Quality variation and salt-alkali-tolerance mechanism of Cynomorium songaricum: Interacting from microbiome-transcriptome-metabolome

Addressing soil salinization and implementing sustainable practices for cultivating cash crops on saline-alkali land is a prominent global challenge. Cynomorium songaricum is an important salt-alkali tolerant medicinal plant capable of adapting to saline-alkali environments. In this study, two typical ecotypes of C. songaricum from the desert-steppe (DS) and saline-alkali land (SAL) habitats were selected. Through the integration of multi-omics with machine learning, the rhizosphere microbial communities, genetic maps, and metabolic profiles of two ecotypes were created and the crucial factors for the adaptation of C. songaricum to saline-alkali stress were identified, including 7 keystone OTUs (i.e. Novosphingobium sp., Sinorhizobium meliloti, and Glycomyces sp.), 5 core genes (cell wall-related genes), and 10 most important metabolites (i.e. cucurbitacin D and 3-Hydroxybutyrate) were identified. Our results indicated that under saline-alkali environments, the microbial competition might become more intense, and the microbial community network had the simple but stable structure, accompanied by the changes in the gene expression related to cell wall for adaptation. However, this regulation led to the reduction in active ingredients, such as the accumulation of flavonoids and organic acid, and enhanced the synthesis of bitter substances (cucurbitacin D), resulting in the decrease in the quality of C. songaricum. Therefore, compared to the SAL ecotype, the DS was more suitable for the subsequent development of medicinal and edible products of C. songaricum. Furthermore, to explore the reasons for this quality variation, we constructed a comprehensive microbial-genetic-metabolic regulatory network, revealing that the metabolism of C. songaricum was primarily influenced by genetic factors. These findings not only offer new insights for future research into plant salt-alkali tolerance strategies but also provide a crucial understanding for cultivating high-quality medicinal plants.

Scent chemistry and pollinators in the holoparasitic plant Cynomorium songaricum (Cynomoriaceae)

Holoparasitic plants are interesting heterotrophic angiosperms. However, carrion- or faeces-mimicking is rarely described for such plants. There is no information on the pollination biology of Cynomoriaceae, despite the fact that these plants are rare and vulnerable. This is the first study to reveal pollination in a member of this family, Cynomorium songaricum, a root holoparasite with a distinctive and putrid floral odour. From 2016 to 2018, we studied the floral volatiles, floral visitors and pollinators, behavioural responses of visitors to floral volatiles, breeding system, flowering phenology and floral biology of two wild populations of C. songaricum in Alxa, Inner Mongolia, China. A total of 42 volatiles were identified in inflorescences of C. songaricum. Among these volatiles are compounds known as typical carrion scents, such as p-cresol, indole, dimethyl disulphide and 1-octen-3-ol. C. songaricum is pollinated by various Diptera, such as Musca domestica, M. stabulans (Muscidae), Delia setigera, D. platura (Anthomyiidae), Lucilia sericata, L. caesar (Calliphoridae), Wohlfahrtia indigens, Sarcophaga noverca, S. crassipalpis and Sarcophila meridionalis (Sarcophagidae). The inflorescence scent of C. songaricum attracted these pollinators. The plants significantly benefit from insect pollination, although wind can be a pollen vector in the absence of pollinators. C. songaricum is a cross-pollinated, self-incompatible plant. Our findings suggest that C. songaricum releases malodorous volatiles to attract Diptera to achieve pollination. This new example lays the foundation for further comparative studies in other members of this plant group and contributes to a better understanding of fly-pollinated, carrion mimicking plants.

[Differences of Cynomorium songaricum seed quality and mutual parasitism in different host plants]

In natural conditions, fully ripe Cynomorium songaricum seeds parasitize in Nitraria tangutorum or N. sphaerocarpa or N. sibirica or Zygophyllum xanthoxylom and Peganum harmala, were used in this study to research the morphological characteristics, embryo rate, seed viability, 1 000-grain weight, purity, water content and the seeds of different host parasitic relationship with each other. The results showed that the morphology, color and surface characteristics of the C. songaricum seeds are very similar in different hosts. According to the seed morphology can not be judged on its host. For the host to N. tangutorum or Peganum harmala or N. sibirica, we should choose the round hole screen less than 0.923 1 mm and larger than 1.066 2 mm to cleaning seeds. For the C. songaricum seeds parasitic in N. sphaerocarpa, the choice of slightly less than 0.926 1 mm and larger than 0.985 3 mm round hole screen to cleaning. For the parasitic seeds in Z. xanthoxylom, less than 0.751 3 mm and slightly larger than 1.035 3 mm round hole screen could be used. Highy significant correlation was found among the morphological indexes in C. songaricum seeds (P < 0.01). Morphological indexes and 1 000-grain weight were significantly correlated (0.01 < P < 0.05), but with the seed viability and the embryo rate were not found significant correlation. Grain weight is not related with the seed viability and the Fully mature C. songaricum seed viability is high and water content is low. The difference of the habitats and the host plants should be considered in the seed quality assessment and classification. The C. songaricum seeds on host plants are not selective, and the C. songaricum seeds from the host plants could be parasitized in other host plants.

