Abstract
MicroRNAs are short (19–24-nucleotide-long), non-coding RNA molecules. They downregulate gene expression by triggering the cleavage or translational inhibition of complementary mRNAs. Senescence is a stage of development following growth completion and is dependent on the expression of specific genes. MicroRNAs control the gene expression responsible for plant competence to answer senescence signals. Therefore, they coordinate the juvenile-to-adult phase transition of the whole plant, the growth and senescence phase of each leaf, age-related cellular structure changes during vessel formation, and remobilization of resources occurring during senescence. MicroRNAs are also engaged in the ripening and postharvest senescence of agronomically important fruits. Moreover, the hormonal regulation of senescence requires microRNA contribution. Environmental cues, such as darkness or drought, induce senescence-like processes in which microRNAs also play regulatory roles. In this review, we discuss recent findings concerning the role of microRNAs in the senescence of various plant species.
Highlights
MicroRNAs are 19–24-nucleotide-long, small, non-coding, single-stranded RNAs
We summarize the current knowledge on microRNA-regulated developmental processes leading to plant senescence
In tobacco (Nicotiana tabacum), microRNA156 overexpression causes the promotion of side shoots and lateral roots development [63]. These results indicate that microRNA156 is a master regulator of vegetative growth
Summary
MicroRNAs are 19–24-nucleotide-long, small, non-coding, single-stranded RNAs. MicroRNAs act at the post-transcriptional level, targeting specific mRNAs to trigger cleavage or translation inhibition. The degree of complementarity between a microRNA and its target mRNA determines whether the mRNA will be cleaved or its translation will be inhibited [1,2,3,4,5]. MicroRNAs and their function in gene expression have been further identified in many eukaryotic species, as well as in plants. Arabidopsis thaliana was the first plant specimen in which microRNAs were identified. The number of different microRNAs varies between plant species, and for A. thaliana and Oryza sativa it is 428 and 738, respectively [9,10]. The degree of microRNA conservation ranges from those conserved within the whole Viridiplantae clade to non-conserved species-specific molecules. The unicellular algae Chlamydomonas reinhardtii is to some extent exceptional, because the vast majority of its identified microRNAs are specific to algae, and only three microRNA species are found in liverworts [11,12]
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