Elucidating the genetic basis and molecular mechanism of dioecy in Populus

虽然大多数植物都是雌雄同体，但雌雄花和雄花在不同个体上的分离，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难以捉摸。在本项目中，我们希望阐明杨树雌雄异株的遗传和分子基础，以解决有关植物性系统进化的总体问题。尽管在杨树属中雌雄异株有一个古老的起源，但潜在的性染色体似乎只是最近才分化。不同树种性别决定区（SDRs）的不同位置和异交亲本（XY- vs. zw系统）的不同进一步表明了独立进化。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。一个共同的基于单基因的机制，具有重要意义的性染色体进化，似乎是潜在的雌雄异株在不同的杨树物种。在本项目中，我们希望通过实验验证(i)白杨和白杨的sdr是否缺乏一个抑制重组的区域，并表现出相反的异质性（XY vs. ZW）， （ii）拟南芥应答调节因子17 （ARR17）基因的同源性是否通过单基因机制控制整个属的性别决定，以及（iii）导致性别表现差异的分子机制是否在不同的杨树物种之间保守。我们将通过(i)绘制白杨SDR图谱，确定大型F1群体中雄性和雌性SDR的重组频率，并检查白杨与白杨的互易杂交，（ii）产生敲除或互补ARR17表达的早花转基因杨树系，并在不同杨树物种中对ARR17位点进行分子表征。（iii）对雄性和雌性花蕾进行rna测序，并将结果与其他功能基因组学数据相结合，确定导致性别差异表现的基因网络。该研究结果将为作物的雌雄异株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.