Triterpenoid saponins as defense compounds of winter cress against herbivorous insects

Winter cress (Barbarea vulgaris) is a wild plant closely related to oil seed rape, radish, rucola, mustard and the reference plant Arabidopsis thaliana. It is resistant to a range of insect species because it produces triterpenoid saponins¹. Saponins are bioactive triterpenoid glycosides found in a variety of plants². We study natural plant resistance to insects with focus on saponin involvement in the resistance.

 

 

We used unbiased LC-MS ecometabolomic approach based on a segregating population of a cross between resistant and susceptible types of winter cress and identified four triterpenoid saponins as the main anti-insecticidal compounds against flea beetles: oleanolic acid cellobioside, hederagenin cellobioside, gypsogenin cellobioside, and 4-epihederagenin cellobioside¹. We are currently developing a method to measure a wider range of metabolites in the segregating population of winter cress by combining GC-MS, LC-MS, NMR, and multivariate and multi-way statistical methods of analysis.

 

Transcriptomic datasets of the resistant and susceptible winter cress types were used for molecular marker design, as well as they were mined for putative key candidate enzymes for saponin biosynthesis: oxidosqualene synthases, cytochromes P450 and family 1 glycosyltransferases.

 

 

We created a genome map of winter cress based on the molecular markers designed and localized genome regions containing genes for saponin and glucosinolate production, hairiness, and flea beetle resistance ³. Genome regions containing genes for resistance and for saponin biosynthesis co-localized. We are currently studying the genes involved in resistance and saponin biosynthesis located within these regions by mining genome and transcriptome sequencing data of the resistant and susceptible winter cress types.

Selected references

1. Kuzina V, Ekstrøm CT, Andersen SB, Nielsen JK, Olsen CE, Bak S (2009) Identification of Defense Compounds in Barbarea vulgaris against the Herbivore Phyllotreta nemorum by an Ecometabolomic Approach. Plant Physiol 151: 1977-1990.
2. Augustin JM, Kuzina V, Andersen SB, Bak S (2011) Biochemistry of triterpenoid saponins: molecular activities, biosynthesis and evolution. Phytochemistry 72: 435-457.
3.  Kuzina V, Nielsen JK, Augustin JM, Torp AM, Bak S, Andersen SB (2011) Barbarea vulgaris Linkage Map and Quantitative Trait Loci for Saponins, Glucosinolates, Hairiness and Resistance to the Herbivore Phyllotreta nemorum. Phytochemistry 72: 188-198.  

Read more about the project Ecogenomics of interaction between plants, pathogens and insects.