International Research Fellowship Program: Characterization and Modeling of Higher Order Phyllotaxis in Helianthus

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。国际研究奖学金计划使美国科学家和工程师能够在国外进行9至24个月的研究。该计划的奖项提供了联合研究的机会，并利用国外独特或互补的设施、专业知识和实验条件。该奖项将支持西沃恩·A·布雷布鲁克博士与瑞士伯尔尼大学克里斯托弗·库勒迈尔博士合作的为期24个月的研究奖学金。气生器官的形成主要发生在茎顶端分生组织中，这是一种特殊的干细胞群。位于主茎的顶端。向日葵头状花序(向日葵头状花序)中观察到的高阶叶序具有明显的螺旋模式，这是由于分生组织的精确模式而形成的。在给定的头状花序中，这些螺旋的数目是斐波纳契数列的成员，这可能是头状花序S发育过程中黄金角重复产生的一种新现象。最近的叶序研究工作强调了植物激素生长素在建立螺旋叶序模式和黄金角度重复中的重要作用；然而，所有这些工作都是在番茄和拟南芥中较低级别的叶序中完成的，并涉及不同于大的扁平向日葵头状花序的小圆柱形分生组织。从历史上看，有大量的数学和生物力学工作试图描述向日葵头状结构中看到的高阶模式。这些工作假定分生组织内的机械力也可能是重要的模式生成器或执行者。研究人员正在通过结合生物学、物理学、数学和计算模型的跨学科方法，研究向日葵头状花序发育中化学形成的模式(通过生长素)和机械强制模式之间的相互作用。生长素运输的动力学正在用免疫组织学来研究，以可视化生长素运输蛋白Pin1，它建立了生长素定向流动。向日葵Pin1(HaPIN1)基因已被克隆，并在顶端表达。此外，正在开发工具，将生长素浓度的分子标记引入向日葵植物。随后，在生长素水平和头状叶的机械特性被操纵之后，生长素动态的变化被检测。各种方法被用来破坏小头中的机械力，如显微解剖、激光切割和通过加压施加外力。使用微电子机械系统(MEMS)力传感器收集横跨小头的不同组织硬度的生物力学测量。在上述生长素水平和机械性能的处理之后，也在进行测量。研究人员正在利用描述生长素动力学和组织生物力学之间关系的结果数据来改进和扩展现有的叶序计算模型，以包括向日葵头状结构中看到的高阶模式。这种对一种古老现象的多学科和综合方法，即建立基于费波纳奇模式的自然界，将增加对生物力学和植物生物学领域的理解。它还将有助于增加生物学家和非生物学家之间的科学论述和合作，这本身就是科学领域内紧急适应的一个可能的例子。

0853105BraybrookThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-four-month research fellowship by Dr. Siobhan A. Braybrook to work with Dr. Christopher Kuhlemeir at the University of Bern in Switzerland.Phyllotaxis describes the arrangement of plant organs as they are formed during development. The formation of aerial organs occurs mainly from the shoot apical meristem, a specialized population of ?stem cells? situated at the apex of the main stem. The high order phyllotaxis observed in Helianthus annuus floral heads (sunflower capitulum) displays striking spiral patterns which develop as a result of precise patterning at the meristem. The numbers of these spirals in a given capitulum are members of the Fibonacci series, which is likely an emergent phenomenon resulting from the repetition of the Golden Angle during the capitulum?s development. Recent work in phyllotaxis research has highlighted the important role of the plant hormone auxin in establishing spiral phyllotactic patterns and the repetition of the Golden Angle; however, all of this work has been done with lower order phyllotaxis in tomato and Arabidopsis and involves small cylindrical meristems unlike the large flat sunflower capitulum. Historically there has been a large body of mathematical and biomechanical work attempting to describe the high order patterns seen in sunflower capitula. These works postulate that mechanical forces within the meristem may also be important pattern generators or enforcers. The investigators are examining the interplay between chemically established patterning (via auxin) and mechanically enforced patterning is investigated in the developing sunflower capitulum using an interdisciplinary approach by combining biology, physics, mathematics, and computational modeling. The dynamics of auxin transport are being examined using immunohistollogy to visualize the auxin transport protein PIN1 which establishes directional auxin flow. The gene encoding sunflower PIN1 (HaPIN1) has been cloned and its expression is found in the shoot apex. In addition, tools are being developed to introduce molecular markers for auxin concentration into sunflower plants. Subsequently, changes in auxin dynamics are being examined after manipulation of both auxin levels and mechanical properties of the capitpulum. Various methods are being employed to disrupt mechanical forces in the capitulum such as microdissection, laser abalation, and the imposition of extraneous forces via compression. Biomechanical measurements of differential tissue stiffness across the capitulum are being gathered using a MicroElectroMechanical Systems (MEMS) force sensor. Measurements are also being made after the aforementioned manipulations of auxin levels and mechanical properties. The resulting data describing the relationship between auxin dynamics and tissue biomechanics is being used by the investigators to refine and expand existing computational models of phyllotaxis to include the high order patterns seen in sunflower capitula. This multidisciplinary and integrative approach to an age old phenomenon, the establishment of Fibonacci based patterns in nature, will add understanding to the fields of biomechanics and plant biology. It will also serve to increase scientific discourse and collaboration between biologists and non-biologists, itself a likely example of emergent adaptation within the field of science.