Genetic analysis of environmental control of inflorescence development in perennial Arabis alpina

季节变化和日长决定了植物开花的适当时间，以确保随后种子的最佳生产。在十字花科植物如阿拉比斯高山油菜和甘蓝型油菜中，花的形成分两步进行，一年内形成花蕾，第二年春天长出花芽。然而，在多年生植物中，花蕾停滞和花序生长的季节性调节背后的遗传机制还没有得到研究。在这个项目中，将使用两种不同的方法来分析这些机制。首先，将对挪威的高山阿拉伯种群进行正向遗传QTL分析，该种群显示了开花时间的自然变异，并包含早花和晚花的个体。在早花和晚花植物中，花芽在没有春化的情况下形成的时间大致相同；然而，晚花植物的花芽停止并产生成熟的花序的速度要慢得多。这两种类型的春化克服了晚花亲本的花芽停滞表型，并且在春化后不久，两种类型的花几乎同时开花。这表明这两个材料在阻止晚型花芽开放的检查点上存在遗传差异，这可以通过春化来克服。寄主群体已经确定了一个影响花芽停滞表型的QTL。QTL已经定位在8号染色体的一个700 kb的基因组片段上，在近等基因系中，该基因座是分离的，该区域已经从PacBio Reads组装而来。环境决定的芽阻表型的致病基因将通过进一步的重组作图来确定，其功能将通过表达分析和转基因来分析。其次，拟南芥FT基因促进长日照开花，并被认为调节拟南芥的花序发育和花芽开放。然而，编码成花原的FT基因在多年生十字花科植物(如高山芥菜)成花诱导中的作用尚未得到分析，主要是因为AaFT零等位基因不可用。因此，利用CRISPR-Cas9反向遗传方法获得4个AaFT基因的敲除突变体，用来研究这些基因在不同光周期和春化后对花诱导、花发育和花序发育的单独和联合作用。这两种方法不仅将有助于确定晚花高山阿拉伯花芽停滞表型的偶然基因，并有助于建立目前的模型，即秋季春化过程中形成的花芽如何在春季产生开放的花和花序，而且还将允许对相关一年生和多年生物种中成花基因的功能进行比较分析。

Seasonal changes and daylength determine the appropriate timing of flowering in plants, to ensure the subsequent optimal production of seeds. In crucifers such as Arabis alpina and Brassica napus, the formation of flowers takes place in a two-step procedure, whereby buds are formed in one year and their outgrowth occurs in the following spring. However, the genetic mechanisms that underlie the seasonal regulation of bud arrest and inflorescence growth have not been examined in perennial plants. In this project, two different approaches will be used to analyse these mechanisms. First, a forward-genetic, QTL analysis will be applied to a Norwegian population of Arabis alpina that shows natural variation for flowering time and contains early- and late-flowering individuals. In early-, and late-flowering plants, floral buds are formed without vernalization at an approximately similar time; however, the floral buds of late-flowering plants arrest and generate mature inflorescences much more slowly. Vernalization of both genotypes overcomes the floral bud-arrest phenotype of the late-flowering parent, and both types flower at approximately the same time soon after vernalization. This suggests that these two accessions differ genetically at a checkpoint that arrests floral bud opening of the late type and that this can be overcome by vernalization. The host group has identified a QTL that contributes to the floral bud-arrest phenotype. The QTL has been localised to a 700-kb genomic segment of chromosome 8 in near-isogenic lines in which the locus segregates and the region has been assembled from PacBio reads. The causal gene responsible for the environmentally determined bud-arrest phenotype will be identified by further rounds of recombination mapping and its function will be analysed by expression analysis and transgenesis. Second, the Arabidopsis thaliana FT gene promotes flowering in long days and is proposed to regulate inflorescence development and flower-bud opening in Arabidopsis lyrata. However, the contribution of florigen-encoding FT genes to floral induction of perennial Brassicaceae such as Arabis alpina has not been analysed, mainly because AaFT null alleles are not available. Therefore, a reverse-genetic approach using CRISPR-Cas9 will be employed to generate knockout mutants of four AaFT genes with which to study the individual and combined contributions of the genes to floral induction, floral development and inflorescence development in different photoperiods and following vernalization. The two proposed approaches will not only identify the casual gene responsible for the bud-arrest phenotype in late-flowering Arabis alpina and contribute to current models for how floral buds formed during vernalization in autumn only produce open flowers and inflorescences in spring, but will allow comparative analysis of the function of florigen genes in related annual and perennial species.