Mironova Victoria V, Omelyanchuk Nadezda A, Yosiphon Guy, Fadeev Stanislav I, Kolchanov Nikolai A, Mjolsness Eric, Likhoshvai Vitaly A
Institute of Cytology and Genetics, SB RAS, Lavrentyeva 10, Novosibirsk, Russia.
BMC Syst Biol. 2010 Jul 21;4:98. doi: 10.1186/1752-0509-4-98.
In plant roots, auxin is critical for patterning and morphogenesis. It regulates cell elongation and division, the development and maintenance of root apical meristems, and other processes. In Arabidopsis, auxin distribution along the central root axis has several maxima: in the root tip, in the basal meristem and at the shoot/root junction. The distal maximum in the root tip maintains the stem cell niche. Proximal maxima may trigger lateral or adventitious root initiation.
We propose a reflected flow mechanism for the formation of the auxin maximum in the root apical meristem. The mechanism is based on auxin's known activation and inhibition of expressed PIN family auxin carriers at low and high auxin levels, respectively. Simulations showed that these regulatory interactions are sufficient for self-organization of the auxin distribution pattern along the central root axis under varying conditions. The mathematical model was extended with rules for discontinuous cell dynamics so that cell divisions were also governed by auxin, and by another morphogen Division Factor which combines the actions of cytokinin and ethylene on cell division in the root. The positional information specified by the gradients of these two morphogens is able to explain root patterning along the central root axis.
We present here a plausible mechanism for auxin patterning along the developing root, that may provide for self-organization of the distal auxin maximum when the reverse fountain has not yet been formed or has been disrupted. In addition, the proximal maxima are formed under the reflected flow mechanism in response to periods of increasing auxin flow from the growing shoot. These events may predetermine lateral root initiation in a rhyzotactic pattern. Another outcome of the reflected flow mechanism - the predominance of lateral or adventitious roots in different plant species - may be based on the different efficiencies with which auxin inhibits its own transport in different species, thereby distinguishing two main types of plant root architecture: taproot vs. fibrous.
在植物根系中，生长素对于模式形成和形态发生至关重要。它调节细胞伸长和分裂、根尖分生组织的发育与维持以及其他过程。在拟南芥中，生长素沿主根轴的分布有多个最大值：在根尖、基部分生组织以及茎/根连接处。根尖处的远端最大值维持干细胞龛。近端最大值可能触发侧根或不定根的起始。
我们提出了一种用于根尖分生组织中生长素最大值形成的反射流机制。该机制基于生长素在低水平和高水平时分别对已表达的PIN家族生长素载体的已知激活和抑制作用。模拟表明，这些调节相互作用足以在不同条件下沿主根轴自组织生长素分布模式。数学模型通过不连续细胞动力学规则进行了扩展，使得细胞分裂也受生长素以及另一种形态发生素“分裂因子”的控制，“分裂因子”结合了细胞分裂素和乙烯对根中细胞分裂的作用。这两种形态发生素梯度所指定的位置信息能够解释沿主根轴的根系模式形成。
我们在此提出了一种沿发育中根系的生长素模式形成的合理机制，当反向喷泉尚未形成或已被破坏时，该机制可能实现远端生长素最大值的自组织。此外，近端最大值是在反射流机制下响应来自生长茎尖生长素流量增加的时期而形成的。这些事件可能以向根性模式预先决定侧根起始。反射流机制的另一个结果——不同植物物种中侧根或不定根的优势——可能基于生长素在不同物种中抑制自身运输的不同效率，从而区分出两种主要的植物根系结构类型：直根系与须根系。
