Regulation of Auxin Fluxes Required for Phototropic Growth

植物依靠阳光进行光合作用，并调整自己的生长以优化光捕捉。向光性，即生长朝向光线的重新定向，代表了这些重要的适应性反应之一。现代对向光性的研究始于查尔斯·达尔文对单子叶草类植物的实验，最终导致了植物生长激素生长素的发现，建立了这样一个概念，即对枝梢顶端的光感知会触发下面组织的差异弯曲。在过去的二十年里，对模式植物拟南芥的分子遗传分析已经确定了向光性的主要光受体PHI1，以及主要的生长素转运蛋白。然而，尽管进行了广泛的努力，但光感受器如何调节生长素运输以建立差异生长仍然知之甚少，这一过程在单子叶植物和双子叶植物之间是否保守也是如此。因此，这一建议的主要目的是识别和描述与建立生长素通量相关的信号事件，这些生长素通量是光亲生长所需的。通过采用一种改进的方法来研究拟南芥在没有通常与幼苗光形态建成相关的发育事件的情况下的向光性，我们已经表明，单子叶植物和双子叶植物之间的光感知和差异生长的接近是保守的：在这两种植物类型中，差异生长是生长素横跨茎尖侧向运动的结果。此外，我们还鉴定了两种生长素转运蛋白，PIN形成的(PIN3)和ATP结合盒B19(ABCB19)，它们参与了这些运动，后者直接受Pho1的调节，并为侧向生长素在顶端的运输提供了基础。这些发现揭示了光接收和生长素信号耦合事件的新机制信息，这两个过程对塑造植物生长至关重要。因此，这项提议的重点是进一步表征建立光致生长所涉及的分子过程。鉴于光和生长素在控制植物发育中的基本重要性，这些见解最终应该为操纵植物生长以获得农艺收益提供新的策略。

Plants depend on sunlight for photosynthesis and adapt their growth to optimise light capture. Phototropism, the reorientation of growth towards light, represents one of these important adaptive responses. Modern-day studies of phototropism began with experiments in monocotyledonous grasses by Charles Darwin and led ultimately to the discovery of the plant growth hormone auxin, establishing the concept that light perception at the shoot apex triggers differential bending in the tissues below. In the past two decades, molecular-genetic analysis in the model flowering plant Arabidopsis thaliana has identified the principle photoreceptor for phototropism, phot1, as well as the major auxin transporters. Despite extensive efforts, however, how the photoreceptor regulates auxin transport so as to establish differential growth is poorly understood, as is whether this process is conserved between monocots and dicots. Therefore, the key aim of this proposal is to identify and characterise the signalling events associated with establishing auxin fluxes required for phototropic growth. By adopting a revised approach to study phototropism in Arabidopsis in the absence of developmental events that are typically associated with seedling photomorphogenesis, we have shown that the proximity of light perception and differential growth is conserved between monocots and dicots: in both plant types, differential growth is a consequence of lateral auxin movements across the shoot apex. Moreover, we have identified two auxin transporter proteins, PIN-FORMED (PIN3) and ATP-BINDING CASSETTE B19 (ABCB19), that contribute to these movements, the latter of which is directly regulated by phot1 and serves to prime lateral auxin fluxes in the shoot apex. These findings uncover new mechanistic information of the events coupling photoreception and auxin signalling, two processes that are critical for shaping plant growth. Hence, this proposal is focused on further characterising the molecular processes involved in establishing phototropic growth. Given the fundamental importance of both light and auxin in controlling plant development, these insights should ultimately provide new strategies to manipulate plant growth for agronomic gain.