Stable carbon and nitrogen isotope signatures of root-holoparasitic Cynomorium songaricum and its hosts at the Tibetan plateau and the surrounding Gobi desert in China

We first measured the δ(13)C and δ(15)N values of root holoparasite Cynomorium songaricum and its hosts from 19 sites across four provinces in northwest China, in an attempt to investigate their nutritional relationship at the Tibetan plateau and the surrounding Gobi desert. Our study showed that the δ(13)C of C. songaricum closely mirrored the values of its hosts, Nitraria tangutorum and N. sibirica across all sampling sites. C. songaricum was significantly depleted in (13)C compared to host plants at the Tibetan plateau, showing an average parasite/host δ(13)C difference of-0.6 ‰. In contrast, (15)N of C. songaricum was significantly enriched by+1.3 ‰ compared to the hosts, implying that these holoparasites had other nitrogen resources. Although no difference in the δ(13)C and δ(15)N values between holoparasites and hosts was detected, the δ(13)C and δ(15)N values of holoparasites were significantly correlated with those of their hosts at the Gobi desert. The δ(13)C versus δ(15)N values were significantly but negatively correlated for the hosts; however, holoparasite/host variation in δ(13)C was not correlated with the variation in δ(15)N. The δ(13)C versus δ(15)N values were negatively correlated in C. songaricum, and this relationship tended to be magnified along the increasing elevations independent of the host plants. C. songaricum at the Tibetan plateau exhibited different δ(13)C and δ(15)N signatures compared with those at the Gobi desert. Furthermore, both δ(13)C and δ(15)N values of C. songaricum and its host plants in salt marshes at the Tibetan plateau were different from those in sand sites at the Tibetan plateau and the Gobi desert. Our results indicate that the isotopic difference depends on the different altitudes and habitats and is host-specific.

[New record for China of host plant of Cynomorium songaricumpeganum multisectum]

OBJECTIVE

To investigate the distribution and host plants of Cynomorium songaricum, and provide a scientific basis for the artificial cultivation of C. songaricum and protect the ecological environment in the sandy area.

METHOD

Specimens of C. songaricum in growing area was collected and accessed according to relevant literature and identified.

RESULT

The results showed that a new host plant of C. songaricum-Peganum multisectum was found.

CONCLUSION

A new host plant of C. songaricum, Peganum multisectum was reported, and it is provide the necessary nutrition for normal growth of C. songaricum.

Discovery of the photosynthetic relatives of the "Maltese mushroom" Cynomorium

Background

Although recent molecular phylogenetic studies have identified the photosynthetic relatives of several enigmatic holoparasitic angiosperms, uncertainty remains for the last parasitic plant order, Balanophorales, often considered to include two families, Balanophoraceae and Cynomoriaceae. The nonphotosynthetic (holoparasitic) flowering plant Cynomorium coccineum has long been known to the Muslim world as "tarthuth" and to Europeans as the "Maltese mushroom"; C. songaricum is known in Chinese medicine as "suo yang." Interest in these plants is increasing and they are being extensively collected from wild populations for use in herbal medicines.

Results

Here we report molecular phylogenetic analyses of nuclear ribosomal DNA and mitochondrial matR sequence data that strongly support the independent origin of Balanophoraceae and Cynomoriaceae. Analyses of single gene and combined gene data sets place Cynomorium in Saxifragales, possibly near Crassulaceae (stonecrop family). Balanophoraceae appear related to Santalales (sandalwood order), a position previously suggested from morphological characters that are often assumed to be convergent.

Conclusion

Our work shows that Cynomorium and Balanophoraceae are not closely related as indicated in all past and present classifications. Thus, morphological features, such as inflorescences bearing numerous highly reduced flowers, are convergent and were attained independently by these two holoparasite lineages. Given the widespread harvest of wild Cynomorium species for herbal medicines, we here raise conservation concerns and suggest that further molecular phylogenetic work is needed to identify its photosynthetic relatives. These relatives, which will be easier to cultivate, should then be examined for phytochemical activity purported to be present in the more sensitive Cynomorium.