Background: Allopolyploidy is widespread in angiosperms, and they can coordinate two or more different genomes through genetic and epigenetic modifications to exhibit stronger vigor and adaptability. To explore the changes in homologous gene expression patterns in the natural allotetraploid Brassica napus (A_nA_nC_nC_n) relative to its two diploid progenitors, B. rapa (A_rA_r) and B. oleracea (C_oC_o), after approximately 7500 years of domestication, the global gene pair expression patterns in four major tissues (stems, leaves, flowers and siliques) of these three species were analyzed using an RNA sequencing approach. Results: The results showed that the ‘transcriptomic shock’ phenomenon was alleviated in natural B. napus after approximately 7500 years of natural domestication, and most differentially expressed genes (DEGs) in B. napus were downregulated relative to those in its two diploid progenitors. The KEGG analysis indicated that three pathways related to photosynthesis were enriched in both comparison groups (A_nA_nC_nC_n vs A_rA_r and A_nA_nC_nC_n vs C_oC_o), and these pathways were all downregulated in four tissues of B. napus. In addition, homoeolog expression bias and expression level dominance (ELD) in B. napus were thoroughly studied through analysis of expression levels of 27,609 B. rapa-B. oleracea orthologous gene pairs. The overwhelming majority of gene pairs (an average of 86.7%) in B. napus maintained their expression pattern in two diploid progenitors, and approximately 78.1% of the gene pairs showed expression bias with a preference toward the A subgenome. Overall, an average of 48, 29.7 and 22.3% homologous gene pairs exhibited additive expression, ELD and transgressive expression in B. napus, respectively. The ELD bias varies from tissue to tissue; specifically, more gene pairs in stems and siliques showed ELD-A, whereas the opposite was observed in leaves and flowers. More transgressive upregulation, rather than downregulation, was observed in gene pairs of B. napus. Conclusions: In general, these results may provide a comprehensive understanding of the changes in homologous gene expression patterns in natural B. napus after approximately 7500 years of evolution and domestication and may enhance our understanding of allopolyploidy.

WUSCHEL-related homeobox (WOX) genes encoding plant-specific homeobox (HB) transcription factors play important roles in the growth and development of plants. To date, WOX genes has been identified and analyzed in many polyploids (such as cotton and tobacco), but the evolutionary analysis of them during polyploidization is rare. With the completion of genome sequencing, allotetraploid Brassica napus and its diploid progenitors (B. rapa and B. oleracea) are a good system for studying this question. In this study, 52, 25 and 29 WOX genes were identified in allotetraploid B. napus (2n = 4x = 38, AnCn), the An genome donor B. rapa (2n = 2x = 20, Ar) and the Cn genome donor B. oleracea (2n = 2x = 18, Co), respectively. All identified WOX genes in B. napus and its diploid progenitors were divided into three clades, and these genes were selected to perform gene structure and chromosome location analysis. The results showed that at least 70 and 67% of WOX genes maintained the same gene structure and relative position on chromosomes, respectively, indicating that WOX genes in B. napus were highly conserved at the DNA level during polyploidization. In addition, the analysis of duplicated genes and transposable elements (TEs) near WOX genes showed that whole-genome triplication (WGT) events, segmental duplication and abundant TEs played important roles in the expansion of the WOX gene family in B. napus. Moreover, the analysis of the expression profiles of WOX gene pairs with evolutionary relationships suggested that the WOX gene family may have changed at the transcriptional regulation level during polyploidization. The results of this study increased our understanding of the WOX genes in B. napus and its diploid progenitors, providing a rich resource for further study of WOX genes in these species. In addition, the changes in WOX genes during the process of polyploidization were discussed from the aspects of gene number, gene structure, gene relative location and gene expression, which provides a reference for future polyploidization analysis.

