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

在作物驯化过程中，植物结构的改变一直是至关重要的。通过几代人的育种来提高产量，农作物被选择了各种分枝模式，这些模式改变了分枝的数量、长度或角度。在玉米中，叶片角度一直是一个重要的分枝性状，可能有助于提高玉米产量。叶片的角度由叶舌区域决定，叶舌区域形成于叶片和叶鞘的交界处。叶片向后倾斜，以吸收来自太阳的能量，而鞘紧贴在茎上。叶片和叶鞘之间的这种角度是一种可遗传的特征，可以通过选择进行修改：减少角度使植株更直立，以适应更紧凑的田地，而增加角度则优化叶片的表面积，以获得更多能量。因此，了解建立叶片角度的基本分子机制将为操纵玉米的结构提供新的工具。该项目旨在阐明决定舌状区形成时间和方式的复杂因素网络。这个项目将首先确定和表征在发育的最早阶段定义舌叶边界的基因的表达。然后将使用分子、遗传和基因组方法来研究舌状区是如何形成的。结果将与不同的受众分享，包括饲养者、科学界和学生。为此，将制作YouTube视频，向普通观众描述玉米发育的科学，并将为学生课堂制作额外的教育材料。所有资源将通过实验室网站和玉米社区网站(http://www.maizegdb.org).)公开提供这个项目研究了在未分化的叶原基中，舌状区是如何被确定为器官边界的。以前的工作使用解剖上不同的叶舌作为转录组分析的位置：前叶舌、前叶片和前健康细胞被清楚地识别为激光捕获随后的RNA测序。由于捕获的特异性，确定了一组在舌状区唯一和差异表达的候选基因。其他器官边界的共同表达模式表明，叶舌重复了发生在茎顶端分生组织和雄穗分生组织边界的侧向器官起始程序。因此，不同的器官边界被假设为共享基因，并使用共同的机制来定义和限制发育途径。为了验证这一假说，将建立舌叶发育的早期阶段的基因网络，并进一步研究舌叶起始的机制。第一个具体目标是通过从最年轻的可接近的叶原基中捕获细胞来识别叶舌形成的最早决定因素。候选基因将根据它们在其他叶舌特定突变体中的表达情况进行优先排序。第二个目的是研究三条有希望的候选基因通路，它们支持KNOTTED1(KN1)样同源盒转录因子和伙伴蛋白在建立舌叶边界中的作用。突变体将在这些基因中进行叶舌和分枝表型的分析。第三个目的是测试bZIP转录因子LIGULESS2(LG2)与KN1结合，参与定位刀片/鞘边界的假设。蛋白质伙伴将被确定为下游目标，以确定LG2在建立叶片鞘边界中的作用。

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.