Collaborative Research: Ligule development in the proximal-distal axis of the maize leaf

植物构型的改变在作物驯化过程中一直是至关重要的。通过几代人的育种来增加产量，作物植物已经被选择用于改变分枝的数量、长度或角度的各种分枝模式。在玉米中，叶角是一个重要的分枝性状，可能有助于提高玉米产量。叶的角度由叶舌区域决定，叶舌区域形成在叶片和叶鞘之间的边界处。叶片向后倾斜以吸收来自太阳的能量，而鞘紧紧地抓住茎。叶片和叶鞘之间的角度是一种可遗传的性状，可以通过选择进行修改：减小角度使植物更加直立，以获得更紧凑的田地，而增大角度则优化叶片的表面积，以捕获更多能量。因此，了解建立叶角的基本分子机制将为操纵玉米结构提供新的工具。该项目旨在阐明决定叶舌区域何时以及如何形成的复杂因素网络。该项目将首先确定和表征在发育的最早阶段定义叶舌边界的基因的表达。分子，遗传和基因组的方法，然后将用于研究如何叶舌区域的形式。研究结果将与包括育种者、科学界和学生在内的各种受众分享。为此，将制作YouTube视频，向普通观众介绍玉米发育科学，并为学生课堂制作额外的教育材料。所有资源都将通过实验室网站和玉米社区网站（http：//www.example.com）提供。www.maizegdb.org 本计画探讨在未分化的叶原基中，舌区是如何建立为一个明确的器官边界。先前的工作使用解剖学上不同的叶舌作为转录组分析的位点：前叶舌、前叶片和鞘前细胞被清楚地识别用于激光捕获，然后进行RNA测序。由于捕获的特异性，鉴定了在叶舌区域中独特且差异表达的候选基因的集合。在其他器官的边界共享的表达模式表明，叶舌重申发生在拍摄顶端分生组织和雄穗分支边界的侧部器官的启动程序。因此，假设明显不同的器官边界共享基因，并使用共同的机制来定义和限制发育途径。为了验证这一假设，将建立基因网络的早期阶段的叶舌发育和叶舌启动机制进一步研究。第一个具体的目标是确定最早的叶舌形成的决定因素，通过捕获细胞从最年轻的叶原基。候选基因将根据其在其他舌特异性突变体中的表达进行优先排序。第二个目标是研究三个有前途的候选基因通路，支持KNOTTED 1（KN 1）样同源框转录因子和伴侣蛋白在建立叶舌边界的作用。突变体将在这些基因的叶舌和分支表型进行分析。 第三个目的是检验bZIP转录因子LIGULELESS 2（LG 2）与KN 1结合参与定位叶片/鞘边界的假设。蛋白质伴侣将被确定为下游靶标，以确定LG 2在建立叶鞘边界中的作用。

Alteration in plant architecture has been critically important during crop domestication. Through generations of breeding to increase yield, crop plants have been selected for a variety of branching patterns that change the number, length or angle of branches. In maize, leaf angle has been an important branching trait that has likely contributed to increasing corn yields. The angle of the leaf is determined by the ligule region, which forms at the boundary between the blade and sheath. The blade tilts back to absorb energy from the sun while the sheath holds tight to the stem. This angle between the blade and sheath is a heritable trait that can be modified through selection: decreased angle makes plants more upright for more compact fields, whereas increased angle optimizes the surface area of the blade for more energy capture. Thus, understanding the basic molecular mechanisms involved in establishing the leaf angle will provide new tools for manipulating maize architecture. This project aims to clarify the complex network of factors that determine when and how the ligule region forms. This project will first identify and characterize the expression of genes that define the ligule boundary during the earliest stages of development. Molecular, genetic and genomic methods will then be used to investigate how the ligule region forms. The results will be shared with diverse audiences including breeders, the scientific community and with students. To that end, YouTube videos will be produced that describe the science of corn development to a general audience and additional educational materials will be generated for student classrooms. All resources will be made publically available through lab websites and the maize community website (http://www.maizegdb.org). This project investigates how the ligular region is established as a defined organ boundary in the undifferentiated leaf primordium. Previous work used the anatomically distinct ligule as a site for transcriptome analysis: preligule, preblade and presheath cells were clearly identified for laser capture followed by RNA sequencing. Due to the specificity of capture, a collection of candidate genes was identified that is uniquely and differentially expressed in the ligule region. Shared expression patterns in other organ boundaries suggest that the ligule reiterates the lateral organ initiation program that occurs at the shoot apical meristem and at tassel branch boundaries. Thus, distinctly different organ boundaries are hypothesized to share genes and use common mechanisms to define and restrict developmental pathways. To test this hypothesis, gene networks will be established for early stages of ligule development and mechanisms of ligule initiation further investigated. The first specific aim is to identify the earliest determinants of ligule formation by capturing cells from the youngest accessible leaf primordia. Candidate genes will be prioritized based on their expression in other ligule-specific mutants. The second aim investigates three promising candidate gene pathways that support the role of KNOTTED1 (KN1)-like homeobox transcription factors and partner proteins in establishing the ligule boundary. Mutants will be analyzed in these genes for ligule and branching phenotypes. The third aim tests the hypothesis that the bZIP transcription factor LIGULELESS2 (LG2), bound by KN1, is involved in positioning the blade/sheath boundary. Protein partners will be identified as will down-stream targets to determine the role of LG2 in establishing the blade sheath boundary.