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.

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.

The YABBY gene family is a plant transcription factor that exists in all seed plants. YABBY family members have been studied extensively in various plants and were to play significant roles in plant growth and development. Juglans, especially walnuts, are important economic tree species that are widely distributed worldwide. However, the identification and related research of YABBY in Juglans have not been reported to date. In this study, we identified 19 YABBY genes from two Juglans species, namely, J. regia and J. mandshurica. Ten JrYABBY genes and nine JmYABBY genes were divided into five subfamilies (YAB1/3, YAB2, INO, CRC, and YAB5). Sequence analysis revealed that all encoded YABBY protein sequences had a highly conserved YABBY and C2C2 zinc-finger domains. An analysis of the assumed cis-acting elements revealed that JrYABBY and JmYABBY genes were deeply involved in phytohormone and light responses. Further, gene expression pattern analysis suggested that most walnut YABBY genes were likely involved in peel and flower development and responses to biotic stress. This study not only suppled novel insights into the evolutionary basis of YABBY gene families in Juglans, but also provided clues for the further functional verification and investigation of YABBY genes in other tree species.