Data_Sheet_6.XLSX

Leaf thickness is a quantitative trait that is associated with the ability of plants to occupy dry, high irradiance environments. Despite its importance, leaf thickness has been difficult to measure reproducibly, which has impeded progress in understanding its genetic basis, and the associated anatomical mechanisms that pattern it. Here, we used a custom-built dual confocal profilometer device to measure leaf thickness in the Arabidopsis Ler × Cvi recombinant inbred line population and found statistical support for four quantitative trait loci (QTL) associated with this trait. We used publically available data for a suite of traits relating to flowering time and growth responses to light quality and show that three of the four leaf thickness QTL coincide with QTL for at least one of these traits. Using time course photography, we quantified the relative growth rate and the pace of rosette leaf initiation in the Ler and Cvi ecotypes. We found that Cvi rosettes grow slower than Ler, both in terms of the rate of leaf initiation and the overall rate of biomass accumulation. Collectively, these data suggest that leaf thickness is tightly linked with physiological status and may present a tradeoff between the ability to withstand stress and rapid vegetative growth. To understand the anatomical basis of leaf thickness, we compared cross-sections of Cvi and Ler leaves and show that Cvi palisade mesophyll cells elongate anisotropically contributing to leaf thickness. Flow cytometry of whole leaves show that endopolyploidy accompanies thicker leaves in Cvi. Overall, our data suggest that mechanistically, an altered schedule of cellular events affecting endopolyploidy and increasing palisade mesophyll cell length contribute to increase of leaf thickness in Cvi. Ultimately, knowledge of the genetic basis and developmental trajectory leaf thickness will inform the mechanisms by which natural selection acts to produce variation in this adaptive trait.

叶片厚度是一类与植物适应干旱、高辐照环境能力相关的数量性状。尽管该性状具有重要研究价值，但叶片厚度的可重复测量始终存在难点，这极大阻碍了学界对其遗传基础及调控其形成的相关解剖学机制的研究进展。本研究使用定制化双共聚焦轮廓仪（dual confocal profilometer），对拟南芥Ler × Cvi重组自交系群体的叶片厚度进行测量，并通过统计学分析验证了4个与该性状相关的数量性状位点（quantitative trait loci, QTL）。我们利用公开的一系列与开花时间、光质生长响应相关的性状数据，发现4个叶片厚度相关QTL中的3个，与至少1个上述性状的QTL存在重叠。通过延时摄影技术，我们对Ler和Cvi生态型的相对生长速率及莲座叶起始速率进行了定量分析。结果显示，无论是叶片起始速率还是生物量整体积累速率，Cvi莲座株系的生长速度均慢于Ler。综合上述结果可知，叶片厚度与植株生理状态紧密相关，可能在胁迫耐受能力与快速营养生长之间存在权衡关系。为解析叶片厚度的解剖学基础，我们对比了Cvi与Ler的叶片横切面，发现Cvi的栅栏组织叶肉细胞通过各向异性伸长，进而增加叶片厚度。全叶片流式细胞术分析结果表明，Cvi叶片较厚的表型伴随内多倍化水平的升高。综上，本研究数据表明，从机制层面来看，影响内多倍化进程并延长栅栏组织叶肉细胞长度的细胞事件时序改变，是Cvi叶片厚度增加的原因。最终，解析叶片厚度的遗传基础与发育轨迹，将有助于理解自然选择如何作用于该适应性性状并产生其表型变异的机制。