Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Ave., Cambridge, MA, 02138, USA.
Department of Biological Sciences, California State University Sacramento, 6000 J St., Sacramento, CA, 95819, USA.
Am J Bot. 2022 Sep;109(9):1360-1381. doi: 10.1002/ajb2.16046. Epub 2022 Sep 14.
Determining the developmental programs underlying morphological variation is key to elucidating the evolutionary processes that generated the stunning biodiversity of the angiosperms. Here, we characterized the developmental and transcriptional dynamics of the elaborate petal nectar spur of Aquilegia (columbine) in species with contrasting pollination syndromes and spur morphologies.
We collected petal epidermal cell number and length data across four Aquilegia species, two with short, curved nectar spurs of the bee-pollination syndrome and two with long, straight spurs of the hummingbird-pollination syndrome. We also performed RNA-seq on A. brevistyla (bee) and A. canadensis (hummingbird) distal and proximal spur compartments at multiple developmental stages. Finally, we intersected these data sets with a previous QTL mapping study on spur length and shape to identify new candidate loci.
The differential growth between the proximal and distal surfaces of curved spurs is primarily driven by differential cell division. However, independent transitions to straight spurs in the hummingbird syndrome have evolved by increasing differential cell elongation between spur surfaces. The RNA-seq data reveal these tissues to be transcriptionally distinct and point to auxin signaling as being involved with the differential cell elongation responsible for the evolution of straight spurs. We identify several promising candidate genes for future study.
Our study, taken together with previous work in Aquilegia, reveals the complexity of the developmental mechanisms underlying trait variation in this system. The framework we established here will lead to exciting future work examining candidate genes and processes involved in the rapid radiation of the genus.
确定形态变异背后的发育程序是阐明产生被子植物惊人生物多样性的进化过程的关键。在这里，我们描述了具有不同授粉综合征和距状形态的 Aquilegia（耧斗菜属）中精致花瓣蜜腺距的发育和转录动态。
我们在四个 Aquilegia 物种中收集了花瓣表皮细胞数量和长度数据，其中两个具有蜜蜂授粉综合征的短而弯曲的蜜腺距，两个具有蜂鸟授粉综合征的长而直的距。我们还在多个发育阶段对 A. brevistyla（蜜蜂）和 A. canadensis（蜂鸟）远侧和近侧距进行了 RNA-seq。最后，我们将这些数据集与先前关于距长和形状的 QTL 映射研究进行了交叉，以鉴定新的候选基因座。
弯曲距的近端和远端表面之间的差异生长主要是由差异细胞分裂驱动的。然而，蜂鸟综合征中独立向直距的转变是通过增加距表面之间的差异细胞伸长来进化的。RNA-seq 数据表明这些组织在转录上是不同的，并指出生长素信号参与了导致直距进化的差异细胞伸长。我们确定了几个有前途的候选基因，以供进一步研究。
我们的研究与 Aquilegia 之前的工作一起，揭示了该系统中性状变异背后的发育机制的复杂性。我们在这里建立的框架将为未来研究涉及候选基因和过程的快速辐射的属提供令人兴奋的工作。
