Plant microRNAs: key regulators of root architecture and biotic interactions

Summary Plants have evolved a remarkable faculty of adaptation to deal with various and changing environmental conditions. In this context, the roots have taken over nutritional aspects and the root system architecture can be modulated in response to nutrient availability or biotic interactions with soil microorganisms. This adaptability requires a fine tuning of gene expression. Indeed, root specification and development are highly complex processes requiring gene regulatory networks involved in hormonal regulations and cell identity. Among the different molecular partners governing root development, micro RNA s (mi RNA s) are key players for the fast regulation of gene expression. mi RNA s are small RNA s involved in most developmental processes and are required for the normal growth of organisms, by the negative regulation of key genes, such as transcription factors and hormone receptors. Here, we review the known roles of mi RNA s in root specification and development, from the embryonic roots to the establishment of root symbioses, highlighting the major roles of mi RNA s in these processes. Contents Summary 22 I. Introduction 22 II. The roles of miRNAs in the specification of embryonic roots 24 III. The roles of miRNAs at the post‐embryonic root meristem (Fig. 2) 25 IV. The roles of miRNAs during lateral and adventitious root formation (Fig. 3) 27 V. The roles of miRNAs during root endosymbioses 29 VI. Concluding remarks and future perspectives 10 Acknowledgements 31 References 32