菊 (http://sourcedb.genetics.cas.cn/zw/zjrck/201711/t20171129_4901336.html)

个人简介：2004年，河北师范大学，学士；2010年，遗传发育所，博士。

研究方向： 1. 植物细胞极性建立和极性生长的分子调控机理；2. 植物受精过程中生殖隔离的分子基础。

doi: https://doi.org/10.1073/pnas.1909465117

Journal: PNAS

Published date: March 04, 2020