Search

In order to make reasonable use of collected and preserved Dendrobium germplasm resources, ISSR molecular marker method was used to analyze the genetic relationship and genetic diversity of 22 Dendrobium species. A total of 6 primers with clear amplification bands, high polymorphism and good repeatability were chosen from 100 ISSR primers. The selected primers were used to amplify the genomic DNA of 22 Dendrobium species by PCR, and a total of 241 bands were generated, of which 241 were polymorphic bands. Polymorphic ratio was 100%. By GenAlEx 6.5 software, average value of observed allele number, effective number of alleles, Nei's gene diversity and Shannon's information index was 1.983, 1.167, 0.133 and 0.247, respectively, indicating that a high level of genetic diversity among 22 Dendrobium species. The genetic similarity coefficient among 22 Dendrobium species ranged from 0.698 4 to 0.878 7 by NTSYS-pc 2.1 software. UPGMA clustering based on genetic similarity coefficient, 22 Dendrobium species could be divided into 10 groups when genetic similarity was 0.795. UPGMA clustering results are consistent with traditional morphological classification results. The DNA fingerprint map constructed with 3 pairs of primers can separately identify 22 Dendrobium species. This research laid a theoretical foundation for the identification of Dendrobium germplasm resources and the selection of parents for cross breeding.

Dendrobium nestor is a famous orchid species in the Orchidaceae family. There is a diversity of flower colorations in the Dendrobium species, but knowledge of the genes involved and molecular mechanism underlying the flower color formation in D. nestor is less studied. Therefore, we performed transcriptome profiling using Illumina sequencing to facilitate thorough studies of the purple color formation in petal samples collected at three developmental stages, namely—flower bud stage (F), half bloom stage (H), and full bloom stage (B) in D. nestor. In addition, we identified key genes and their biosynthetic pathways as well as the transcription factors (TFs) associated with purple flower color formation. We found that the phenylpropanoid–flavonoid–anthocyanin biosynthesis genes such as phenylalanine ammonia lyase, chalcone synthase, anthocyanidin synthase, and UDP-flavonoid glucosyl transferase, were largely up-regulated in the H and B samples as compared to the F samples. This upregulation might partly account for the accumulation of anthocyanins, which confer the purple coloration in these samples. We further identified several differentially expressed genes related to phytohormones such as auxin, ethylene, cytokinins, salicylic acid, brassinosteroid, and abscisic acid, as well as TFs such as MYB and bHLH, which might play important roles in color formation in D. nestor flower. Sturdy upregulation of anthocyanin biosynthetic structural genes might be a potential regulatory mechanism in purple color formation in D. nestor flowers. Several TFs were predicted to regulate the anthocyanin genes through a K-mean clustering analysis. Our study provides valuable resource for future studies to expand our understanding of flower color development mechanisms in D. nestor.

Habenaria rhodocheila is different from other species in the genus as it has bright yellow-orange, orange-red or red floral colors and grows in subtropical evergreen broad-leaved forests. It is listed as a level II protected plant in China. This study focused on details of the pollination mechanism, including floral structure, the pollinator and its behavior, the pollination process, and fruit set in its natural environment compared to controlled artificial pollination. Our results showed that the flowers of H. rhodocheila are self-compatible, but rely on a pollinating agent due to the lack of an automatic self-pollination mechanism. At three sites the flowers of H. rhodocheila were frequently pollinated by a species of the swallowtail butterfly Papilio helenus L. During pollination, the butterfly inserts its proboscis into the spur aperture. The base of the proboscis then contacts the viscidia and the pollinarium sticks to the insect, followed by contact between pollinia and stigmas. The length of the proboscis of P. helenus is comparable to, but slightly shorter than the length of the floral spur. The pollination activity generally occurs between 9:30 AM to 1:30 PM daily and is especially frequent between 10:30 AM and 11:30 AM. These results suggest that the similarity between the length of the butterfly's proboscis and the length of the orchid's spur is a major factor contributing to the efficient pollination of H. rhodocheila in its natural habitat. Most species in Habenaria are moth-pollinated, whereas our research has shown that H. rhodocheila in subtropical evergreen broad-leaved forests in China is specifically adapted to butterfly pollination by P. helenus.