Micro RNA s and new biotechnological tools for its modulation and improving stress tolerance in plants

Summary Micro RNA s (mi RNA s) modulate the abundance and spatial–temporal accumulation of target mRNA s and indirectly regulate several plant processes. Transcriptional regulation of the genes encoding mi RNA s ( MIR genes) can be activated by numerous transcription factors, which themselves are regulated by other mi RNA s. Fine‐tuning of MIR genes or mi RNA s is a powerful biotechnological strategy to improve tolerance to abiotic or biotic stresses in crops of economic importance. Current approaches for mi RNA fine‐tuning are based on the down‐ or up‐regulation of MIR gene transcription and the use of genetic engineering tools to manipulate the final concentration of these mi RNA s in the cytoplasm. Transgenesis, cisgenesis, intragenesis, artificial MIR genes, endogenous and artificial target mimicry, MIR genes editing using Meganucleases, ZNF proteins, TALEN s and CRISPR /Cas9 or CRISPR /Cpf1, CRISPR / dC as9 or dC pf1, CRISPR 13a, topical delivery of mi RNA s and epigenetic memory have been successfully explored to MIR gene or mi RNA modulation and improve agronomic traits in several model or crop plants. However, advantages and drawbacks of each of these new biotechnological tools ( NBT s) are still not well understood. In this review, we provide a brief overview of the biogenesis and role of mi RNA s in response to abiotic or biotic stresses, we present critically the main NBT s used for the manipulation of MIR genes and mi RNA s, we show current efforts and findings with the MIR genes and mi RNA s modulation in plants, and we summarize the advantages and drawbacks of these NBT s and provide some alternatives to overcome. Finally, challenges and future perspectives to mi RNA modulating in important crops are also discussed.