Chaiwanon Juthamas, Wang Zhi-Yong
Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA; Department of Biology, Stanford University, Stanford, CA 94305, USA.
Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA.
Curr Biol. 2015 Apr 20;25(8):1031-42. doi: 10.1016/j.cub.2015.02.046. Epub 2015 Apr 9.
The spatiotemporal balance between stem cell maintenance, proliferation, and differentiation determines the rate of root growth and is controlled by hormones, including auxin and brassinosteroid (BR). However, the spatial actions of BR and its interactions with auxin remain unclear in roots. Here, we show that oppositely patterned and antagonistic actions of BR and auxin maintain the stem cell balance and optimal root growth. We discover a pattern of low levels of nuclear-localized BR-activated transcription factor BZR1 in the stem cell niche and high BZR1 levels in the transition-elongation zone. This BZR1 pattern requires local BR catabolism and auxin synthesis, as well as BR signaling. Cell-type-specific expression of a constitutively active form of BZR1 confirms that the high and low levels of BZR1 are required for the normal cell behaviors in the elongation zone and quiescent center (QC), respectively. Comparison between BR-responsive, BZR1-targeted, auxin-responsive, and developmental zone-specific transcriptomes indicates that BZR1 mostly activates its target genes expressed in the transition-elongation zone, but represses genes in the QC and surrounding stem cells, and that BR and auxin have overall opposite effects on gene expression. Genetic and physiological interactions support that a balance between the antagonistic actions of BR and auxin is required for optimal root growth. These results demonstrate that the level and output specificity of BR signaling are spatially patterned and that, in contrast to their synergism in shoots, BR and auxin interact antagonistically in roots to control the spatiotemporal balance of stem cell dynamics required for optimal root growth.
干细胞维持、增殖和分化之间的时空平衡决定了根的生长速率，并受包括生长素和油菜素内酯（BR）在内的激素调控。然而，BR在根中的空间作用及其与生长素的相互作用仍不清楚。在这里，我们表明BR和生长素相反的模式及拮抗作用维持了干细胞平衡和最佳根生长。我们发现干细胞龛中核定位的BR激活转录因子BZR1水平低，而在过渡-伸长区BZR1水平高。这种BZR1模式需要局部BR分解代谢、生长素合成以及BR信号传导。组成型活性形式的BZR1的细胞类型特异性表达证实，伸长区和静止中心（QC）的正常细胞行为分别需要高水平和低水平的BZR1。BR反应性、BZR1靶向性、生长素反应性和发育区特异性转录组之间的比较表明，BZR1主要激活其在过渡-伸长区表达的靶基因，但抑制QC和周围干细胞中的基因，并且BR和生长素对基因表达总体上具有相反的影响。遗传和生理相互作用支持BR和生长素的拮抗作用之间的平衡是最佳根生长所必需的。这些结果表明，BR信号的水平和输出特异性在空间上是有模式的，并且与它们在地上部的协同作用相反，BR和生长素在根中相互拮抗，以控制最佳根生长所需的干细胞动态的时空平衡。
