MicroRNAs (miRNAs) are a class of endogenous RNAs that regulates the gene expression involved in various biological and metabolic processes. Barley is one of the most important cereal crops worldwide and is a model organism for genetic and genomic studies in Triticeae species. However, the miRNA research in barley has lagged behind other model species in grass family. To obtain more information of miRNA genes in barley, we sequenced a small RNA library created from a pool of equal amounts of RNA from four different tissues using Solexa sequencing. In addition to 126 conserved miRNAs (58 families), 133 novel miRNAs belonging to 50 families were identified from this sequence data set. The miRNA* sequences of 15 novel miRNAs were also discovered, suggesting the additional evidence for existence of these miRNAs. qRT-PCR was used to examine the expression pattern of six randomly selected miRNAs. Some miRNAs involved in drought and salt stress response were also identified. Furthermore, the potential targets of these putative miRNAs were predicted using the psRNATarget tools. Our results significantly increased the number of novel miRNAs in barley, which should be useful for further investigation into the biological functions and evolution of miRNAs in barley and other species.

Codon usage patterns of 23 Poaceae chloroplast genomes were analysed in this study. Neutrality analysis indicated that the codon usage patterns have significant correlations with GC12 and GC3 and also showed strong bias towards a high representation of NNA and NNT codons. The Nc-plot showed that although a large proportion of points follow the parabolic line of trajectory, several genes with low ENc values lie below the expected curve, suggesting that mutational bias played a major role in the codon biology of the Poaceae chloroplast genome. Parity Rule 2 plot analysis showed that T was used more frequently than A in all the genomes. Correspondence analysis of relative synonymous codon usage indicated that the first axis explained only a partial amount of variation of codon usage. Furthermore, the gene length and expression level were also found to drive codon usage variation. These findings revealed that besides natural selection, other factors might also exert some influences in shaping the codon usage bias in Poaceae chloroplast genomes. The optimal codons of these 23 genomes were also identified in this study.