Max Planck Institute for Plant Breeding Research, Cologne, Germany.
PLoS Genet. 2012;8(12):e1003130. doi: 10.1371/journal.pgen.1003130. Epub 2012 Dec 20.
Higher plants exhibit a variety of different life histories. Annual plants live for less than a year and after flowering produce seeds and senesce. By contrast perennials live for many years, dividing their life cycle into episodes of vegetative growth and flowering. Environmental cues control key check points in both life histories. Genes controlling responses to these cues exhibit natural genetic variation that has been studied most in short-lived annuals. We characterize natural genetic variation conferring differences in the perennial life cycle of Arabis alpina. Previously the accession Pajares was shown to flower after prolonged exposure to cold (vernalization) and only for a limited period before returning to vegetative growth. We describe five accessions of A. alpina that do not require vernalization to flower and flower continuously. Genetic complementation showed that these accessions carry mutant alleles at PERPETUAL FLOWERING 1 (PEP1), which encodes a MADS box transcription factor orthologous to FLOWERING LOCUS C in the annual Arabidopsis thaliana. Each accession carries a different mutation at PEP1, suggesting that such variation has arisen independently many times. Characterization of these alleles demonstrated that in most accessions, including Pajares, the PEP1 locus contains a tandem arrangement of a full length and a partial PEP1 copy, which give rise to two full-length transcripts that are differentially expressed. This complexity contrasts with the single gene present in A. thaliana and might contribute to the more complex expression pattern of PEP1 that is associated with the perennial life-cycle. Our work demonstrates that natural accessions of A. alpina exhibit distinct life histories conferred by differences in PEP1 activity, and that continuous flowering forms have arisen multiple times by inactivation of the floral repressor PEP1. Similar phenotypic variation is found in other herbaceous perennial species, and our results provide a paradigm for how characteristic perennial phenotypes might arise.
高等植物表现出多种不同的生活史。一年生植物的寿命不到一年，开花后产生种子并衰老。相比之下，多年生植物可以存活多年，将其生命周期分为营养生长和开花两个阶段。环境线索控制着这两种生活史的关键检查点。控制对这些线索反应的基因表现出自然遗传变异，这种变异在短命的一年生植物中得到了最广泛的研究。我们描述了赋予拟南芥多年生生活史差异的自然遗传变异。先前的 Pajares 品系被证明在长时间暴露于寒冷（春化）后开花，并且在返回营养生长之前只能开花有限的时间。我们描述了五个不需要春化即可开花且持续开花的拟南芥品系。遗传互补表明，这些品系在 PERPETUAL FLOWERING 1 (PEP1) 基因中携带突变等位基因，该基因编码与一年生拟南芥中的开花位点 C 同源的 MADS 框转录因子。每个品系在 PEP1 上携带不同的突变，表明这种变异已经独立发生了多次。这些等位基因的特征表明，在大多数品系中，包括 Pajares，PEP1 基因座包含一个全长和一个部分 PEP1 拷贝的串联排列，这导致两个全长转录本的差异表达。这种复杂性与拟南芥中存在的单个基因形成对比，可能有助于与多年生生活周期相关的 PEP1 更复杂的表达模式。我们的工作表明，拟南芥的自然品系表现出不同的生活史，这是由 PEP1 活性的差异所决定的，并且连续开花形式已经通过 PEP1 花抑制因子的失活多次出现。在其他草本多年生植物物种中也发现了类似的表型变异，我们的结果为典型的多年生表型如何出现提供了范例。
