Dorcey Eavan, Urbez Cristina, Blázquez Miguel A, Carbonell Juan, Perez-Amador Miguel A
Instituto de Biología Molecular y Celular de Plantas (IBMCP), Consejo Superior de Investigaciones Científicas, Universidad Politécnica de Valencia (CSIC-UPV), Avenida de los naranjos s/n, 46022 Valencia, Spain.
Plant J. 2009 Apr;58(2):318-32. doi: 10.1111/j.1365-313X.2008.03781.x. Epub 2008 Dec 16.
Fruit development is usually triggered by ovule fertilization, and it requires coordination between seed development and the growth and differentiation of the ovary to host the seeds. Hormones are known to synchronize these two processes, but the role of each hormone, and the mechanism by which they interact, are still unknown. Here we show that auxin and gibberellins (GAs) act in a hierarchical scheme. The synthetic reporter construct DR5:GFP showed that fertilization triggered an increase in auxin response in the ovules, which could be mimicked by blocking polar auxin transport. As the application of GAs did not affect auxin response, the most likely sequence of events after fertilization involves auxin-mediated activation of GA synthesis. We have confirmed this, and have shown that GA biosynthesis upon fertilization is localized specifically in the fertilized ovules. Furthermore, auxin treatment caused changes in the expression of GA biosynthetic genes similar to those triggered by fertilization, and also restricted to the ovules. Finally, GA signaling was activated in ovules and valves, as shown by the rapid downregulation of the fusion protein RGA-GFP after pollination and auxin treatment. Taken together, this evidence suggests a model in which fertilization would trigger an auxin-mediated promotion of GA synthesis specifically in the ovule. The GAs synthesized in the ovules would be then transported to the valves to promote GA signaling and thus coordinate growth of the silique.
果实发育通常由胚珠受精触发，它需要种子发育与子房的生长和分化之间相互协调，以便容纳种子。已知激素可使这两个过程同步，但每种激素的作用以及它们相互作用的机制仍不清楚。在这里，我们表明生长素和赤霉素（GAs）以一种分级模式起作用。合成报告构建体DR5:GFP显示，受精触发了胚珠中生长素反应的增加，这可以通过阻断生长素极性运输来模拟。由于施用赤霉素不影响生长素反应，受精后最可能的事件顺序涉及生长素介导的赤霉素合成激活。我们已经证实了这一点，并表明受精后的赤霉素生物合成特异性地定位于受精的胚珠中。此外，生长素处理导致赤霉素生物合成基因的表达发生变化，类似于受精触发的变化，并且也仅限于胚珠。最后，如授粉和生长素处理后融合蛋白RGA-GFP的快速下调所示，胚珠和瓣膜中的赤霉素信号被激活。综上所述，这些证据表明了一个模型，即受精会触发生长素介导的赤霉素合成在胚珠中的特异性促进。然后，在胚珠中合成的赤霉素将被运输到瓣膜以促进赤霉素信号传导，从而协调整个角果的生长。
