Overexpression of miR166/165 down-regulates target HD - ZIP IIIs and promotes root growth by enhancing cell division and meristematic activity, whereas overexpression of HD - ZIP IIIs inhibits root growth in Arabidopsis thaliana. Post-embryonic growth of higher plants is maintained by active meristems harbouring undifferentiated cells. Shoot and root apical meristems (SAM and RAM) utilize both similar and distinct signalling mechanisms for their maintenance in Arabidopsis thaliana. An important regulatory role in this context has the interaction of microRNAs with their target mRNAs, mostly encoding transcription factors. One class of microRNA166/165 (miR166/165) has been implicated in the maintenance of SAM and vascular patterning. Here, we show that miR166/165 plays an important role in root growth also by negatively regulating its target transcripts, HD-ZIP IIIs, in the RAM. While overexpression of miR166 promotes RAM activity, overexpression of its targets reduces RAM activity. These results reveal a conserved role of miR166/165 in the maintenance of SAM and RAM activity in A. thaliana.

中文翻译：

---

microRNA166/165 的平衡活性及其来自 III 类同源域-亮氨酸拉链家族的目标转录本调节拟南芥的根生长。

miR166/165 的过表达下调靶标 HD-ZIP IIIs 并通过增强细胞分裂和分生组织活性促进根生长，而 HD-ZIP IIIs 的过表达抑制拟南芥的根生长。高等植物的胚后生长由含有未分化细胞的活性分生组织维持。芽和根尖分生组织（SAM 和 RAM）利用相似和不同的信号机制在拟南芥中维持它们。在这种情况下，一个重要的调节作用是 microRNA 与其目标 mRNA 的相互作用，主要是编码转录因子。一类 microRNA166/165 (miR166/165) 与 SAM 和血管模式的维持有关。这里，我们表明 miR166/165 通过在 RAM 中负调节其目标转录物 HD-ZIP IIIs 在根生长中发挥重要作用。虽然 miR166 的过表达会促进 RAM 活性，但其靶标的过表达会降低 RAM 活性。这些结果揭示了 miR166/165 在维持拟南芥 SAM 和 RAM 活性中的保守作用。