The regulation of meristem development in Ceratopteris gametophytes and sporophytes

植物顶端分生组织含有干细胞，存在于植物生长的顶端，是植物生长和长出叶子、花、果实和种子所必需的。在三亿多年的时间里，嫩枝分生组织已经从包括蕨类植物在内的非种子植物中的简单结构进化为开花植物中的复杂结构。使用Ceratopteris(被称为C-蕨类)作为模式，这项工作询问了陆地植物分生组织的进化。在其生活史中，C-蕨类植物在单倍体配子体和二倍体孢子体阶段之间交替，两者都有非常明显的分生组织。这项研究阐述了分生组织的发育在这两代中是如何被调节的。这项研究利用Ceratopteris作为一种有效和受欢迎的教育工具来吸引K-12科学教师、高中生和本科生。通过暑期研讨会，来自印第安纳州和伊利诺伊州的高中科学教师，包括那些生物教育资源有限的教师，获得动手培训，为他们的生物课开发互动实验室练习。普渡大学通过既定的暑期项目招募的来自代表性不足群体的高中生直接参与了这项研究。该项目的各个方面也被整合到研究人员教授的本科课程中，包括植物解剖学、发育和系统学。例如，植物解剖学的实验室练习包括对野生型和转基因植物的蕨类配子体进行显微观察和量化，为本科生提供独特的机会，在获得实践研究经验的同时受益于研究项目。种子植物的顶端分生组织(SAM)通常由具有不同细胞类型的多个细胞层组成，例如，大多数被子植物的膜-体组织。相比之下，包括蕨类植物在内的非种子维管束植物的自交联体是简单的，由一个大的顶端初始细胞及其衍生物组成。此外，非种子维管束植物在其独立的、单倍体和自由生活的配子体中形成分生组织；而种子植物配子体没有分生组织，依赖于周围的二倍体孢子体组织。这些差异提出了两个重要但尚未解决的问题：配子体和孢子体分生组织是否受蕨类植物中共同的途径调控，以及种子植物中复杂的SAM和非种子维管植物中的简单SAM是否受类似的机制控制？以蕨类植物Ceratopteris richardii为模型系统，该研究采用了多种方法来解决这些问题，包括转录组和系统发育分析、基因编辑和基因沉默、针对基因、蛋白质和不同细胞类型的荧光记者的延时实时成像，以及计算图像量化。这项研究对于揭示分生组织调节剂在非种子维管束植物中的祖先功能，以及揭示模式蕨类植物单倍体配子体分生组织和二倍体孢子体分生组织发生和维持的分子机制具有很大的潜力。鉴于干细胞的重要性和陆地植物分生组织的保守功能，这项工作为理解种子植物中观察到的复杂分生组织是如何从蕨类植物典型的简单分生组织进化而来的奠定了基础。这一奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Plant shoot apical meristems, which contain stem cells and are found at the growing tips of plants, are essential for plants to grow tall and make leaves, flowers, fruits and seeds. Over three hundred million years, shoot meristems have evolved from a simple structure in non-seed plants, including ferns, to a complex structure in flowering plants. Using Ceratopteris (known as C-fern) as a model, the work interrogates the evolution of the meristem in land plants. In its life cycle, C-fern alternates between a haploid gametophyte and a diploid sporophyte stage, both having very distinct meristems. This research addresses how meristem development is regulated during these two generations. The research takes advantage of Ceratopteris as an effective and popular educational tool to engage K-12 science teachers, high school students, and undergraduates. Through summer workshops, high school science teachers from Indiana and Illinois, including those with limited resources for biology education, gain hands-on training to develop interactive lab exercises for their biology classes. High school students from underrepresented groups, recruited through established summer programs at Purdue, directly participate in the research. Aspects of the project also are integrated into undergraduate courses that the investigators teach, including plant anatomy, development and systematics. Lab exercises in plant anatomy, for example, include microscopic observations and quantification of fern gametophytes from wild type and transgenic plants, providing unique opportunities for undergraduates to get hands-on research experiences while benefiting the research project.Shoot apical meristems (SAMs) of seed plants are typically composed of multiple cell layers with distinct cell types, for example, the tunica-corpus organization in most angiosperms. In contrast, SAMs of non-seed vascular plants, including ferns, are simple, composed of a single large apical initial cell and its derivatives. Furthermore, non-seed vascular plants develop meristems in their independent, haploid and free-living gametophytes; whereas seed plant gametophytes do not have a meristem and are dependent on surrounding diploid sporophytic tissues. These differences raise two important but unresolved questions: are gametophyte and sporophyte meristems regulated by common pathways in ferns, and are the complex SAMs in seed plants and the simple SAMs in non-seed vascular plants controlled by similar mechanisms? Using the fern Ceratopteris richardii as a model system, the research tackles these questions employing multiple approaches, including transcriptome and phylogenetic analyses, gene-editing and gene silencing, time-lapse live imaging of fluorescence reporters for genes, proteins and distinct cell types, and computational image quantification. The research has great potential to reveal the ancestral function of meristem regulators in non-seed vascular plants, and uncover the molecular mechanisms underlying the initiation and maintenance of haploid gametophyte meristems and diploid sporophyte meristems of a model fern species. Given the importance of stem cells and the conserved function of the meristems in land plants, this work lays the groundwork for understanding how complex meristems observed in seed plants evolved from the simple meristems typical of ferns.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.