BackgroundMitogen-activated protein kinase kinase kinases (MAPKKKs) are the important components of MAPK cascades, which play the crucial role in plant growth and development as well as in response to diverse stresses. Although this family has been systematically studied in many plant species, little is known about MAPKKK genes in wheat (Triticum aestivum L.), especially those involved in the regulatory network of stress processes.ResultsIn this study, we identified 155 wheat MAPKKK genes through a genome-wide search method based on the latest available wheat genome information, of which 29 belonged to MEKK, 11 to ZIK and 115 to Raf subfamily, respectively. Then, chromosome localization, gene structure and conserved protein motifs and phylogenetic relationship as well as regulatory network of these TaMAPKKKs were systematically investigated and results supported the prediction. Furthermore, a total of 11 homologous groups between A, B and D sub-genome and 24 duplication pairs among them were detected, which contributed to the expansion of wheat MAPKKK gene family. Finally, the expression profiles of these MAPKKKs during development and under different abiotic stresses were investigated using the RNA-seq data. Additionally, 10 tissue-specific and 4 salt-responsive TaMAPKKK genes were selected to validate their expression level through qRT-PCR analysis.ConclusionsThis study for the first time reported the genome organization, evolutionary features and expression profiles of the wheat MAPKKK gene family, which laid the foundation for further functional analysis of wheat MAPKKK genes, and contributed to better understanding the roles and regulatory mechanism of MAPKKKs in wheat.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2993-7) contains supplementary material, which is available to authorized users.

SummarySeveral varieties of small RNAs including microRNAs (miRNAs) and small interfering RNAs (siRNAs) are generated in plants to regulate development, genome stability and response to adverse environments. Phased siRNA (phasiRNA) is a type of secondary siRNA that is processed from a miRNA‐mediated cleavage of RNA transcripts, increasing silencing efficiency or simultaneously suppressing multiple target genes. Trans‐acting siRNAs (ta‐siRNAs) are a particular class of phasiRNA produced from noncoding transcripts that silence targets in trans. It was originally thought that ‘one‐hit’ and ‘two‐hit’ models were essential for processing distinct TAS precursors; however, a single hit event was recently shown to be sufficient at triggering all types of ta‐siRNAs. This review discusses the findings about biogenesis, targeting modes and regulatory networks of plant ta‐siRNAs. We also summarize recent advances in the generation of other phasiRNAs and their possible biological benefits to plants.

Long non-coding RNAs (lncRNAs) are gene regulators that have vital roles in development and adaptation to the environment in eukaryotes. However, the structural and evolutionary analyses of plant lncRNAs are limited. In this study, we performed an analysis of lncRNAs in five monocot and five dicot species. Our results showed that plant lncRNA genes were generally shorter and had fewer exons than protein-coding genes. The numbers of lncRNAs were positively correlated with the numbers of protein-coding genes in different plant species, despite a high range of variation. Sequence conservation analysis showed that the majority of lncRNAs had high sequence conservation at the intra-species and sub-species levels, reminiscent of protein-coding genes. At the inter-species level, a subset of lncRNAs were highly diverged at the nucleotide level, but conserved by position. Interestingly, we found that plant lncRNAs have identical splicing signals, and those which can form precursors or targets of miRNAs have a conservative identity in different species. We also revealed that most of the lowly expressed lncRNAs were tissue-specific, while those highly conserved were constitutively transcribed. Meanwhile, we characterized a subset of rice lncRNAs that were co-expressed with their adjacent protein-coding genes, suggesting they may play cis-regulatory roles. These results will contribute to understanding the biological significance and evolution of lncRNAs in plants.

Comparative chloroplast genome analysis presents new opportunities for performing molecular phylogeny studies and revealing the significant evolutionary features in higher plants, which has been widely documented from conifers to grass family. However, a systematic analysis of chloroplast genomes in Asteraceae family has not been conducted up to now. In this study, we compared and analyzed the gene content, genomic organization, and RNA editing sites of eight representative Asteraceae chloroplast genomes. Results showed that Asteraceae chloroplast had relatively conservative gene content. No gain or loss events occurred in the proteincoding genes, while some differences were found to be present in the gene structure and transfer RNA (tRNA) abundance. Genome structure analysis found some Asteraceae-specific or species-specific structure variations, and sequence rearrangement events were present in these genomes, suggesting specific evolutionary processes have occurred in this family. Some DNA regions containing parsimony-informative characters higher than 5 % were also identified, which could be used as the new molecular markers for phylogenetic analysis and plant identification of Asteraceae species. Furthermore, RNA editing in these genomes was investigated through computational analysis, and some species-specific sites were identified. Finally, phylogenetic analysis of 81 genes from 70 species supported the monophyly of the Asteraceae. Our study for the first time compared the organization, structure, and sequence divergence of eight Asteraceae chloroplast genomes, which will provide the valuable resource for molecular phylogeny of Asteraceae species and also facilitate the genetic and evolutionary studies in this family.