Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, and College of Life Sciences, Beijing Normal University, Beijing, China.
School of Life Sciences, Peking University, Beijing, China.
Ann Bot. 2018 Feb 12;121(2):255-266. doi: 10.1093/aob/mcx152.
To understand the link between species diversity and phenotype developmental evolution is an important issue in evolutionary biology. Yarrows in the genus Achillea (Asteraceae) show a great diversity in leaf serrate or pinnate dissection patterns. In Arabidopsis thaliana, the development of leaf serration requires the activity of the transcription factor CUC2. Does this regulator also work for leaf dissections of the Asteraceae plants? If so, how do the conserved regulatory 'tools' work differently to produce diverse leaf forms?
Seedling leaf morphology was observed, and morphogenesis of leaf serration or lobes was examined by scanning electron microscopy (SEM). NAM genes, orthologues of arabidopsis CUC2, were isolated from A. acuminata with serrate leaves and A. asiatica with three-pinnatisect leaves, respectively. By means of whole-mount in situ mRNA hybridization and two quantitative gene expression assays, the droplet digital PCR (ddPCR) and quantitative real-time PCR (qPCR), expression patterns of the NAM genes during leaf dissection development were checked in both species for comparison.
For both species, the development of leaf dissection initiated when a leaf blade was about 300-400 µm long. In A. acuminata, in situ hybridization showed NAM expression signals at leaf margins where teeth are growing, or later on, in the sinuses of the teeth, whilst in A. asiatica, hybridization signals appear not only on leaf margins but further on the margins of leaf lobes. Both ddPCR and qPCR revealed a continuous decline of AacNAM expression from the early to the late developmental stages of a single leaf of A. acuminata, whereas a relatively long maintenance and fluctuation of AasNAM expression was seen in a leaf of A. asiatica.
Differential spatiotemporal patterns of NAM expression were found between the two yarrow species during development of leaf dissection. This study provides the first evidence for NAM activity in the development of leaf dissection of the Asteraceae plants, and demonstrates that leaf form diversity is correlated to the altered NAM expression dynamic.
理解物种多样性与表型发育进化之间的联系是进化生物学中的一个重要问题。在菊科蓍属（Achillea）中，锯齿或羽状分裂的叶片模式表现出很大的多样性。在拟南芥中，叶片锯齿的发育需要转录因子 CUC2 的活性。这个调节因子是否也适用于菊科植物的叶片分裂？如果是这样，这些保守的调节“工具”如何以不同的方式工作，从而产生不同的叶片形态？
观察幼苗叶片形态，并用扫描电子显微镜（SEM）检查叶片锯齿或裂片的形态发生。从具锯齿叶的 A. acuminata 和具三裂叶的 A. asiatica 中分别分离出 NAM 基因，它们是拟南芥 CUC2 的同源基因。通过整体原位 mRNA 杂交和两种定量基因表达分析，即液滴数字 PCR（ddPCR）和定量实时 PCR（qPCR），在两个物种中检查 NAM 基因在叶片分裂发育过程中的表达模式，以进行比较。
对于这两个物种，当叶片长约 300-400 µm 时，叶片分裂的发育就开始了。在 A. acuminata 中，原位杂交显示 NAM 表达信号出现在叶片边缘牙齿生长的地方，或者在后来的牙齿凹陷处，而在 A. asiatica 中，杂交信号不仅出现在叶片边缘，而且出现在叶片裂片的边缘。ddPCR 和 qPCR 都显示出 AacNAM 表达从 A. acuminata 单个叶片的早期发育阶段到晚期发育阶段连续下降，而 AasNAM 表达在 A. asiatica 叶片中则保持相对较长时间并波动。
在叶片分裂发育过程中，两个蓍属物种之间发现了 NAM 表达的时空差异模式。本研究首次为 NAM 活性在菊科植物叶片分裂发育中的作用提供了证据，并证明了叶片形态的多样性与 NAM 表达动态的改变有关。
