A Ploidy-Sensitive Mechanism Regulates Aperture Formation on the Arabidopsis Pollen Surface and Guides Localization of the Aperture Factor INP1.
A Ploidy-Sensitive Mechanism Regulates Aperture Formation on the Arabidopsis Pollen Surface and Guides Localization of the Aperture Factor INP1.
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DOI：
10.1371/journal.pgen.1006060
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发表时间：
2016-05
期刊：
影响因子：
4.5
通讯作者：
Dobritsa AA
中科院分区：
文献类型：
--
作者：
Reeder SH;Lee BH;Fox R;Dobritsa AA
花粉为研究胞外结构的精确形成和沉积机制提供了一个强有力的模型。花粉壁外壁的沉积导致花粉表面产生物种特有的图案。在大多数物种中，外壁在花粉表面不均匀发育，导致外壁形成孔洞，这些孔洞在数量、形态和位置上都是物种特有的。很久以前，就有人提出孔的数量和位置可能由小孢子四分体的几何形状和姐妹小孢子之间最后接触点的数量决定。小孢子四分体是减数分裂产生花粉粒的前体。我们通过表征具有异位孔和/或减数分裂产物异常几何形状的拟南芥突变体来测试该模型。在这里，我们证明接触点本身并不作为孔径数量的决定因素，并且四分体的正确几何构象既不是必要的，也不是充分的，以产生正确的孔径数量。然而，花粉倍性敏感的机制对气孔数量和位置以及引导气孔因子INP1走向未来的气孔位置非常重要。在具有异位孔的突变体中，INP1定位位点的数量和位置取决于倍性或与倍性相关的细胞大小，而不是INP1水平，这表明在INP1进入它们之前，已经指定了形成孔的位点。细胞外物质在细胞旁的沉积可以保护细胞，改变其形态，或帮助细胞移动和交流。为了能够完成这样的功能，细胞外的物质必须非常精确地沉积，但是细胞是如何达到这种精度的大部分是未知的。一个非常精确沉积的胞外结构的美丽例子是花粉粒周围的壁。不同种类的花粉通常看起来非常不同，部分原因是花粉表面的某些地方有壁物质沉积，而其他地方没有。没有壁的地方被称为孔洞，它们在形状、数量和位置上都是物种特有的。这表明，发育中的花粉始终将其表面的某些区域标记为与表面的其他区域不同，从而使它们能够发育成孔。裂孔的数目和位置长期以来被认为是由减数分裂过程中产生的花粉前体的几何排列和这些细胞之间最后接触点的数量决定的。在这里，我们通过使用具有减数分裂产物异常排列或最后接触点数量的拟南芥突变体来挑战这一模型，并证明这些因素对于孔放置既不是必要的也不是充分的。相反，我们发现花粉倍性敏感的机制——细胞对依赖于倍性本身或细胞大小的因子的反应——对孔数和位置非常重要。
Pollen presents a powerful model for studying mechanisms of precise formation and deposition of extracellular structures. Deposition of the pollen wall exine leads to the generation of species-specific patterns on pollen surface. In most species, exine does not develop uniformly across the pollen surface, resulting in the formation of apertures–openings in the exine that are species-specific in number, morphology and location. A long time ago, it was proposed that number and positions of apertures might be determined by the geometry of tetrads of microspores–the precursors of pollen grains arising via meiotic cytokinesis, and by the number of last-contact points between sister microspores. We have tested this model by characterizing Arabidopsis mutants with ectopic apertures and/or abnormal geometry of meiotic products. Here we demonstrate that contact points per se do not act as aperture number determinants and that a correct geometric conformation of a tetrad is neither necessary nor sufficient to generate a correct number of apertures. A mechanism sensitive to pollen ploidy, however, is very important for aperture number and positions and for guiding the aperture factor INP1 to future aperture sites. In the mutants with ectopic apertures, the number and positions of INP1 localization sites change depending on ploidy or ploidy-related cell size and not on INP1 levels, suggesting that sites for aperture formation are specified before INP1 is brought to them. Deposition of extracellular materials next to a cell can protect the cell, change its morphology, or help it to move and communicate. To be able to perform such functions, extracellular materials must be deposited very precisely, but how cells achieve such precision is mostly unknown. A beautiful example of a very precisely deposited extracellular structure is the wall surrounding pollen grains. Pollen from different species often looks remarkably different–in part, because wall materials are deposited at some places on pollen surface and absent from others. The places where the wall is absent are called apertures and they are species-specific in shape, number, and positions. This suggests that developing pollen consistently marks some of its surface regions as different from the rest of the surface to allow them to develop into apertures. Aperture number and positions were long thought to be determined by geometric arrangement of pollen precursors arising during meiotic division and by the number of last-contact points between these cells. Here we challenge this model by using Arabidopsis mutants with abnormal arrangement of meiotic products or the number of last-contact points and by demonstrating that these factors are neither necessary nor sufficient for aperture placement. In contrast, we find that a mechanism sensitive to pollen ploidy–with cells responding to factors dependent either on ploidy itself or on cell size–is very important for aperture number and positions.