Mini Review MicroRNA-mediated signaling involved in plant root development Yijun Meng a,b , Xiaoxia Ma b , Dijun Chen a , Ping Wu b, * , Ming Chen a,b, * a Department of Bioinformatics, College of Life Sciences, Zhejiang University, Hangzhou 310058, PR China b State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310058, PR China article info Article history: Received 26 January 2010 Available online 6 February 2010 Keywords: MicroRNAs Signal interactions Feedback circuit Root development Arabidopsis Rice abstract MicroRNA (miRNA), recently recognized as a critical post-transcriptional modulator of gene expression, is involved in numerous biological processes in both animals and plants. Although eudicots and monocots, such as the model plants Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), possess distinct root systems, several homologous miRNA families are reported to be involved in root growth control in both plants. Consistent with recent notion that numerous signaling pathways are implicated in root develop- ment, these miRNAs are implicated in auxin signaling, nutrition metabolism, or stress response and have potential role in mediating the signal interactions. However, a recapitulative representation of these results is especially desired. This review provides a global view of the involvement of miRNAs in root development focusing on the two plants, Arabidopsis and rice. Based on current research advances, sev- eral innovative mechanisms of miRNA transcription, feedback regulatory circuit between miRNAs and transcription factors (TFs), and miRNA-mediated signal interactions are also discussed. Ó 2010 Elsevier Inc. All rights reserved. Introduction As the underground organ of terrestrial plants, the root is an indispensable component for plant survival. Root systems hold the plant upright, absorb water and nutrition for plant growth and development, produce the hormone cytokinin, and generate secondary metabolites involved in microorganism symbiosis or pathogen defense. A subtle change in the root systems of crops will greatly affect the yield. Recent research advances have broadened our understanding of the novel mechanisms of root development under various growth conditions. Besides a number of essential protein-coding genes [1–6], several miRNAs were reported to be implicated in root development modulation [7–9], reinforcing the growing awareness that miRNAs play pivotal roles in many bio- chemical or biophysical processes in planta. Intriguingly, several homologous miRNA families and conserved miRNA-mediated pathways involved in root development are shared by Arabidopsis and rice, although each plant has quite distinguishable root architecture, that is, tap root systems and fibrous root systems, respectively. In this review, we provide a global vision of miRNA- mediated root development integrating auxin, nutrition, and stress signaling pathways in Arabidopsis and rice based on current understandings of this research area. The updated issues on miRNA transcription and miRNA-mediated signal interactions are also raised and discussed here. MicroRNAs involved in auxin signaling Auxin signaling is one of the most intensively studied pathways mediated by miRNAs in plants. Several miRNA families, such as miR160, miR164, miR167, and miR390, were demonstrated to be involved in root cap formation, lateral root development, or adventitious rooting through the auxin signal further transduced by their downstream ARF (auxin response factor) targets (Fig. 1 and Table 1). Based on our experimental results ([13] and unpub- lished data) certain miRNAs playing potential roles in root cap formation or adventitious rooting in rice are also discussed. miR160 The miR160 family was first reported to be essential for root cap formation in Arabidopsis [9]. miR160 exerts its regulatory effect on root tip growth and gravity sensing through the ARF10- and ARF16- mediated downstream pathways, and both ARFs are targeted by miR160 in vivo. Although functionally redundant, both ARF10 and ARF16 are indispensable for root cap development in Arabidopsis. Our transgenic result demonstrates that overexpression of rice miR160 will cause serious root cap defect in rice (unpublished re- sult), although specific downstream ARF(s) or other target families need to be validated. In addition, miR160 was suggested to have a role in promoting lateral root production in Arabidopsis through 0006-291X/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2010.01.129 * Corresponding authors. Address: Department of Bioinformatics, College of Life Sciences, Zhejiang University, Zijingang Campus, Yu Hang Tang Road 388#, Hangzhou 310058, PR China. Fax: +86 571 88206613 (M. Chen); fax: +86 571 88206617 (P. Wu). E-mail addresses: clspwu@zju.edu.cn (P. Wu), mchen@zju.edu.cn (M. Chen). Biochemical and Biophysical Research Communications 393 (2010) 345–349 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc