Development in plants is a continuous process during which new tissues and organs are formed all along its life cycle. Development involves the coordination of both time and space of complex cellular processes such as proliferation, expansion and differentiation following endogenous programmes and in response to environmental signals. Since their discovery in 2002, plant microRNAs (miRNAs), a class of small single-stranded regulatory ribonucleic acids (RNAs) have emerged as important nodes in regulatory networks controlling plant development. For instance, miRNAs play important roles for cell fate determination during the patterning of organs and contribute to the regulation of their growth. In addition, miRNAs integrate different signals to regulate the life cycle of plants. Finally, miRNAs appear as molecular links between environmental signals and plant development and may constitute levers to modify plant development in crops.
- miRNAs are essential for plant development as mutants affecting miRNA biogenesis or function are embryo lethal or show severe pleiotropic defects.
- miRNA precursors are mostly produced from independent genetic units and are processed into mature miRNAs via a complex core machinery.
- miRNAs can have different effects on the expression of their target genes, controlling their spatial pattern, their level of expression or the timing of their expression.
- miRNAs are regulating many different developmental processes, including pattern formation, morphogenesis and differentiation at all stages of a plant's life.
- Most of the miRNAs regulating plant development are evolutionary conserved and target evolutionary conserved transcription factors.
- miRNAs can act non-cell-autonomously, generating a mobile signal that contributes to pattern formation through the regulation of the expression pattern of their targets.
- miRNAs are integrated into complex regulatory networks and their expression is regulated by both endogenous and exogenous signals.