Department of Agricultural Sciences, Viikki Plant Science Centre, University of Helsinki, P.O.Box 27, 00014, Helsinki, Finland.
J Plant Res. 2021 May;134(3):431-440. doi: 10.1007/s10265-021-01253-z. Epub 2021 Feb 4.
The Asteraceae plant family is characterized by inflorescences, called flower heads or capitula that may combine hundreds of individual florets into a single flower-like structure. The florets are arranged in a regular phyllotactic pattern with Fibonacci numbers of left- and right-winding spirals. Such a pattern may be disrupted due to physical constraints or by wounding occurring during the early meristem development. Recovery from wounding re-establishes patterning although the mechanisms have remained elusive. In this study, we applied Gerbera hybrida as a model system and established methods to conduct wounding experiments either with syringe needles or using laser ablation combined with live imaging of head meristems. By revisiting the historical experiments in sunflower, we conducted wounding to transgenic auxin reporter lines of gerbera and followed the recovery of cellular growth and meristem patterning. We show that wounding disrupted the expression of the gerbera CLAVATA3 (GhCLV3) gene that marks the undifferentiated meristematic region and led to de novo re-initiation of patterning at the wound margin. During the recovery growth, three to five layers of elongated cells showing periclinal cell division planes and lacking auxin signal were formed at the wound rim. DR5 auxin signal was shown to localize and form regularly spaced maxima in a distance from the wound rim. Consequently, spiral pattern of contact parastichies was re-established by stacking of new auxin maxima on top of the previous ones. The developed methods facilitate future studies on understanding the molecular mechanisms of de novo patterning of meristems.
菊科植物的特征是花序，称为头状花序或头状花序，它可以将数百个单独的小花组合成一个单一的花状结构。小花按照斐波那契数列的左旋和右旋螺旋排列。这种模式可能会因物理限制或在早期分生组织发育过程中受伤而中断。尽管机制仍不清楚，但受伤后的恢复会重新建立模式。在这项研究中，我们以杂种非洲菊为模型系统，建立了使用注射器针或激光消融结合头部分生组织的实时成像进行创伤实验的方法。通过重新审视向日葵的历史实验，我们对非洲菊的转基因生长素报告线进行了创伤处理，并观察了细胞生长和分生组织模式恢复的情况。我们表明，创伤破坏了标志未分化分生组织区域的非洲菊 CLAVATA3（GhCLV3）基因的表达，并导致在创伤边缘重新开始图案形成。在恢复生长过程中，在创伤边缘形成了三到五层伸长细胞，这些细胞表现出垂周细胞分裂面，并且缺乏生长素信号。DR5 生长素信号被证明在距创伤边缘一定距离处定位并形成规则间隔的最大值。因此，通过将新的生长素最大值叠加在前一个生长素最大值上，接触对生的螺旋模式得以重新建立。所开发的方法有助于未来研究理解分生组织从头开始的图案形成的分子机制。
