Endogenous and synthetic microRNAs stimulate simultaneous, efficient, and localized regulation of multiple targets in diverse species.

Department of Plant Sciences, Weizman Institute of Science, Rehovot, 76100, Israel.
The Plant Cell (Impact Factor: 9.25). 06/2006; 18(5):1134-51. DOI: 10.1105/tpc.105.040725
Source: PubMed

ABSTRACT Recent studies demonstrated that pattern formation in plants involves regulation of transcription factor families by microRNAs (miRNAs). To explore the potency, autonomy, target range, and functional conservation of miRNA genes, a systematic comparison between plants ectopically expressing pre-miRNAs and plants with corresponding multiple mutant combinations of target genes was performed. We show that regulated expression of several Arabidopsis thaliana pre-miRNA genes induced a range of phenotypic alterations, the most extreme ones being a phenocopy of combined loss of their predicted target genes. This result indicates quantitative regulation by miRNA as a potential source for diversity in developmental outcomes. Remarkably, custom-made, synthetic miRNAs vectored by endogenous pre-miRNA backbones also produced phenocopies of multiple mutant combinations of genes that are not naturally regulated by miRNA. Arabidopsis-based endogenous and synthetic pre-miRNAs were also processed effectively in tomato (Solanum lycopersicum) and tobacco (Nicotiana tabacum). Synthetic miR-ARF targeting Auxin Response Factors 2, 3, and 4 induced dramatic transformations of abaxial tissues into adaxial ones in all three species, which could not cross graft joints. Likewise, organ-specific expression of miR165b that coregulates the PHABULOSA-like adaxial identity genes induced localized abaxial transformations. Thus, miRNAs provide a flexible, quantitative, and autonomous platform that can be employed for regulated expression of multiple related genes in diverse species.

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    ABSTRACT: Artificial microRNAs (amiRNAs) and synthetic trans-acting small interfering RNAs (syn-tasiRNAs) are used for small RNA-based, specific gene silencing or knockdown in plants. Current methods to generate amiRNA or syn-tasiRNA constructs are not well adapted for cost-effective, large-scale production, or for multiplexing to specifically suppress multiple targets. Here we describe simple, fast and cost-effective methods with high-throughput capability to generate amiRNA and multiplexed syn-tasiRNA constructs for efficient gene silencing in Arabidopsis and other plant species. AmiRNA or syn-tasiRNA inserts resulting from the annealing of two overlapping and partially complementary oligonucleotides are ligated directionally into a zero background BsaI/ccdB ('B/c')-based expression vector. B/c vectors for amiRNA and syn-tasiRNA cloning and expression contain a modified version of Arabidopsis MIR390a or TAS1c precursors, respectively, in which a fragment of the endogenous sequence was substituted by a ccdB cassette. Several amiRNA and syn-tasiRNA sequences designed to target one or more endogenous genes were validated in transgenic plants that a) exhibited the expected phenotypes predicted by loss of target gene function, b) accumulated high levels of accurately processed amiRNAs or syn-tasiRNAs, and c) had reduced levels of the corresponding target RNAs.
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