Putting the brakes on pollen wall development: A conserved negative feedback loop regulates pollen exine formation in flowering plants
Putting the brakes on pollen wall development: A conserved negative feedback loop regulates pollen exine formation in flowering plants
复制标题
阻止花粉壁发育：保守的负反馈回路调节开花植物花粉外壁的形成
DOI：
10.1016/j.molp.2023.08.010
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发表时间：
2023
期刊：
影响因子：
27.5
通讯作者：
Dobritsa, Anna A.
中科院分区：
文献类型：
--
作者：
Zhou, Yuan;Dobritsa, Anna A.
花粉粒被一个复杂的多层结构，即花粉壁所覆盖。外壁是细胞壁的最外层，由具有显著物理和化学稳定性的生物聚合物孢粉素组成。在不同的植物中，保护花粉免受恶劣环境胁迫的外壁具有非常不同的形态并形成不同的模式（Wang和Dobritsa，2018）。它还有助于授粉，花粉-柱头相互作用，花粉水合作用和最终的花粉管释放。在雄性减数分裂后，当四个小孢子排列成四分体构型并被胼胝质壁包围时，外壁开始形成（Ariizumi和Toriyama，2011）。在这个阶段，小孢子分泌原孢素，即在小孢子质膜和胼胝质壁之间积累的外壁前体，为外壁图案化提供支架（Wang et al.，2021年）。当胼胝质壁逐渐降解时，附近的绒毡层细胞分泌孢粉素，并沉积在原壁模板上形成成熟的外壁。这一过程需要小孢子与周围绒毡层之间协调活动，绒毡层转录激活因子调控外壁的形成。在拟南芥和水稻中，该级联反应已被研究得最多，分别称为AtDYT1-AtTDF1-AtAMS-AtMS 188/MYB80-AtMS 1（Wang et al.，2018）和OsUDT1-OsTDF1-OsTDR-OsMS188/MYB80-OsPTC 1（Han et al. 2021年）。在这个级联反应中，每个转录因子（TF）诱导下一个TF的表达，并且，共同地，它们激活外壁形成和绒毡层活性所需的基因。虽然这些级联已得到很好的研究，但仍存在一些问题。一个有趣的问题涉及这样的发现，即这些激活剂中的一些的功能丧失突变导致它们自身的转录物和上游作用TF的转录物的水平增加（Ferguson等人，2017年; Yang等人，2019年）。这个矛盾的发现表明，在这个级联中存在一个未知的负反馈调节器。在最近的一项研究中，侯和同事（侯等人，2023年）揭开了这个谜题之前缺失的一块。在一项tour-de-force研究中，他们确定了绒毡层级联反应的阻遏物，并表明它创造了一个保守的负反馈回路，调节开花植物中及时的绒毡层退化和精确的外壁形成。
Pollen grains are covered by a complex multi-layered structure, the pollen wall. Exine, the outermost layer of this wall, is made from the biopolymer sporopollenin that exhibits remarkable physical and chemical stability. In different plants, exine, which shields pollen from harsh environmental stresses, has very diverse morphologies and forms different patterns (Wang and Dobritsa, 2018). It also contributes to pollination, pollen–stigma interaction, pollen hydration, and eventual release of the pollen tube. Formation of exine begins after male meiosis when four microspores are arranged in a tetrad configuration and enclosed by the callose wall (Ariizumi and Toriyama, 2011). At this stage, microspores secrete primexine, the precursor of exine that accumulates between the microspore plasma membrane and the callose wall, providing a scaffold for exine patterning (Wang et al., 2021). As the callose wall gradually gets degraded, sporopollenin is secreted by the nearby tapetal cells and deposited onto the primexine template to form mature exine. This process requires coordination of activities between microspores and the surrounding tapetum.Exine formation is controlled by the regulatory cascade of tapetal transcriptional activators. In Arabidopsis and rice, where this cascade has been the most studied, it is respectively referred to as AtDYT1-AtTDF1-AtAMS-AtMS188/MYB80-AtMS1 (Wang et al., 2018) and OsUDT1-OsTDF1-OsTDR-OsMS188/MYB80-OsPTC1 (Han et al., 2021). In this cascade, each transcription factor (TF) induces the expression of the next TF, and, collectively, they activate genes required for exine formation and tapetal activity. Although these cascades have been well studied, some questions remain. One intriguing question concerns the discovery that loss-of-function mutations in some of these activators lead to increased levels of their own transcripts and those of the upstream-acting TFs (Ferguson et al., 2017; Yang et al., 2019). This paradoxical finding suggested the presence within this cascade of an unknown negative-feedback regulator. In a recent study, Hou and colleagues (Hou et al., 2023) have unveiled a previously missing piece of this puzzle. In a tour-de-force study, they identified a repressor of the tapetal cascade and showed that it creates a conserved negative feedback loop that regulates timely tapetal degeneration and precise exine formation in flowering plants.