A morphodynamic study of C. hirsuta leaf development

叶片是种子植物的主要光合器官，其形状变化很大，是了解生物形态发育和多样性的良好模型。然而，叶片形状多样性的形态发生基础尚不清楚。我们的目的是通过比较C. hirsuta和A. thaliana来解决这个问题，C. hirsuta有复杂的叶子解剖成小叶，而A. thaliana有简单的叶子，只有小的锯齿。最近，我们利用遗传学，先进的成像和计算模型来开发一个基于生长的框架，解释这些物种之间的遗传差异如何转化为形式的差异。通过这种方式，我们建立了一个由转录因子cu2、生长素外排转运蛋白pin - formmed1、PIN1和生长素组成的小基因调控网络，这是叶面纹和小叶的迭代模式形成的基础。在这种情况下，由两种不同同源盒基因的物种特异性作用引起的局部生长差异的结合，突出了CUC2模式机制造成的生长差异，并奠定了小叶而不是锯齿形成的基础。我们还发现，与CUC2起冗余作用的CUC2亲缘基因CUC1的调控多样化也有助于这些物种特有的叶片形状差异，并促进毛毛草小叶的形成。在此基础上，我们建议研究ChCUC1如何在上述框架中整合影响叶片形态发生。具体而言，我们将确定ChCUC1如何通过选定的下游基因影响细胞的生长、分化、细胞增殖和生长方向。为了帮助这项研究，我们将使用遗传镶嵌来评估其不同功能的非细胞自主性的程度和基础。我们将继续使用计算方法来综合得到的信息并指导实验。该项目的结果将是(i)澄清CUC1细胞水平作用模式的信息和（ii）基于机械的计算模型，这些模型将CUC1相对于先前描述的调节因子对叶片形状的影响概念化。

Leaves are the main photosynthetic organs of seed plants and show considerable variation in their shape, making them a good model to understand development and diversity of biological forms. However, the morphogenetic basis for leaf shape diversity is poorly understood. We aim to address this question by comparing C. hirsuta which has complex leaves dissected to leaflets and A. thaliana which has simple leaves that bear only small serrations. Recently, we used genetics, advanced imaging and computational modelling to develop a growth-based framework explaining how genetic differences between these species are translated to differences in form. In this way, we established that a small gene regulatory network of the transcription factor CUP-SHAPE COTYLEDONS2 (CUC2), the auxin efflux transporter (PIN-FORMED1) PIN1 and auxin underlies the iterative pattern formation of leaf serrations as well as leaflets. In this context, the combination of local growth differences caused by species-specific action of two different homeobox genes accentuates growth differences created by this CUC2 patterning mechanism and underlies formation of leaflets instead of serrations. We also discovered that regulatory diversification of the CUC2 paralogue CUC1, that acts redundantly with CUC2, also contributes to these species-specific differences of leaf shape and promotes leaflet formation in C. hirsuta. On this basis, we propose to investigate how ChCUC1 is integrated in the above framework to influence leaf morphogenesis. Specifically, we will determine how ChCUC1 acts through selected downstream genes to influence cell growth, differentiation, cell proliferation and growth direction. To aid this investigation, we will use genetic mosaics to evaluate the degree of, and basis for, non-cell autonomy of its diverse functions. We will continue using computational approaches to synthesize the resulting information and guide experiments. The outcome of the project will be (i) information that clarifies the CUC1 cell-level mode of action and (ii) mechanistically grounded computational models that conceptualize the effect of CUC1 on leaf shape relative to previously described regulators.