Malamy J E, Ryan K S
Department of Molecular Genetics and Cell Biology, University of Chicago, R312 J.F. Knapp Center, Chicago, IL 60637, USA.
Plant Physiol. 2001 Nov;127(3):899-909.
Plant morphology is dramatically influenced by environmental signals. The growth and development of the root system is an excellent example of this developmental plasticity. Both the number and placement of lateral roots are highly responsive to nutritional cues. This indicates that there must be a signal transduction pathway that interprets complex environmental conditions and makes the "decision" to form a lateral root at a particular time and place. Lateral roots originate from differentiated cells in adult tissues. These cells must reenter the cell cycle, proliferate, and redifferentiate to produce all of the cell types that make up a new organ. Almost nothing is known about how lateral root initiation is regulated or coordinated with growth conditions. Here, we report a novel growth assay that allows this regulatory mechanism to be dissected in Arabidopsis. When Arabidopsis seedlings are grown on nutrient media with a high sucrose to nitrogen ratio, lateral root initiation is dramatically repressed. Auxin localization appears to be a key factor in this nutrient-mediated repression of lateral root initiation. We have isolated a mutant, lateral root initiation 1 (lin1), that overcomes the repressive conditions. This mutant produces a highly branched root system on media with high sucrose to nitrogen ratios. The lin1 phenotype is specific to these growth conditions, suggesting that the lin1 gene is involved in coordinating lateral root initiation with nutritional cues. Therefore, these studies provide novel insights into the mechanisms that regulate the earliest steps in lateral root initiation and that coordinate plant development with the environment.
植物形态受环境信号的影响极大。根系的生长和发育就是这种发育可塑性的一个绝佳例子。侧根的数量和着生位置对营养信号高度敏感。这表明必然存在一条信号转导途径，能够解读复杂的环境条件，并“决定”在特定的时间和位置形成侧根。侧根起源于成熟组织中的分化细胞。这些细胞必须重新进入细胞周期，进行增殖，并再次分化，以产生构成新器官的所有细胞类型。关于侧根起始如何被调控或与生长条件协调，我们几乎一无所知。在此，我们报告一种新的生长测定方法，该方法能够在拟南芥中剖析这种调控机制。当拟南芥幼苗在蔗糖与氮比例高的营养培养基上生长时，侧根起始受到显著抑制。生长素定位似乎是这种营养介导的侧根起始抑制中的一个关键因素。我们分离出了一个突变体——侧根起始1（lin1），它能克服这种抑制条件。该突变体在蔗糖与氮比例高的培养基上产生高度分支的根系。lin1表型对这些生长条件具有特异性，这表明lin1基因参与将侧根起始与营养信号协调起来。因此，这些研究为调控侧根起始最早步骤以及使植物发育与环境协调的机制提供了新的见解。
