Understanding the mechanism of sexual development in Chlamydomonas reinhardtii

了解莱茵衣藻的性发育机制

• 批准号: RGPIN-2019-06385
• 负责人: Lee, JaeHyeok
• 金额: $ 3.42万
• 依托单位: University of British Columbia
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=716014
• 关键词: Understanding; mechanism; sexual; development; Chlamydomonas

Sexual development is the primary reproductive strategy of plants, governing the processes directly affecting the yields of grains and beans. During plant sexual development, pollens deliver male gametes to egg cells, and fertilized female gametes develop into embryo and endosperm, which maturate into a dormant seed. Understanding the mechanisms of post-fertilization development is a key objective of plant biologists and agricultural sectors. Pioneering studies in the unicellular green alga, Chlamydomonas reinhardtii, have identified critical factors for gametic cell fusion and subsequent zygote development. Chlamydomonas zygote development is initiated by two sexual gametes of equal size, whose fusion combines two homeobox transcription factors, Gsm1 and Gsp1. Our recent study shows that the Gsm1/Gsp1 heterodimer initiates transcription of ~94% of the early zygote-specific genes and trigger post-fertilization development, including zygotic wall assembly and parent-specific elimination of organelle DNAs, consequently leading to produce dormant zygospores resembling the plant seeds. Plant homologs of Gsm1/Gsp1 are required and sufficient for the haploid-to-diploid transition in the moss, Physcomitrella patens, indicating functional homology of the molecules involved in sexual development between Chlamydomonas and plants. Thus, Chlamydomonas represents an excellent model system for genetic dissection of the conserved regulatory mechanisms of sexual development. To investigate the molecular mechanisms of sexual development in Chlamydomonas, our research program employed three different approaches. First, we engineered a self-mating strain that readily produces homozygous diploids from a clonal cell population. Using the self-mating strain, we identified critical factors for developmental transition and zygote differentiation. Second, we investigated elusive factors residing on the sex-determining MTL+ (Mating Type Locus plus), controlling the uniparental inheritance (UPI) of chloroplast DNA. We identified an MTL+ specific gene required for protecting the plus cpDNA from degradation. Third, we used a swimming-based reporter system probing the transcription activated under Nitrogen (N) starvation and identified crucial factors sensing and responding to the cellular N status. The results from these approaches provide genetic evidence for the gene regulatory mechanisms governing two cellular differentiation programs for gametes and zygotes. In this proposal, I propose a research program with five short-term projects investigating: 1. How PAF1 complex ensures the zygote differentiation. 2. The roles of the RNAi system in the haploid-to-diploid transition. 3. The molecular mechanism governing the uniparental elimination of chloroplast DNA. 4. The signal transduction mechanisms for the N starvation-induced transcription.

性发育是植物的主要生殖策略，控制着直接影响谷物和豆类产量的过程。在植物性发育过程中，花粉将雄配子传递给卵细胞，受精的雌配子发育成胚和胚乳，胚和胚乳成熟成休眠的种子。了解受精后发育的机制是植物生物学家和农业部门的一个重要目标。 在单细胞绿色衣藻，莱茵衣藻的开拓性研究，已经确定了配子细胞融合和随后的合子发育的关键因素。衣原体受精卵的发育是由两个大小相等的有性配子启动的，它们的融合结合了两个同源框转录因子Gsm 1和Gsp 1。我们最近的研究表明，Gsm 1/Gsp 1异二聚体启动约94%的早期合子特异性基因的转录，并触发受精后发育，包括合子壁组装和亲本特异性细胞器DNA消除，从而导致产生类似于植物种子的休眠接合孢子。植物同源物Gsm 1/Gsp 1是所需的和足够的单倍体到二倍体的过渡苔藓，小立碗藓，表明功能同源性的分子参与性发育之间的衣原体和植物。因此，衣原体代表了一个很好的模型系统的遗传解剖保守的性发育调控机制。 为了研究衣原体性发育的分子机制，我们的研究计划采用了三种不同的方法。首先，我们设计了一种自交配菌株，它很容易从克隆细胞群中产生纯合二倍体。使用自交配株，我们确定了发育转变和受精卵分化的关键因素。其次，我们研究了性别决定基因MTL+（交配型基因座加）上的难以捉摸的因素，控制叶绿体DNA的单亲遗传（UPI）。我们鉴定了一个MTL+特异性基因，该基因是保护plus cpDNA不被降解所必需的。第三，我们使用了一个基于游泳的报告系统探测氮（N）饥饿下激活的转录，并确定了传感和响应细胞N状态的关键因子。 这些方法的结果为配子和合子两种细胞分化程序的基因调控机制提供了遗传学证据。 在这份提案中，我提出了一个研究计划，包括五个短期项目，调查： 1. PAF 1复合体如何保证合子分化。 2. RNAi系统在单倍体到二倍体转变中的作用。 3.叶绿体DNA单亲消除的分子机制。 4. N饥饿诱导转录的信号转导机制。