Differences and biocontrol potential of haustorial endophytic fungi from Taxillus Chinensis on different host plants

BACKGROUND

To explore the community composition and diversity of the endophytic fungi in Taxillus chinensis, samples of the parasites growing on seven different hosts, Morus alba, Prunus salicina, Phellodendron chinense, Bauhinia purpurea, Dalbergia odorifera, Diospyros kaki and Dimocarpus longan, were isolated. The strains were identified by their morphological characteristics and their internal transcribed spacer (ITS) sequences.

RESULTS

150 different endophytic fungi were isolated from the haustorial roots of the seven hosts with a total isolation rate of 61.24%. These endophytic fungi were found to belong to 1 phylum, 2 classes, 7 orders, 9 families, 11 genera and 8 species. Among of them, Pestalotiopsis, Neopestalotiopsis and Diaporthe were the dominant genera, accounting for 26.67, 17.33 and 31.33% of the total number of strains, respectively. Diversity and similarity analyses showed that the endophytic fungi isolated from D. longan (H'=1.60) had the highest diversity index. The highest richness indexes were found in M. alba and D. odorifera (both 2.23). The evenness index of D. longan was the highest (0.82). The similarity coefficient of D. odorifera was the most similar to D. longan and M. alba (33.33%), while the similarity coefficient of P. chinense was the lowest (7.69%) with M. alba and D. odorifera. Nine strains showed antimicrobial activities. Among them, Pestalotiopsis sp., N. parvum and H. investiens showed significant antifungal activity against three fungal phytopathogens of medicinal plants. At the same time, the crude extracts from the metabolites of the three endophytic fungi had strong inhibitory effects on the three pathogens. Pestalotiopsis sp., N. parvum and H. investiens had the strongest inhibitory effects of S. cucurbitacearum, with inhibitory rates of 100%, 100% and 81.51%, respectively. In addition, N. parvum had a strong inhibitory effect on D. glomerata and C. cassicola, with inhibitory rates of 82.35% and 72.80%, respectively.

CONCLUSIONS

These results indicate that the species composition and diversity of endophytic fungi in the branches of T. chinensis were varied in the different hosts and showed good antimicrobial potential in the control of plant pathogens.

First Report of Phytoplasma Belongs to 16SrV Group Associated with Witches'-broom Disease of Taxillus chinensis in China

