Thurber Carrie S, Reagon Michael, Olsen Kenneth M, Jia Yulin, Caicedo Ana L
Biology Department, University of Massachusetts, Amherst, Massachusetts 01003 USA.
Department of Biology, The Ohio State University-Lima, Lima, Ohio 45804 USA.
Am J Bot. 2014 Oct;101(10):1737-47. doi: 10.3732/ajb.1400154. Epub 2014 Oct 8.
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Local adaptation in plants often involves changes in flowering time in response to day length and temperature. Many crops have been selected for uniformity in flowering time. In contrast, variable flowering may be important for increased competitiveness in weed species invading the agricultural environment. Given the shared species designation of cultivated rice (Oryza sativa) and its the invasive conspecific weed, weedy rice, we assessed the extent to which flowering time differed between these groups. We further assessed whether genes affecting flowering time variation in rice could play a role in the evolution of weedy rice in the United States.•
We quantified flowering time under day-neutral conditions in weedy, cultivated, and wild Oryza groups. We also sequenced two candidate gene regions: Hd1, a locus involved in promotion of flowering under short days, and the promoter of Hd3a, a locus encoding the mobile signal that induces flowering.•
We found that flowering time has diverged between two distinct weedy rice groups, such that straw-hull weeds tend to flower earlier and black-hull awned weeds tend to flower later than cultivated rice. These differences are consistent with weed Hd1 alleles. At both loci, weeds share haplotypes with their cultivated progenitors, despite significantly different flowering times.•
Our phenotypic data indicate the existence of multiple flowering strategies in weedy rice. Flowering differences between weeds and ancestors suggest this trait has evolved rapidly. From a weed management standpoint, there is the potential for overlap in flowering of black-hull awned weeds and crops in the United States, permitting hybridization and the potential escape of genes from crops.
植物的局部适应性通常涉及开花时间随日照长度和温度的变化。许多作物已被选育为开花时间一致。相比之下，可变开花可能对入侵农业环境的杂草物种提高竞争力很重要。鉴于栽培稻（Oryza sativa）及其入侵性同种杂草杂草稻共享物种名称，我们评估了这两组之间开花时间的差异程度。我们还进一步评估了影响水稻开花时间变异的基因是否在美国杂草稻的进化中发挥作用。
我们在日中性条件下对杂草稻、栽培稻和野生稻组的开花时间进行了量化。我们还对两个候选基因区域进行了测序：Hd1，一个在短日条件下促进开花的基因座，以及Hd3a的启动子，Hd3a是一个编码诱导开花的移动信号的基因座。
我们发现，在两个不同的杂草稻组之间开花时间已经分化，使得稻草壳杂草往往比栽培稻开花更早，而黑壳有芒杂草往往比栽培稻开花更晚。这些差异与杂草的Hd1等位基因一致。在这两个基因座上，杂草与其栽培祖先共享单倍型，尽管开花时间有显著差异。
我们的表型数据表明杂草稻存在多种开花策略。杂草与其祖先之间的开花差异表明这一性状已经迅速进化。从杂草管理的角度来看，美国黑壳有芒杂草和作物的开花可能存在重叠，从而允许杂交以及作物基因的潜在逃逸。
