Most studies on the host preference of orchids have focused on the association between orchids and host characteristics, but little is known about the differences of mycorrhizal and endophytic fungal communities in epiphytic orchids growing on different host tree species. We selected Dendrobium sinense, a tropical epiphytic orchid, to determine if fungal endophytes from the roots of D. sinense were preferentially correlated with host tree species. Fifty-six fungal operational taxonomic units (OTUs) from 36 host trees were identified. The results indicated that the species richness and diversity of mycorrhizal and endophytic fungal communities isolated from D. sinense roots were strongly influenced by host tree species. Both species richness and diversity indices showed that D. sinense roots on Syzygium buxifolium harbored the most diverse and abundant endophytic fungi. Species of Tulasnellaceae were dominant on S. buxifolium and Rhododendron moulmainense but infrequent on Cyclobalanopsis disciformis and Podocarpus neriifolius. Our results provide evidence for distinct mycorrhizal and endophytic fungal communities on different host tree species. Further research focusing on fungi-orchid-host preference could be conducted to increase our understanding for the in situ conservation of epiphytic orchids.
Dendrobium catenatum has become a rare and endangered medicinal plant due to habitat loss in China. As one of the most important and largest transcription factors, WRKY plays a critical role in response to abiotic stresses in plants. However, little is known regarding the functions of the WRKY family in D. catenatum. In this study, a total of 62 WRKY genes were identified from the D. catenatum genome. Phylogenetic analysis revealed that DcWRKY proteins could be divided into three groups, a division supported by the conserved motif compositions and intron/exon structures. DcWRKY gene expression and specific responses under drought, heat, cold and salt stresses were analyzed through RNA-seq data and RT-qPCR assay. The results showed that these genes had tissue-specificity and displayed different expression patterns in response to abiotic stresses. The expression levels of DcWRKY22, DcWRKY36 and DcWRKY45 were up-regulated by drought stress. Meanwhile, DcWRKY22 was highly induced by heat in roots, and DcWRKY45 was significantly induced by cold stress in leaves. Furthermore, DcWRKY27 in roots and DcWRKY58 in leaves were extremely induced under salt treatment. Finally, we found that all the five genes may function in ABA- and SA-dependent manners. This study identified candidate WRKY genes with possible roles in abiotic stress and these findings not only contribute to our understanding of WRKY family genes, but also provide valuable information for stress resistance development in D. catenatum.
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