BackgroundWRKY genes, as the most pivotal transcription factors in plants, play the indispensable roles in regulating various physiological processes, including plant growth and development as well as in response to stresses. Broomcorn millet is one of the most important crops in drought areas worldwide. However, the WRKY gene family in broomcorn millet remains unknown.ResultsA total of 32 PmWRKY genes were identified in this study using computational prediction method. Structural analysis found that PmWRKY proteins contained a highly conserved motif WRKYGQK and two common variant motifs, namely WRKYGKK and WRKYGEK. Phylogenetic analysis of PmWRKYs together with the homologous genes from the representative species could classify them into three groups, with the number of 1, 15, and 16, respectively. Finally, the transcriptional profiles of these 32 PmWRKY genes in various tissues or under different abiotic stresses were systematically investigated using qRT-PCR analysis. Results showed that the expression level of 22 PmWRKY genes varied significantly under one or more abiotic stress treatments, which could be defined as abiotic stress-responsive genes.ConclusionsThis was the first study to identify the organization and transcriptional profiles of PmWRKY genes, which not only facilitates the functional analysis of the PmWRKY genes, and also lays the foundation to reveal the molecular mechanism of stress tolerance in this important crop.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2677-3) contains supplementary material, which is available to authorized users.

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.

ABSTRACT. Brachypodium distachyon has been proposed as a new model for the temperate grass because it is related to the major cereal grain species (such as wheat, barley, oat, maize, rice, and sorghum) and many forage and turf species. In this study, a multivariate statistical analysis was performed to investigate the characteristics of codon bias and the main factors affecting synonymous codon usage in Brachypodium. We found that lowand high-GC content genes with different codon usage occur frequently in the genome. The results of neutrality, correspondence, and correlation analyses indicated that mutational pressure and selective constraint were the main factors in shaping codon usage. Coding sequence length and the hydrophobicity of each protein were also identified as influences on codon usage bias, although their effect was minor. In addition, 27 codons, defined as "optimal codons", might provide useful information for gene engineering, gene prediction, and molecular evolution studies.

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