58 POJ 11(01):58-79 (2018) ISSN:1836-3644 doi: 10.21475/poj.11.01.18.pne1014 Dynamic roles of microRNAs in nutrient acquisition and plant adaptation under nutrient stress: A review Raheel Shahzad 1 *†, Putri Widyanti Harlina 2 †, Mohammed Ayaad 1,3 , Mohamed Ewas 1,4 , Elsayed Nishawy 1,4 , Shah Fahad 5 , Hizar Subthain 1 , Mohamed H. Amar 4 1 National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research, Huazhong Agricultural University, Wuhan 430070, China 2 Department of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China 3 Department of Plant Research, Radioisotopes Application Division, Nuclear Research Center of Atomic Energy Authority, Inshas, Egypt 4 Egyptian Deserts Gene Bank (EDGB), Genetic Resources Department, Desert Research Center (DRC), Cairo, Egypt 5 Department of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China †Raheel Shahzad and Putri Widyanti Harlina contributed equally to this work. *Corresponding author: raheel.shahzad@webmail.hzau.edu.cn Abstract A constant supply of soil nutrients is critical for the normal growth and development of plants. However, most environments are unstable and this variability depends on numerous factors that include availability of water content, pH, redox potential, an abundance of organic matter as well as microorganisms in soils. To overcome these hurdles and to maintain nutritional homeostasis, plants have evolved sophisticated systems for the continuous provision of soil nutrients necessary for their uninterrupted growth. In this pressing scenario, plant microRNAs (miRNAs) have emerged as a central regulator of nutrients uptake and transport during limited nutrient conditions. Numerous studies establish the intrinsic involvement of miRNAs and their immediate targets facilitating the core mechanisms related to nutrient homeostasis. In this review, we focus on global overview of miRNAs and their dynamic roles involved in keeping nutritional balance within the plants mediated via post-transcriptional regulation by transcript cleavage or translational inhibition of their target mRNAs. In addition, we have also focused on some of the forefront plant adaptations mediated by miRNAs during nutrient deficiency, such as root architecture modifications, transport channel modulation, long distance signaling and subsequent nutrient mobilization through phloem. Moreover, plant strategy to bring out such alterations is a highly perplexing mechanism that requires changes at large scale which involves coordinated regulation of miRNAs and plant hormones at multiple levels. Deciphering the underlying miRNAs-based mechanisms for streamlining nutrient uptake and transport would be a giant step towards solving this conundrum. Keywords: microRNAs, Nutrient acquisition, Mechanisms, Plant adaptation. Introduction Normal plant growth, development and yield extensively depend on constant supply of nutrients through the soil in any crop production system. There is a dynamic relationship of the plant’s nutritional status with plant susceptibility to various pathogens as well as abiotic environmental stresses in both intensive and integrated cropping systems. Plant nutrients play key functions critical for maintaining growth and development including structural components, cellular exchanges, osmotic regulations as well as biosynthesis of essential metabolites (Takehisa et al., 2013). MiRNAs are diverse regulatory molecules of small size and are considered chief controllers for the growth and development of various plants. Several miRNAs have been found to take part in diverse functions and fundamentally involved in numerous physiological events, such as stem cell proliferation, leaf and floral development, flowering initiation, tissue and organ buildup, as well as regulation of positive responses to various biotic and abiotic stresses (Willmann and Poethig, 2005; Sunkar et al., 2007; Zhou et al., 2012; Guo et al., 2013; Song et al., 2013; Wang B et al., 2014; Li and Zhang, 2016; Gao et al., 2016; Jian et al., 2016). Since miRNAs are involved in the regulation of essentially all cellular metabolic pathways, transformation of their biogenesis is of supreme importance for the maintenance of cellular homeostasis. MicroRNAs (miRNAs) are small noncoding RNAs 20–24 nucleotides long that control gene expression by promoting degradation or repressing translation of target mRNAs. Biogenesis of miRNA starts with MIRNA genes transcription directed by DNA dependent RNA polymerase II to form pri-miRNAs (Kim, 2005). Additionally, MIR promoters contain the TATA-box and cis-regulatory motifs, which explains the transcriptional regulation of MIR expression (Zhao and Li, 2013). Lack of mediator (a multi-subunit complex) disrupts the recruitment of of Pol II