A WRKY transcription factor recruits the SYG1-like protein SHB1 to activate gene expression and seed cavity enlargement.
A WRKY transcription factor recruits the SYG1-like protein SHB1 to activate gene expression and seed cavity enlargement.
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DOI：
10.1371/journal.pgen.1003347
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发表时间：
2013
期刊：
影响因子：
4.5
通讯作者：
Ni M
中科院分区：
文献类型：
--
作者：
Kang X;Li W;Zhou Y;Ni M
拟南芥和许多菊科植物的种子发育包括胚乳的早期增殖，形成一个接近成熟种子大小的大胚囊或种腔，然后是胚胎生长并取代胚乳的第二阶段。BLUE1下的短下胚轴（SHB1）是真菌、秀丽隐杆线虫、苍蝇和哺乳动物中SYG1蛋白家族的成员。SHB1的功能获得促进胚乳增殖，增大种子大小，上调WRKY转录因子基因minieed3 （MINI3）和LRR受体激酶基因HAIKU2 （IKU2）的表达。IKU2或MINI3的突变都会延缓胚乳增殖并减小种子大小。然而，种子腔形成的分子机制和种子大小在很大程度上仍然未知。在这里，我们发现MINI3和IKU2的表达在受精前和授粉后4天（DAP）被抑制，但在种子腔形成前的2至4 DAP被SHB1激活。SHB1与它们的启动子结合，但没有可识别的DNA结合基序，这种结合在mini3突变体中被消除。MINI3与w -box结合，并将SHB1招募到其自身和IKU2启动子中。有趣的是，SHB1而不是MINI3激活pMINI3::GUS或pIKU2::GUS的转录。我们通过SHB1激活MINI3表达揭示了一个关键的发育开关。MINI3将SHB1招募到其自身和IKU2启动子上，代表了一种新的两步扩增，以对抗IKU2的低表达水平，IKU2是胚乳增殖和种腔扩大的触发因素。在许多双子叶植物中，种子发育的特点是胚乳的快速增殖和被皮的生长，形成一个大的胚囊或种腔。在拟南芥中，种子腔在球形阶段或授粉后4天产生。胚胎随后的生长在第二阶段取代胚乳。因此，初始种子腔的体积与最终种子的大小密切相关。在SHB1 - d中，由于SHB1上调MINI3和IKU2的表达，在4dap时产生了更大的种腔。我们报道了MINI3和IKU2的表达与种腔的形成一致。SHB1通过MINI3锚定在这些启动子上，以w -box依赖的方式激活它们的表达。基因表达的时空调控是控制许多生物胚胎发育的重要机制。SHB1与MINI3的这种相互作用应该会影响它们在包括人类在内的许多其他生物中的同源物的研究。大豆和油菜等主要种子作物的种子发育遵循与拟南芥非常相似的路径。我们的研究结果将导致农业产量的增加，并伴随着每粒种子蛋白质和油含量的增加。
Seed development in Arabidopsis and in many dicots involves an early proliferation of the endosperm to form a large embryo sac or seed cavity close to the size of the mature seed, followed by a second phase during which the embryo grows and replaces the endosperm. SHORT HYPOCOTYL UNDER BLUE1 (SHB1) is a member of the SYG1 protein family in fungi, Caenorhabditis elegans, flies, and mammals. SHB1 gain-of-function enhances endosperm proliferation, increases seed size, and up-regulates the expression of the WRKY transcription factor gene MINISEED3 (MINI3) and the LRR receptor kinase gene HAIKU2 (IKU2). Mutations in either IKU2 or MINI3 retard endosperm proliferation and reduce seed size. However, the molecular mechanisms underlying the establishment of the seed cavity and hence the seed size remain largely unknown. Here, we show that the expression of MINI3 and IKU2 is repressed before fertilization and after 4 days after pollination (DAP), but is activated by SHB1 from 2 to 4 DAP prior to the formation of the seed cavity. SHB1 associates with their promoters but without a recognizable DNA binding motif, and this association is abolished in mini3 mutant. MINI3 binds to W-boxes in, and recruits SHB1 to, its own and IKU2 promoters. Interestingly, SHB1, but not MINI3, activates transcription of pMINI3::GUS or pIKU2::GUS. We reveal a critical developmental switch through the activation of MINI3 expression by SHB1. The recruitment of SHB1 by MINI3 to its own and IKU2 promoters represents a novel two-step amplification to counter the low expression level of IKU2, which is a trigger for endosperm proliferation and seed cavity enlargement. Seed development in many dicots is characterized by a rapid proliferation of the endosperm and growth of integument to form a large embryo sac or seed cavity. In Arabidopsis, the seed cavity is generated at the globular stage or 4 days after pollination. The subsequent growth of the embryo replaces the endosperm during the second phase. Therefore, the volume of the initial seed cavity correlates closely with the final seed size. In shb1-D, an even larger seed cavity is created at 4 DAP due to an up-regulated expression of MINI3 and IKU2 by SHB1. We report that the expression of MINI3 and IKU2 coincides with the formation of the seed cavity. SHB1 is anchored to these promoters by MINI3 to activate their expression in a W-box-dependent manner. Spatiotemporal regulation of gene expression is a crucial mechanism that controls embryo development in many organisms. This interaction of SHB1 with MINI3 should impact studies of their homologs in many other organisms, including humans. Seed development in major seed crops, such as soybean and canola, follows a very similar path to that of Arabidopsis. Our results should lead to an increase in agricultural yields and concomitant increases in the proteins and oil content per seed.
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