A possible involvement of autophagy in amyloplast degradation in columella cells during hydrotropic response of Arabidopsis roots
A possible involvement of autophagy in amyloplast degradation in columella cells during hydrotropic response of Arabidopsis roots
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DOI：
10.1007/s00425-012-1655-5
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发表时间：
2012-10-01
期刊：
影响因子：
4.3
通讯作者：
Takahashi, Hideyuki
中科院分区：
文献类型：
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作者：
Nakayama, Mayumi;Kaneko, Yasuko;Takahashi, Hideyuki
幼苗的根不仅表现出向重力性，而且表现出向水性，而且这两种向性相互干扰。在拟南芥（Arabidopsis thaliana）根中，在向水反应过程中，柱细胞中的造粉体迅速降解。淀粉体的降解参与重力感应，通过降低向重力反应增强了向水性反应。然而，淀粉体在向水性反应根中降解的机制仍然未知。在这项研究中，淀粉体在柱细胞在向水反应过程中的降解机制方面进行了研究，通过分析细胞器形态，细胞极性和基因表达的变化。结果表明，促水刺激或系统性水分胁迫可引起柱细胞内细胞器形态和定位的显著变化。具体而言，向水性响应或水分胁迫根的柱状细胞失去极性的内质网（ER）的分布，并显示加速空泡化和核运动。ER定位的GFP分析表明，ER重新分布在发达的液泡周围。细胞内常出现自噬体样结构的淀粉体分解。无论是水溶性刺激和水分胁迫上调AtATG 18 a的表达，这是所需的自噬体的形成。此外，用GFP-AtATG 8a分析揭示，水溶性刺激和水分胁迫都诱导了柱细胞中自噬体的形成。此外，质体标记，pt-GFP，在小柱细胞的表达显着下降，响应水溶性刺激和水分胁迫，但其减少少得多的自噬突变体atg 5。这些结果表明，水溶性刺激赋予水分胁迫的根，这引发了自噬反应负责的淀粉体的降解柱细胞的拟南芥根。
Seedling roots display not only gravitropism but also hydrotropism, and the two tropisms interfere with one another. In Arabidopsis (Arabidopsis thaliana) roots, amyloplasts in columella cells are rapidly degraded during the hydrotropic response. Degradation of amyloplasts involved in gravisensing enhances the hydrotropic response by reducing the gravitropic response. However, the mechanism by which amyloplasts are degraded in hydrotropically responding roots remains unknown. In this study, the mechanistic aspects of the degradation of amyloplasts in columella cells during hydrotropic response were investigated by analyzing organellar morphology, cell polarity and changes in gene expression. The results showed that hydrotropic stimulation or systemic water stress caused dramatic changes in organellar form and positioning in columella cells. Specifically, the columella cells of hydrotropically responding or water-stressed roots lost polarity in the distribution of the endoplasmic reticulum (ER), and showed accelerated vacuolization and nuclear movement. Analysis of ER-localized GFP showed that ER redistributed around the developed vacuoles. Cells often showed decomposing amyloplasts in autophagosome-like structures. Both hydrotropic stimulation and water stress upregulated the expression of AtATG18a, which is required for autophagosome formation. Furthermore, analysis with GFP-AtATG8a revealed that both hydrotropic stimulation and water stress induced the formation of autophagosomes in the columella cells. In addition, expression of plastid marker, pt-GFP, in the columella cells dramatically decreased in response to both hydrotropic stimulation and water stress, but its decrease was much less in the autophagy mutant atg5. These results suggest that hydrotropic stimulation confers water stress in the roots, which triggers an autophagic response responsible for the degradation of amyloplasts in columella cells of Arabidopsis roots.