Department of Biological Science, Florida State University, Tallahassee, FL, USA.
Plant Signal Behav. 2012 Mar;7(3):314-7. doi: 10.4161/psb.19118. Epub 2012 Mar 1.
SHORT-ROOT (SHR) is a key regulator of radial patterning and stem-cell renewal in the Arabidopsis root. Although SHR is expressed in the stele, its function in the vascular tissue was not recognized until recently. In shr, the protoxylem is missing due to the loss of expression of microRNA165A (miR165A) and microRNA166B (miR165B). shr is also defective in lateral root formation, but the mechanism remains unclear. To dissect the SHR developmental pathway, we recently have identified its direct targets at the genome scale by chromatin immunoprecipitation followed by microarray analysis (ChIP-chip). In further studies, we have shown that SHR regulates cytokinin homeostasis through cytokinin oxidase 3 and that this role of SHR is critical to vascular patterning in the root. In this communication we report that SHR also regulates miR165A and miR166B indirectly through its effect on cytokinin homeostasis. Although cytokinin is inhibitory to root growth, the root-apical-meristem defect in shr was not alleviated by reduction of endogenous cytokinin. These results together suggest that SHR regulates vascular patterning, but not root apical meristematic activity, through cytokinin homeostasis.
短根（SHR）是拟南芥根中辐射模式和干细胞更新的关键调节因子。尽管 SHR 在中柱中表达，但直到最近才认识到其在血管组织中的功能。在 shr 中，由于 microRNA165A（miR165A）和 microRNA166B（miR165B）表达的丧失，原木质部缺失。shr 也在侧根形成中出现缺陷，但机制尚不清楚。为了解剖 SHR 发育途径，我们最近通过染色质免疫沉淀和微阵列分析（ChIP-chip）在基因组范围内鉴定了其直接靶标。在进一步的研究中，我们表明 SHR 通过细胞分裂素氧化酶 3调节细胞分裂素稳态，并且 SHR 的这一作用对根中的血管模式至关重要。在本通讯中，我们报告 SHR 还通过其对细胞分裂素稳态的影响间接调节 miR165A 和 miR166B。尽管细胞分裂素抑制根的生长，但 shr 中根顶端分生组织的缺陷不能通过减少内源性细胞分裂素来缓解。这些结果共同表明，SHR 通过细胞分裂素稳态调节血管模式，但不调节根尖分生组织活性。
