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Horizontal gene transfer (HGT) describes the transmission of genetic material across species boundaries. HGT often occurs in microbic and eukaryotic genomes. However, the pathways by which HGTs occur in multicellular eukaryotes, especially in plants, are not well understood. We systematically summarized more than ten possible pathways for HGT. The intimate contact which frequently occurs in parasitism, symbiosis, pathogen, epiphyte, entophyte, and grafting interactions could promote HGTs between two species. Besides these direct transfer methods, genes can be exchanged with a vector as a bridge: possible vectors include pollen, fungi, bacteria, viruses, viroids, plasmids, transposons, and insects. HGT, especially when involving horizontal transfer of transposable elements, is recognized as a significant force propelling genomic variation and biological innovation, playing an important functional and evolutionary role in both eukaryotic and prokaryotic genomes. We proposed possible mechanisms by which HGTs can occur, which is useful in understanding the genetic information exchange among distant species or distant cellular components.

DNA‐based molecular markers play a significant role in gene mapping, genetic diversity analysis, germplasm evaluation and molecular marker‐assisted selection. A combination of desirable marker characteristics such as abundant polymorphism, good stability, ease of production and high efficiency is difficult to achieve when utilizing traditional molecular marker systems. MicroRNAs are a type of endogenous non‐coding RNAs prevalent in the genomes of many organisms. The high conservation of miRNA and pre‐miRNA sequences provides an opportunity to develop a novel molecular marker type. We downloaded 82 miRNA sequences from the Brassica miRBase database and designed 46 single miRNA‐based primers which could be randomly combined to generate primer pairs. A proportion of these primer pairs were validated for transferability and polymorphism using DNA from 16 varieties of six Brassica species. The percentage of polymorphic primer pairs were 28.1%, and the average polymorphism information content (PIC) value for the 34 primer pairs was 0.43. Good transferability was verified across species. These results indicate that miRNA‐based markers provide a novel genotyping technique with low costs, high efficiency, stability and good transferability.

Main conclusion This review will provide evidence for the indispensable function of these elements in regulating plant development and resistance to biotic and abiotic stresses, as well as their evolutionary role in facilitating plant adaptation.

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