Evolution and Mechanism of a Conserved Regulatory Switch for Mating-Types and Sexes in Volvocine Green Algae

性和重组是真核生物界生命周期和繁殖的组成部分，真核生物包括动物、植物、真菌、海藻和许多单细胞藻类以及其他原生生物。真核生物性别的一个标志涉及遗传系统，如性染色体或交配型基因，以确保交配涉及具有两种不同交配类型或性别的个体。然而，除了动物、真菌和其他一些分类群之外，人们对性别和交配类型是如何决定的，或者雄性和雌性是如何在多细胞物种中从具有交配类型的单细胞祖先进化而来的知之甚少。Volvocine绿色藻类是一组独特的亲属，包括单细胞和小殖民物种交配型，更大的更复杂的物种与性别和性染色体，但他们都有一个共同的遗传系统控制配子分化。根据这一提议，将对volvocine藻类进行研究，以了解在向性别的进化过渡中，控制交配类型的遗传系统是如何被修改的。重要的是，控制volvocine藻类性别和交配类型的遗传机制至少部分地与其他绿色藻类及其陆地植物表亲共享。因此，从这一提议中获得的知识可以影响对植物界中广泛物种的性别决定的理解，并且可以进一步用于新兴藻类作物物种的育种和菌株改良，这些藻类作物物种用于制造高价值的生物产品或生物燃料。然而，几乎在每一个进化出复杂多细胞生物的谱系中，两性异形也是如此，这种转变的起源和机制仍然知之甚少。Volvocine绿色藻类（Chlamydiumreinhardtii，Volvoxcarteri，和亲戚）是一个独特的易处理的模型，用于研究性别分化和两性异形进化的遗传网络。保守的转录因子（TF）MID是volvocine藻类中负配子或雄配子分化的主要指示因子;但负责正配子或雌配子的基础性分化的因子仍然未知。根据这一建议，一个新发现的TF，VSR 1，这是必不可少的两个配子类型和性别的分化volvocine藻类将进行调查。一个新的模型，其中VSR 1同源二聚体和MID-VSR 1异源二聚体之间的竞争相互作用形成一个二元开关的性别或交配类型的决定将进行测试和完善，和MID/VSR 1基因调控网络（GRNs）的扩展和分歧的基础机制过渡到卵受精将进行探索。具体目的是：1）阐明和比较关键的同花受精和卵受精volvocine代表中由MID和VSR 1控制的配子发生的基因表达程序; 2）确定MID-VSR 1物理相互作用的基础以及两个TF在volvocine谱系多样化过程中如何共同进化; 3）在关键的volvocine代表中鉴定VSR 1和MID的DNA结合特异性和直接靶标，以使得能够对性别进行建模。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Sex and recombination are integral to life cycles and reproduction across the kingdom of eukaryotes that includes animals, plants, fungi, seaweeds and many single-celled algae and other protists. A hallmark of eukaryotic sex involves genetic systems such as sex chromosomes or mating type genes to ensure that matings involve individuals with two distinct mating types or sexes. However, outside of animals, fungi, and a few other taxa, little is known about how sexes and mating types are determined or how male and female sexes evolved in multicellular species from single-celled ancestors with mating types. Volvocine green algae are a unique group of relatives that include single celled and small colonial species with mating types, and larger more complex species with sexes and sex chromosomes; but they all share a common genetic system for controlling gamete differentiation. Under this proposal volvocine algae will be investigated to understand how the genetic systems governing mating types were modified in the evolutionary transition to sexes. Importantly, the genetic machinery that controls sexes and mating types in volvocine algae is at least partly shared with other groups of green algae and their land plant cousins. Thus, the knowledge obtained from this proposal can impact the understanding of sex determination in a wide range of species in the plant kingdom and may be further leveraged for breeding and strain improvement in emerging algal crop species that are used to make high value bioproducts or biofuels.Ancestral eukaryotes were single cells with isogamous sexual reproduction. However, in nearly every lineage where complex multicellularity evolved, so did dimorphic sexes—a transition whose origins and mechanisms remain poorly understood. Volvocine green algae (Chlamydomonas reinhardtii, Volvox carteri, and relatives) are a uniquely tractable model for investigating the genetic networks governing sexual differentiation and the evolution of dimorphic sexes. The conserved transcription factor (TF) MID is a dominant specifier of minus or male gamete differentiation in volvocine algae; but the factor(s) responsible for basal sexual differentiation as plus or female have remained unknown. Under this proposal a newly discovered TF, VSR1, that is essential for differentiation of both gamete types and sexes in volvocine algae will be investigated. A new model where competing interactions between VSR1 homodimers and MID-VSR1 heterodimers form a binary switch for sex or mating type determination will be tested and refined, and the mechanisms underlying expansion and divergence of the MID/VSR1 gene regulatory networks (GRNs) during the transition to oogamy will be explored. Specific Aims are designed to 1) Elucidate and compare the gene expression programs for gametogenesis that are governed by MID and VSR1 in key isogamous and oogamous volvocine representatives; 2) Determine the bases for MID-VSR1 physical interactions and how the two TFs co-evolved during diversification of the volvocine lineage; 3) Identify the DNA binding specificity and direct targets of VSR1 and MID in key volvocine representatives to enable modeling of sex-related GRN evolution and testing of hypotheses about GRN expansion in Volvox.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.