Originally isolated as a result of its ability to interact with the movement protein of Tomato spotted wilt virus in a yeast two-hybrid system, the 4/1 protein is proving to be an excellent tool for studying intracellular protein trafficking and intercellular communication. Expression of 4/1 in vivo is tightly regulated, first appearing in the veins of the cotyledon and later in the vasculature of the leaf and stem in association with the xylem parenchyma and phloem parenchyma. Structural studies indicate that 4/1 proteins contain as many as 5 coiled-coil (CC) domains; indeed, the highest level of sequence identity among 4/1 proteins involves their C-terminal CC domains, suggesting that protein-protein interaction is important for biological function. Recent data predict that the tertiary structure of this C-terminal CC domain is strikingly similar to that of yeast protein She2p; furthermore, like She2p, 4/1 protein exhibits RNA-binding activity, and mutational analysis has shown that the C-terminal CC domain is responsible for RNA binding. The 4/1 protein contains a nuclear export signal. Additional microscopy studies involving leptomycin and computer prediction suggest the presence of a nuclear localization signal as well.

Members of the genus Tobamovirus represent one of the best-characterized groups of plant positive, single stranded RNA viruses. Previous studies have shown that genomes of some tobamoviruses contain not only genes coding for coat protein, movement protein, and the cistron coding for different domains of RNA-polymerase, but also a gene, named ORF6, coding for a poorly conserved small protein. The amino acid sequences of ORF6 proteins encoded by different tobamoviruses are highly divergent. The potential role of ORF6 proteins in replication of tobamoviruses still needs to be elucidated. In this study, using biochemical and immunological methods, we have shown that ORF6 peptide is accumulated after infection in case of two isolates of Tobacco mosaic virus strain U1 (TMV-U1 common and TMV-U1 isolate A15). Unlike virus particles accumulating in the cytoplasm, the product of the ORF6 gene is found mainly in nuclei, which correlates with previously published data about transient expression of ORF6 isolated from TMV-U1. Moreover, we present new data showing the presence of ORF6 genes in genomes of several tobamoviruses. For example, in the genomes of other members of the tobamovirus subgroup 1, including Rehmannia mosaic virus, Paprika mild mottle virus, Tobacco mild green mosaic virus, Tomato mosaic virus, Tomato mottle mosaic virus, and Nigerian tobacco latent virus, sequence comparisons revealed the existence of a similar open reading frame like ORF6 of TMV.

MicroRNAs (miRNAs) are small regulatory RNAs that are expressed in a tissue-specific manner during the development of plants and animals. The genes of miRNAs have been found to produce the following two products: (i) primary transcripts of these genes (pri-miRNA) are processed to give rise to mature miRNA, and (ii) in some cases, the pri-miRNA molecules can be translated to form small peptides, named as miPEPs. Gene silencing by artificial microRNAs (amiRNAs) is one of the potential crucial methods for the regulation of desired genes to improve horticultural plants. Likewise, external application of chemically synthesized miPEPs may help plants to resist biotic/abiotic stresses and grow faster. These potent and reliable derivatives of miRNA genes can be applied for improving useful traits in crop plants. This review summarizes the progress in research on the artificial gene derivatives involved in regulating plant development, virus and pest diseases, and abiotic stress resistance pathways. We also briefly discuss the molecular mechanisms of relevant target genes for future research on breeding in plants. In general, this review may be useful to researchers who are implementing amiRNA and miPEP for accelerating breeding programs and developmental studies in crop plants.

MicroRNAs are endogenous, small non-coding RNAs that regulate gene expression at the post-transcriptional level by cleaving target mRNAs. Mature microRNAs are products of the processing of their primary transcripts (pri-miRNAs). Now, it has been discovered that the products of the translation of some plant pri-miRNAs are peptide molecules (miPEP). These peptides have the capacity to physically interact with their open reading frames (ORFs) in the transcribed pri-miRNAs and, thus, positively regulate the accumulation of these RNAs and the corresponding mature microRNAs. Most conserved microRNAs play an important role in plants development and their response to stress. In this work, we obtained transgenic Physcomitrium patens moss plants containing Brassica oleracea miPEP156a ORF in the genome under the control of a strong 35S cauliflower mosaic virus promoter and analyzed the effect of the exogenous peptide on the transcription of this ORF in the protonemata of two transgenic moss lines. It turned out that the chemically synthesized peptide miPEP156a increases the accumulation of its own mRNA during moss culture growth, as was previously shown in studies by foreign researchers and in our own work for a number of peptides in monocotyledonous and dicotyledonous plants. These findings confirm that pri-miRNA regions that are located outside the coding region of the peptide are not required for transcriptional activation. Moreover, we have also succeeded in showing that the presence of a specific promoter of the microRNA gene does not affect the phenomenon of transcription activation; this phenomenon per se is not species-specific and is observed in transgenic plants, regardless of the origin of the miPEP.