Elucidating the Gene Networks Controlling Branch Angle and the Directional Growth of Lateral Meristems in Trees

Trees can adopt a wide variety of architectural forms. Architectural plasticity plays important roles in forest ecosystems, agriculture, and landscape aesthetics. Tree architecture is a consequence of numerous developmental traits that include branching pattern, branch number, branch length, and branch angle. These traits are largely a function of two key developmental processes: apical dominance and apical control. Apical dominance is a well understood process that inhibits lateral bud outgrowth through signals emanating from the shoot apex. Intensive studies have revealed the signals and the underlying molecular mechanisms that operate in herbaceous plants such as Arabidopsis and pea. In contrast, apical control is the process by which the apex influences the overall tree structure upon successive years of growth and development in woody species. Although some progress has been made from a physiological perspective, the genetic and molecular mechanisms of apical control are largely unknown. The overarching goal of the project is to develop detailed knowledge about how trees adopt specific architectural forms, specifically with regard to apical control of the lateral branch angle and directional growth. Using a combination of genome-scale studies to elucidate key gene networks and molecular pathways coupled with innovative whole tree imaging technologies that will enable non-destructive structural phenotyping, the project will address the following questions: 1) What gene expression networks differentiate the shoot apical meristem from lateral meristems? What changes take place when a lateral shoot meristem transitions to becoming the apical meristem? How are these expression networks altered in branch angle mutants including pillar/columnar tree forms and weeping types? 2) What is the genetic and molecular basis for these mutant tree forms in peach and apple? What are the identities of the mutated genes? 3) With regard to the identified genes, what protein-protein interaction networks are they associated with? Through which pathways do they exert their effects on tree form?

树木可具有多种多样的构型形态。构型可塑性在森林生态系统、农业及景观美学领域发挥着关键作用。
树木构型由众多发育性状共同决定，这些性状涵盖分枝模式、分枝数量、分枝长度与分枝角度。这些性状在很大程度上受两个关键发育过程调控：顶端优势（apical dominance）与顶端控制（apical control）。
顶端优势是一种已被充分阐明的生物学过程，它通过茎尖（shoot apex）释放的信号抑制侧芽萌发。针对拟南芥（Arabidopsis）与豌豆（pea）等草本植物的深入研究，已阐明了其中发挥作用的信号通路与潜在分子机制。与之相对，顶端控制（apical control）是指木本植物经过多年连续生长发育后，茎尖对整体树木构型产生调控作用的过程。尽管目前已从生理学视角取得了一定进展，但顶端控制的遗传与分子机制在很大程度上仍未明确。
本项目的总体目标是深入解析树木形成特定构型的机制，特别是针对侧枝角度与定向生长的顶端控制过程。本项目将结合全基因组尺度研究以阐明关键基因调控网络与分子通路，并辅以创新性的整树成像技术，实现无损式结构表型分型（non-destructive structural phenotyping），从而解决以下问题：
1） 区分茎尖分生组织（shoot apical meristem）与侧生分生组织的基因表达网络有哪些？当侧生茎尖分生组织转变为顶端分生组织时，会发生哪些变化？在包括柱状（pillar/columnar）树形与垂枝（weeping）类型在内的分枝角度突变体中，这些表达网络发生了哪些改变？
2） 桃（peach）与苹果（apple）中这些突变树形的遗传与分子基础是什么？已发生突变的基因的具体信息是什么？
3） 针对已鉴定出的基因，它们与哪些蛋白质相互作用网络相关？它们通过哪些通路对树木构型产生调控作用？