Taxillus chinensis (DC.) Danser is a hemiparasitic shrub, widespread in Southern China (Fu et al., 2001). T. chinensis can parasitize a wide range of species (e.g., Camellia spp., Ficus virens and Osmanthus fragrans), which obviously suppressed host growth by robbing nutrient and water through haustorium, causing considerable tree damage. During field visits to Dongguan (22°86'N, 13°97'E) and Guangzhou (23°19'N, 113°31'E), Guangdong Province, in April-July 2021, the typical phytoplasma-suspected symptom manifested as stunting, leaflet, leaf chlorosis and witches'-broom were observed in almost 36% of T. chinensis plants. Leaf samples were collected from six randomly collected plants with symptoms and six symptomless plants (Fig 1). Among them, half of T. chinensis plants parasitized on the host Elaeocarpus sylvestris, the other half on the O. fragrans. No apparent symptoms were observed on both two host plants. Total DNA was extracted from 0.5 g fresh leaf of T. chinensis plants with and without symptoms, as well as two host plants E. sylvestris and O. fragrans, using the CTAB method (Doyle et al., 1990). Nested polymerase chain reactions (PCRs) were performed on DNA extracts of all tested plants with primer pairs of P1/P7 and R16mF2/R16mR1 for 16S rRNA gene (Lee et al., 1993) and rp(v)F1/rpR1 for rp gene (Lee et al., 1998). All amplicons were obtained from symptomatic samples of T. chinensis and host plant E. sylvestris, whereas no such products resulted from DNAs of symptomless plants and O. fragrans. The amplicons were purified and sequenced by Sanger method (Rui Biotech, Guangzhou, China). The amplicon of 16S rRNA and rp genes is 1346 bp and 938 bp, respectively. BLAST comparison of the 16S rRNA (accession no. OL412744) and rp (accession no. OL473789) sequences of the T. chinensis witches'-broom phytoplasma yielded 99.6% sequence identity with those of phytoplasmas of group 16SrV jujube witches'-broom (JWB) phytoplasma (accession no. CP025121 for 16S rRNA gene and AF396941 for rp gene). The 16S rRNA gene sequence of phytoplasma in host plant E. sylvestris (accession no. OM885990) is 99.7% similarity to the 'Elaeocarpus zollingeri' yellows phytoplasma (accession no. LC257960) and 99.4% similarity to the 'Elaeocarpus sylvestris' decline phytoplasma (accession no. MW553140), but 95.8% similarity to the 16S rRNA gene of phytoplasma in T. chinensis. The virtual RFLP tool, iPhyClassifier delineated the T. chinensis phytoplasma (accession no. OL412744) to group 16SrV-B (accession no. AB052876) with the similarity coefficient 1.0 (Fig 2), and phytoplasma in E. sylvestris to group 16Sr group XXXII with the similarity coefficient 0.97. Phylogeny analyses of 16S rRNA and rp genes (MEGA version 7.0.14, USA) using reference phytoplasmas from GenBank confirmed sequencing results and placed the T. chinensis phytoplasma in group 16SrV-B (Fig. 3 and 4). In China, the 16SrV-B phytoplasma group has been reported in Amaranthus retroflexus (Yang et al., 2011), Liriodendron chinense (Li et al., 2012), Prunus salicina (Gao et al., 2020) and sweet potato (Li et al., 2021). This is the first report of a 'Ca. Phytoplasma ziziphi', 16SrV-B related phytoplasma associated with parasitic T. chinensis in China. The results of this study indicate that T. chinensis could be a vector to spread phytoplasmas 16SrV group through parasitism and this can be helpful for related research.

Metabolomics Study of Flavonoids of Taxilluschinensis on Different Hosts Using UPLC-ESI-MS/MS

The goal of this study was to identify and compare the main biomarkers of Taxillus chinensis from different hosts. A metabolomics approach utilizing ultra-pressure liquid chromatography coupled with tandem mass spectrometry (UPLC-MS), including cluster analysis, sample correlation analysis and orthogonal partial least squares discriminant analysis, was used to explore the flavonoid metabolites of Taxillus chinensis growing on different hosts. Results: The total flavonoids content (up to 30.08 mg/g) in Taxillus chinensis from Morus alba (CSG) was significantly higher than that from growth on Liquidambar formosana (CFG) or Clausena lansium (CHG) (p < 0.01). There were 23 different metabolites between CSG and CHG, 23 different metabolites between CSG and CFG, and 19 different metabolites between CHG and CFG.&nbsp;The results demonstrated that different hosts exerted a large influence on the metabolites of Taxillus chinensis; it was found that CSG differed from CFG and CHG in eleven metabolic compounds, ten of which were upregulated and one of which was downregulated. Most of these metabolites derive from compounds contained in the host plant, white mulberry (Morus alba); many feature potent anti-cancer effects. Differences in host can influence the type and abundance of flavonoids in parasitic plants such as Taxillus chinensis, which is of great significance to researchers seeking to understand the formation mechanism of Taxillus chinensis metabolites. Therefore, attention should be paid to the species of host plant when studying the Taxillus chinensis metabolome. Plants grown on Morus alba offer the greatest potential for the development of new anti-cancer drugs.

