Targeting of pollen tubes to ovules is dependent on nitric oxide (NO) signaling
Targeting of pollen tubes to ovules is dependent on nitric oxide (NO) signaling
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DOI：
10.1093/mp/ssn034
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发表时间：
2008-07-01
期刊：
影响因子：
27.5
通讯作者：
Feijo, Jose A.
中科院分区：
文献类型：
--
作者：
Prado, Ana Margarida;Colaco, Renato;Feijo, Jose A.
在很大程度上，驱动花粉管在雌蕊内导航和珠孔靶向的引导信号仍然未知。以往的体外研究表明，一氧化氮(NO)对百合(Lilium Long Giflorum)花粉管的生长起负趋化作用。此外，拟南芥Atnos1突变株表现出有缺陷的NO产生，降低了育性。在此，我们利用拟南芥体内和百合半活体实验，重点研究了NO在花粉-雌蕊交流过程中的作用。野生型和Atnos1植物的异花授粉表明，该突变以一种与异常花粉管引导相一致的方式影响雌蕊组织。此外，DAF-2DA对Kanadi花突变体中NO的染色表明，在珠孔周围的不对称限制性区域中存在NO。花粉-雌蕊相互作用转录组表明AtNOS1和两个硝酸还原酶(Nr1和nr2)的转录本具有时程特异性调节，它们共同被认为触发了一条可能的NO信号通路。用分离的胚珠和百合花粉进行的半活体分析进一步表明，NO是珠孔靶向发生所必需的。这一证据得到了CPTiO处理的支持，随后在面向胚珠的花粉管中形成了气球尖端。激活花粉管中的钙内流部分挽救了正常的花粉管形态，表明这一途径也依赖于钙信号。通过直接成像NO诱导的重定向过程中细胞内游离钙浓度，进一步证实了NO在调节钙信号中的作用，其中钙离子出现两个峰值-一个在减慢/停止反应期间，第二个峰值在重定向和生长恢复期间。综上所述，这些结果为NO信号事件在花粉-雌蕊相互作用中的参与提供了证据。尤其重要的是，NO似乎通过调节其扩散因子的作用，直接影响了花粉管对胚珠珠孔的定向作用。
The guidance signals that drive pollen tube navigation inside the pistil and micropyle targeting are still, to a great extent, unknown. Previous studies in vitro showed that nitric oxide (NO) works as a negative chemotropic cue for pollen tube growth in lily (Lilium longiflorum). Furthermore, Arabidopsis thaliana Atnos1 mutant plants, which show defective NO production, have reduced fertility. Here, we focus in the role of NO in the process of pollen-pistil communication, using Arabidopsis in-vivo and lily semi-vivo assays. Cross-pollination between wild-type and Atnos1 plants shows that the mutation affects the pistil tissues in a way that is compatible with abnormal pollen tube guidance. Moreover, DAF-2DA staining for NO in kanadi floral mutants showed the presence of NO in an asymmetric restricted area around the micropyle. The pollen-pistil interaction transcriptome indicates a time-course-specific modulation of transcripts of AtNOS1 and two Nitrate Reductases (nr1 and nr2), which collectively are thought to trigger a putative NO signaling pathway. Semi-vivo assays with isolated ovules and lily pollen further showed that NO is necessary for micropyle targeting to occur. This evidence is supported by CPTIO treatment with subsequent formation of balloon tips in pollen tubes facing ovules. Activation of calcium influx in pollen tubes partially rescued normal pollen tube morphology, suggesting that this pathway is also dependent on Ca2+ signaling. A role of NO in modulating Ca2+ signaling was further substantiated by direct imaging the cytosolic free Ca2+ concentration during NO-induced re-orientation, where two peaks of Ca2+ occur-one during the slowdown/stop response, the second during re-orientation and growth resumption. Taken together, these results provide evidence for the participation of NO signaling events during pollen-pistil interaction. Of special relevance, NO seems to directly affect the targeting of pollen tubes to the ovule's micropyle by modulating the action of its diffusible factors.