An elucidation of how the selection pressures caused by habitat environments affect plant plastid genomes and lead to the adaptive evolution of plants, is a very intense area of research in evolutionary biology. The genus Paphiopedilum is a predominant group of orchids that includes over 66 species with high horticultural and ornamental value. However, owing to the destructive exploitation and habitat deterioration of wild germplasm resources of Paphiopedilum, it needs more molecular genetic resources and studies on this genus. The chloroplast is cytoplasmically inherited and often used in evolutionary studies. Thus, for this study, we newly sequenced, assembled and annotated five chloroplast genomes of the Paphiopedilum species. The size of these genomes ranged from 155,886 bp (P. henryanum) to 160,503 bp (P. ‘GZSLKY’ Youyou) and they contained 121–122 genes, which consisted of 76 protein coding genes, eight ribosomal RNAs, and 37–38 transfer RNAs. Combined with the other 14 Paphiopedilum species, the characteristics of the repeat sequences, divergent hotspot regions, and the condo usage bias were evaluated and identified, respectively. The gene transfer analysis showed that some fragments of the ndh and ycf gene families were shared by both the chloroplast and nucleus. Although the genomic structure and gene content was conserved, there was a significant boundary shift caused by the inverted repeat (IR) expansion and small single copy (SSC) contraction. The lower GC content and loss of ndh genes could be the result of adaptive evolutionary responses to its unique habitats. The genes under positive selection, including accD, matK, psbM, rpl20, rps12, ycf1, and ycf2 might be regarded as potential candidate genes for further study, which significantly contribute to the adaptive evolution of Paphiopedilum.

Wall-associated kinase (WAK) and WAK-like kinase (WAKL) are receptor-like kinases (RLKs), which play important roles in signal transduction between the cell wall and the cytoplasm in plants. WAK/WAKLs have been studied in many plants, but were rarely studied in the important economic walnut tree. In this study, 27 and 14 WAK/WAKL genes were identified in Juglans regia and its wild related species Juglans mandshurica, respectively. We found tandem duplication might play a critical role in the expansion of WAK/WAKL gene family in J. regia, and most of the WAK/WAKL homologous pairs underwent purified selection during evolution. All WAK/WAKL proteins have the extracellular WAK domain and the cytoplasmic protein kinase domain, and the latter was more conserved than the former. Cis-acting elements analysis showed that WAK/WAKL might be involved in plant growth and development, plant response to abiotic stress and hormones. Gene expression pattern analysis further indicated that most WAK/WAKL genes in J. regia might play a role in the development of leaves and be involved in plant response to biotic stress. Our study provides a new perspective for the evolutionary analysis of gene families in tree species and also provides potential candidate genes for studying WAK/WAKL gene function in walnuts.

Polyploidization is a common event in the evolutionary history of angiosperms, and there will be some changes in the genomes of plants other than a simple genomic doubling after polyploidization. Allotetraploid Brassica napus and its diploid progenitors (B. rapa and B. oleracea) are a good group for studying the problems associated with polyploidization. On the other hand, the EIN3/EIL gene family is an important gene family in plants, all members of which are key genes in the ethylene signaling pathway. Until now, the EIN3/EIL gene family in B. napus and its diploid progenitors have been largely unknown, so it is necessary to comprehensively identify and analyze this gene family. In this study, 13, 7 and 7 EIN3/EIL genes were identified in B. napus (2n = 4x = 38, AnCn), B. rapa (2n = 2x = 20, Ar) and B. oleracea (2n = 2x = 18, Co). All of the identified EIN3/EIL proteins were divided into 3 clades and further divided into 8 sub-clades. Ka/Ks analysis showed that all identified EIN3/EIL genes underwent purifying selection after the duplication events. Moreover, gene structure analysis showed that some EIN3/EIL genes in B. napus acquired introns during polyploidization, and homolog expression bias analysis showed that B. napus was biased towards its diploid progenitor B. rapa. The promoters of the EIN3/EIL genes in B. napus contained more cis-acting elements, which were mainly involved in endosperm gene expression and light responsiveness, than its diploid progenitors. Thus, B. napus might have potential advantages in some biological aspects. The results indicated allotetraploid B. napus might have potential advantages in some biological aspects. Moreover, our results can increase the understanding of the evolution of the EIN3/EIL gene family in B. napus, and provided more reference for future research about polyploidization.