Department of Forest and Conservation Sciences, Faculty of Forestry, Forest Sciences Centre, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
Department of Dendrology and Forest Tree Breeding, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, 165 21, Czech Republic.
New Phytol. 2018 Oct;220(1):300-316. doi: 10.1111/nph.15273. Epub 2018 Jul 2.
Spring bud-break phenology is a critical adaptive feature common to temperate perennial woody plants. Understanding the molecular underpinnings of variation in bud-break is important for elucidating adaptive evolution and predicting outcomes relating to climate change. Field and controlled growth chamber tests were used to assess population-wide patterns in bud-break from wild-sourced black cottonwood (Populus trichocarpa) genotypes. We conducted a genome-wide association study (GWAS) with single nucleotide polymorphisms (SNPs) derived from whole genome sequencing to test for loci underlying variation in bud-break. Bud-break had a quadratic relationship with latitude, where southern- and northern-most provenances generally broke bud earlier than those from central parts of the species' range. Reduced winter chilling increased population-wide variation in bud-break, whereas greater chilling decreased variation. GWAS uncovered 16 loci associated with bud-break. Phenotypic changes connected with allelic variation were replicated in an independent set of P. trichocarpa trees. Despite phenotypic similarities, genetic profiles between southern- and northern-most genotypes were dissimilar based on our GWAS-identified SNPs. We propose that the GWAS-identified loci underpin the geographical pattern in P. trichocarpa and that variation in bud-break reflects different selection for winter chilling and heat sum accumulation, both of which can be affected by climate warming.
芽休眠期是温带多年生木本植物的一个关键适应性特征。了解芽休眠期变异的分子基础对于阐明适应性进化和预测与气候变化有关的结果非常重要。本研究利用野外和受控生长室试验评估了源自野生黑杨（Populus trichocarpa）基因型的芽休眠期的种群范围模式。我们利用全基因组测序获得的单核苷酸多态性（SNP）进行了全基因组关联研究（GWAS），以测试芽休眠期变异的潜在基因座。芽休眠期与纬度呈二次关系，最南端和最北端的种源通常比物种分布中心的种源更早地打破休眠。冬季休眠减少增加了芽休眠期的种群范围变异，而休眠增加则减少了变异。GWAS 发现了 16 个与芽休眠期相关的位点。与等位基因变异相关的表型变化在一组独立的黑杨树上得到了复制。尽管表型相似，但根据我们的 GWAS 鉴定的 SNP，最南端和最北端基因型之间的遗传特征不同。我们提出，GWAS 鉴定的基因座是黑杨地理模式的基础，而芽休眠期的变异反映了冬季休眠和热积累的不同选择，这两者都可能受到气候变暖的影响。
