Elucidating the genetic basis and molecular mechanism of dioecy in Populus

虽然大多数植物物种是雌雄同体的，但雌花和雄花分离到不同的个体上，称为雌雄异株，已经独立进化了数百次，如果不是数千次的话。尽管如此，潜在的遗传基础仍然是难以捉摸的。在拟议的项目中，我们希望阐明杨树中的dioclonal的遗传和分子基础，以解决有关植物性系统进化的首要问题。尽管白杨属的异源性染色体起源古老，但其潜在的性染色体似乎只是最近才出现分歧。不同白杨种的性别决定区（SDRs）的不同位置和不同的异配子体亲本（XY系统与ZW系统）进一步表明了独立的进化。然而，我们的初步分析表明，观察到的复杂性代表了同一主题的变化。在本研究中，我们希望通过实验验证：（i）白色杨和白杨的SDRs是否缺乏重组抑制区，是否表现出相反的异配子性（XY vs. ZW），（ii）拟南芥反应调节因子17（ARR17）基因的白杨同源物是否通过基于单基因的机制控制整个属的性别决定，以及（iii）引起不同的性别表现的分子机制是否在不同的白杨物种之间是保守的。我们将通过（i）绘制白色白杨SDR，在大的F1群体中确定沿着雄性和雌性的SDR的重组频率沿着，并检查相互的白花山杨x山杨杂交，（ii）产生敲除或补充ARR17表达的早花转基因白杨品系，并对不同白杨物种中的ARR17基因座进行分子表征，以及（iii）对雌雄花蕾进行RNA测序，并将测序结果与其他功能基因组学数据相结合，以确定导致雌雄异株植物性别差异的基因网络，为雌雄异株植物育种提供有价值的信息，并促进我们对植物单性和雌雄异株性形成的遗传、分子和进化过程的理解。

While most plant species are hermaphrodites, the separation of female and male flowers onto different individuals, called dioecy, has evolved independently hundreds if not thousands of times. Still, the underlying genetic basis remains mostly elusive. In the proposed project, we want to elucidate the genetic and molecular basis of dioecy in poplars to address overarching questions concerning the evolution of plant sexual systems. Despite an ancient origin of dioecy in the genus Populus, the underlying sex chromosomes appear to have diverged only recently. Different locations of the sex-determining regions (SDRs) and varying heterogametic parents (XY- vs. ZW-system) in different poplar species further indicate independent evolution. However, our preliminary analyses suggest that the observed complexity represents variations on the same theme. A shared single-gene-based mechanism, with important implications for sex chromosome evolution in general, appears to be underlying dioecy across different Populus species.In the proposed project we want to experimentally test whether (i) the SDRs of white poplar and aspen lack a region of suppressed recombination and show opposite heterogamety (XY vs. ZW), whether (ii) the poplar homolog of the ARABIDOPSIS RESPONSE REGULATOR 17 (ARR17) gene is controlling sex determination across the genus via a single-gene-based mechanism, and whether (iii) the molecular mechanisms causing differential sex manifestation are conserved between different poplar species.We will do this by (i) mapping the white poplar SDR, determining recombination frequencies along the SDRs of males and females in large F1 populations and examining reciprocal P. alba x P. tremula crosses, (ii) generating early-flowering transgenic poplar lines knocking out or complementing ARR17 expression and molecularly characterizing the ARR17 locus in different poplar species, and (iii) performing RNA-sequencing of male and female flower buds and integrating the results with other functional genomics data to identify the gene networks causing differential sex manifestation.The results will provide valuable information for breeding programs involving dioecious crop plants, and advance our understanding of the genetic, molecular and evolutionary processes shaping unisexuality and dioecy in plants.