Role of phloem-mobile sucrose and auxin in the development of the root system

植物生长依赖于茎尖、叶缘和根尖处聚集的干细胞的活性，以及静止并等待激活的干细胞簇。 这些所谓的分生组织的活性决定了植物是否高而分枝少、矮而浓密等。同样，根系的结构由主根和侧根顶端的分生组织的活性以及这些分生组织在根原基中的初始激活决定。 重要的是，植物的许多分生组织的活动是协调的，以产生一种植物，其形态是优化其栖息地。 事实上，根和芽系统的生长是协调的，但这种协调是如何发生的知之甚少。 以前的研究清楚地表明，在生理范围内人工增加叶片中的蔗糖显著地刺激侧根的形成，这表明通常由叶片通过光合作用产生的蔗糖调节根系发育。 这意味着一个长距离的机制，沟通的地上组织的蔗糖状态的根系。 蔗糖通过韧皮部从地上部移动到根系，在韧皮部处，基于陡峭的浓度梯度，蔗糖在根分生组织处卸载。 有趣的是，植物激素生长素也在叶片中产生，并通过韧皮部转移到根系，该项目将研究来自气生组织的光合作用如何驱动韧皮部分配到根分生组织，提供生长素，从而调节其活性。 该项目将使用转基因植物，改变水平的蔗糖和生长素转移到韧皮部，连同荧光染料，允许直接可视化韧皮部的运动和交付，以测试这个模型。 如果成功，该项目的结果将1）证明韧皮部在不同位置整合植物器官发育; 2）确定韧皮部中携带的分子信号。 这将是极少数的例子之一，在整个植物的协调发展是机械地理解在生理和分子水平。 该项目的更广泛影响包括培训各级学生和向社区推广科学。

Plant growth relies on the activity of stem cells clustered at shoot tips, leaf margins, and root tips, and also stem cell clusters that are quiescent and await activation. The activity of these so-called meristems determines whether plants are tall with few branches, short and bushy, etc. Similarly, the architecture of the root system is determined by the activity of meristems at the tips of primary and lateral roots, and the initial activation of these meristems in root primordia. It is essential that the activity of the plant's many meristems is coordinated to produce a plant whose morphology is optimized for its habitat. Indeed, root and shoot system growth is known to be coordinated, but how this coordination occurs is poorly understood. Previous studies clearly demonstrated that artificially increasing sucrose within a physiological range in the leaves dramatically stimulates lateral root formation, suggesting that the sucrose normally produced by leaves through photosynthesis is regulating root system development. This implicates a long distance mechanism that communicates the sucrose status of the aerial tissues to the root system. Sucrose moves from shoot to root system via the phloem, where it is unloaded at root meristems based on the steep concentration gradient. Interestingly, the plant hormone auxin is also produced in the leaves and moved to the root system via the phloem, This project will investigate how photosynthate from aerial tissues drives phloem allocation to root meristems, delivering auxin and thereby regulating their activity. This project will use transgenic plants that alter the levels of sucrose and auxin translocated in the phloem, together with fluorescent dyes that allow direct visualization of phloem movement and delivery, to test this model. If successful, the results from this project will 1) demonstrate that phloem acts to integrate plant organ development at different locations; and 2) determine the molecular signal that is carried in the phloem. This would be one of very few examples in which coordinated development in the whole-plant is understood mechanistically at the physiological and molecular levels. The broader impacts of this project include training of students at all levels and scientific outreach to the community.