Complete chloroplast genome sequence of Taxillus chinensis (Loranthaceae): a hemiparasitic shrub in South China

Taxillus chinensis (DC) Danser, which is a hemiparasitic shrub distributed in southern China and Southeast Asian countries, is wildly used in various traditional Chinese medicine prescriptions. In this study, the complete chloroplast genome of the T. chinensis was assembled from the whole genome Illumina sequencing data. The complete plastome is a typical quadripartite structure with a length of 121,305 bp, which contained two inverted repeats (IRs) of 22,460 bp separated by a large single-copy (LSC) and a small single copy (SSC) of 70,295 bp and 6090 bp, respectively. The plastome contains 106 genes, comprising 66 protein-coding genes, 28 tRNA genes, eight rRNA genes, and four processed pseudogenes. The overall GC content of the plastome is 37.4%, which is unevenly distributed across the whole chloroplast genome. The phylogenetic analysis shows that T. chinensis was closely related to the congeneric species T. sutchuenensis.

[Correlation study on chemical constitutes of cardiac glycosides in Taxillus chinensis and its Nerium indicum host by UPLC-Q-TOF-MS/MS]

To build up an identification method on cardiac glycosides in Taxillus chinensis and its Nerium indicum host, and evaluate the influence on medicine quality from host to T. chinensis, ultra-performance liquid chromatography coupled with quadrupole-time-of-flight tandem mass-mass spectrometry(UPLC-Q-TOF-MS/MS)was applied. The samples of T. chinensis(harvested from N. indicum)and its N. indicum host were collected in field. The samples of T. chinensis(harvested from Morus alba)and its M. alba host was taken as control substance. All samples were extracted by ultrasonic extraction in 70% ethanol. Chromatographic separation was performed on an ACQUITY UPLC HSS T3 C_(18)(2.1 mm×100 mm,1.8 μm)column at 40 ℃. Gradient elution was applied, and the mobile phase was consisted of 0.1% formic acid water and acetonitrile. The 0.5 μL of sample solution was injected and the flow rate of the mobile phase was kept at 0.6 mL·min~(-1) in each run. It was done to identify cardiac glycosides and explore the chemical composition correlation in T. chinensis and its N. indicum host by analyzing positive and negative ion mode mass spectrometry data, elemental composition, cardiac glycoside reference substance and searching related literatures. A total of 29 cardiac glycosides were identified, 28 of it belonged to N. indicum host, 5 belonged to T. chinensis(harvested from N. indicum host), none of cardiac glycoside was identified in T. chinensis(harvested from M. alba host). The result could provide a reference in evaluating the influence in T. chinensis medicine quality from host. It was rapid, accurate, and comprehensive to identify cardiac glycosides in T. chinensis and its N. indicum host by UPLC-Q-TOF-MS/MS.

Identification and analysis of cardiac glycosides in Loranthaceae parasites Taxillus chinensis (DC.) Danser and Scurrula parasitica Linn. and their host Nerium indicum Mill

To evaluate the effect of the host plant on the quality of Loranthaceae species as medicinal raw material, ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS) was used to identify cardiac glycosides in Nerium indicum and its parasitic plant species Taxillus chinensis and Scurrula parasitica. Samples were collected from N. indicum and these parasites, while Morus alba and its parasite T. chinensis and Osmanthus fragrans and its parasite S. parasitica were used as controls. Based on mass spectrometry data and elemental composition analysis of positive and negative ion modes, in combination with standard cardiac glycosides and relevant literature, cardiac glycosides in N. indicum and its parasites T. chinensis and S. parasitica were identified, and their correlations were analyzed. A total of 29 cardiac glycosides were identified, among which 28 were found in N. indicum parasitized by T. chinensis; 25 cardiac glycosides were identified in the same host under attack by S. parasitica; five cardiac glycosides were identified in both T. chinensis and S. parasitica, which grew parasitically on N. indicum, whereas no cardiac glycosides were identified in M. alba parasitized by T. chinensis, or in O. fragrans parasitized by S. parasitica. We conclude that UPLC-Q-TOF-MS/MS technology can identify cardiac glycosides in N. indicum and parasites T. chinensis and S. parasitica rapidly, accurately, and thoroughly. N. indicum will transfer its own cardiac glycosides to its parasites through the special host-parasite interaction. Our results provide a reference basis for evaluating the influence of the host plant on the quality of medicinal compounds obtained from Loranthaceae species.