Swanson Robert J, Hammond Adam T, Carlson Ann L, Gong Hui, Donovan Thad K
Department of Biology, Valparaiso University, Valparaiso, Indiana 46383 USA
Biophysical Sciences, The University of Chicago, Chicago, Illinois 60637 USA.
Am J Bot. 2016 Mar;103(3):498-513. doi: 10.3732/ajb.1500172. Epub 2016 Feb 29.
The lack of ability to measure pollen performance traits in mixed pollinations has been a major hurdle in understanding the mechanisms of differential success of compatible pollen donors. In previous work, we demonstrated that nonrandom mating between two accessions of Arabidopsis thaliana, Columbia (Col) and Landsberg (Ler), is mediated by the male genotype. Despite these genetic insights, it was unclear at what stage of reproduction these genes were acting. Here, we used an experimental strategy that allowed us to differentiate different pollen populations in mixed pollinations to ask: (1) What pollen performance traits differed between Col and Ler accessions that direct nonrandom mating? (2) Is there evidence of interference competition?
We used genetically marked pollen that can be visualized colorimetrically to quantify pollen performance of single populations of pollen in mixed pollinations. We used this and other assays to measure pollen viability, germination, tube growth, patterns of fertilization, and seed abortion. Finally, we assessed interference competition.
In mixed pollinations on Col pistils, Col pollen sired significantly more seeds than Ler pollen. Col pollen displayed higher pollen viability, faster and greater pollen germination, and faster pollen tube growth. We saw no evidence of nonrandom seed abortion. Finally, we found interference competition occurs in mixed pollinations.
The lack of differences in postzygotic processes coupled with direct observation of pollen performance traits indicates that nonrandom mating in Arabidopsis thaliana is prezygotic, due mostly to differential pollen germination and pollen tube growth rates. Finally, this study unambiguously demonstrates the existence of interference competition.
在混合授粉中缺乏测量花粉性能特征的能力一直是理解兼容花粉供体差异成功机制的主要障碍。在先前的研究中，我们证明了拟南芥两个生态型哥伦比亚（Col）和兰茨贝格（Ler）之间的非随机交配是由雄性基因型介导的。尽管有这些遗传学见解，但尚不清楚这些基因在生殖的哪个阶段起作用。在这里，我们采用了一种实验策略，使我们能够在混合授粉中区分不同的花粉群体，以探讨：（1）在指导非随机交配的Col和Ler生态型之间，哪些花粉性能特征存在差异？（2）是否有干扰竞争的证据？
我们使用了可通过比色法可视化的基因标记花粉，以量化混合授粉中单个花粉群体的花粉性能。我们使用此方法和其他测定方法来测量花粉活力、萌发、花粉管生长、受精模式和种子败育。最后，我们评估了干扰竞争。
在对Col雌蕊进行的混合授粉中，Col花粉产生的种子明显多于Ler花粉。Col花粉表现出更高的花粉活力、更快且更强的花粉萌发以及更快的花粉管生长。我们没有发现非随机种子败育的证据。最后，我们发现在混合授粉中存在干扰竞争。
合子后过程缺乏差异，再加上对花粉性能特征的直接观察，表明拟南芥中的非随机交配是合子前的，主要是由于花粉萌发和花粉管生长速率的差异。最后，这项研究明确证明了干扰竞争的存在。
