Evolution of gametophytic communication systems by analyzing RALF and ROS signaling

陆生植物生殖器官和配子的进化伴随着配子/配子体通讯系统的许多变化和适应。虽然单细胞藻类（如衣原体）的相反交配类型的配子在水环境中进行交流，但水藻和蕨类植物产生移动的精细胞，这些精细胞在潮湿的环境中被卵细胞吸引。裸子植物和被子植物对干燥环境的适应伴随着精细胞活动性的丧失和花粉粒（雄配子体）的发明，花粉粒通过风或动物长距离保护和携带精细胞到雌花器官。此外，花粉粒形成一个深入母体花器官的管，以释放其精子细胞货物，用于胚囊（雌性配子体）内的受精。在陆地植物进化过程中，单细胞藻类配子体间的相互作用变得越来越复杂，而被子植物配子体间的相互作用也越来越复杂。近15年来，以被子植物模式植物拟南芥和玉米为研究对象，对配子体通讯的分子和机制的研究取得了很大进展。特别是分泌的多态性富含半胱氨酸肽（CRPs）似乎在花粉管萌发、生长、引导和接受过程中发挥着核心作用。其中，花粉管特异性RALF（快速碱化因子）肽最近被证明可以调节拟南芥中的花粉管完整性和精子释放。虽然单细胞藻类不包含RALF基因，但在苔藓中存在由几个基因组成的古老RALF分支，并且RALF基因的数量在进化过程中被强烈扩增到37个基因，例如，在拟南芥中。到目前为止，据我们所知，只有RALF基因相关的古老的分支已被功能特点和激活活性氧产生拟南芥。因此，本项目的目的是通过研究两个基因家族及其相互作用，有助于理解配子体串扰的进化。(i)我们将研究RALF基因家族成员的进化，多样化和规范，包括古老的RALF在苔藓和一个新的分支在玉米中缺乏典型的RALF肽签名的功能研究。研究还将包括利用来自不同陆地植物的RALF对拟南芥和玉米花粉突变体进行互补分析。将使用已知受体进行相互作用研究。(ii)我们将进一步调查和比较保守的RALF触发ROS生产的苔藓和被子植物的合作，（iii）研究主要的ROS生产RBOH基因在玉米乳突毛细胞花粉粘附后。

The evolution of reproductive organs and gametes of land plants was accompanied by numerous changes and adaptations of gametic/gametophytic communication systems. While gametes of opposite mating types of single celled algae like Chlamydomonas communicate in a watery environment, bryophytes and ferns generate mobile sperm cells, which are attracted by egg cells in a moist environment. Adaptations to dry environments in gymnosperms and angiosperms were accompanied by loss of sperm cell mobility and the invention of pollen grains (male gametophyte), that protect and carry sperm cells by wind or animals over long distances to female flower organs. Moreover, pollen grains form a tube that growths deeply into the maternal flower organs to release its sperm cell cargo for fertilization inside the embryo sac (female gametophyte). The complexity of gametic cross-talk in single celled algae towards gametophytic cross-talk in angiosperms has enormously increased during land plant evolution. By using the angiosperm model plants Arabidopsis and maize, a lot of progress has been made in the past 15 years to elucidate molecules and mechanisms involved in gametophyte communication. Especially secreted polymorphic cysteine-rich peptides (CRPs) appear to play a central role during pollen tube germination, growth, guidance and reception. Among these, pollen tube-specific RALF (Rapid ALkalinization Factor) peptides were recently shown to regulate pollen tube integrity and sperm release in Arabidopsis. While single celled algae do not contain RALF genes, an ancient RALF clade consisting of a few genes exists in mosses, and the number of RALF genes was strongly amplified during evolution to 37 genes, for example, in Arabidopsis. Until now, to our knowledge, only RALF genes related to the ancient clade have been functionally characterized and activate ROS production in Arabidopsis. The aim of this project therefore is to contribute to the understanding of the evolution of gametophytic cross-talk by studying two gene families and their interaction(s). (i) We will study the evolution, diversification and specification of members of the RALF gene family including functional studies of ancient RALFs in a moss and a novel clade in maize lacking the typical RALF peptide signature. Studies will also include complementation analyses of Arabidopsis and maize pollen mutants using RALFs from different land plant. Interaction studies will be performed with known receptors. (ii) We will further investigate and compare the conservation of RALF-triggered ROS production in mosses and angiosperms in collaboration, and (iii) study major ROS-producing RBOH genes in papilla hair cell of maize after pollen adhesion.