Fang Tao, Motte Hans, Parizot Boris, Beeckman Tom
Department of Plant Biotechnology and Bioinformatics, Ghent University, Ghent, Belgium.
VIB Center for Plant Systems Biology, Ghent, Belgium.
Front Plant Sci. 2019 Feb 20;10:154. doi: 10.3389/fpls.2019.00154. eCollection 2019.
Angiosperms develop intensively branched root systems that are accommodated with the high capacity to produce plenty of new lateral roots throughout their life-span. Root branching can be dynamically regulated in response to edaphic conditions and provides the plants with a soil-mining potential. This highly specialized branching capacity has most likely been key in the colonization success of the present flowering plants on our planet. The initiation, formation and outgrowth of branching roots in Angiosperms are dominated by the plant hormone auxin. Upon auxin treatment root branching through the formation of lateral roots can easily be induced. In this study, we questioned whether this strong branching-inducing action of auxin is part of a conserved mechanism that was already active in the earliest diverging lineage of vascular plants with roots. In Selaginella, an extant representative species of this early clade of root forming plants, components of the canonical auxin signaling pathway are retrieved in its genome. Although we observed a clear physiological response and an indirect effect on root branching, we were not able to directly induce root branching in this species by application of different auxins. We conclude that the structural and developmental difference of the Selaginella root, which branches via bifurcation of the root meristem, or the absence of an auxin-mediated root development program, is most likely causative for the absence of an auxin-induced branching mechanism.
被子植物发育出高度分支的根系，这种根系具有在其整个生命周期中大量产生新侧根的高能力。根的分支可以根据土壤条件进行动态调节，并为植物提供挖掘土壤的潜力。这种高度专业化的分支能力很可能是当今地球上开花植物在定殖成功方面的关键因素。被子植物中分支根的起始、形成和生长主要受植物激素生长素的控制。经过生长素处理后，通过形成侧根很容易诱导根的分支。在本研究中，我们质疑生长素这种强烈的分支诱导作用是否是一种保守机制的一部分，这种机制在最早分化出有根维管植物的谱系中就已经发挥作用。在卷柏（Selaginella）中，这种早期形成根的植物类群的现存代表性物种，其基因组中检索到了经典生长素信号通路的成分。尽管我们观察到了明显的生理反应以及对根分支的间接影响，但通过施用不同的生长素，我们无法在该物种中直接诱导根分支。我们得出结论，卷柏根的结构和发育差异（通过根分生组织的分叉进行分支），或者缺乏生长素介导的根发育程序，很可能是导致缺乏生长素诱导分支机制的原因。
