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Younkin GC, Alani ML, Capador AP, Fischer HD, Mirzaei M, Hastings AP, Agrawal AA, Jander G. Cardiac glycosides protect wormseed wallflower (Erysimum cheiranthoides) against some, but not all, glucosinolate-adapted herbivores. THE NEW PHYTOLOGIST 2024; 242:2719-2733. [PMID: 38229566 PMCID: PMC11116068 DOI: 10.1111/nph.19534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Accepted: 12/22/2023] [Indexed: 01/18/2024]
Abstract
The chemical arms race between plants and insects is foundational to the generation and maintenance of biological diversity. We asked how the evolution of a novel defensive compound in an already well-defended plant lineage impacts interactions with diverse herbivores. Erysimum cheiranthoides (Brassicaceae), which produces both ancestral glucosinolates and novel cardiac glycosides, served as a model. We analyzed gene expression to identify cardiac glycoside biosynthetic enzymes in E. cheiranthoides and characterized these enzymes via heterologous expression and CRISPR/Cas9 knockout. Using E. cheiranthoides cardiac glycoside-deficient lines, we conducted insect experiments in both the laboratory and field. EcCYP87A126 initiates cardiac glycoside biosynthesis via sterol side-chain cleavage, and EcCYP716A418 has a role in cardiac glycoside hydroxylation. In EcCYP87A126 knockout lines, cardiac glycoside production was eliminated. Laboratory experiments with these lines revealed that cardiac glycosides were highly effective defenses against two species of glucosinolate-tolerant specialist herbivores, but did not protect against all crucifer-feeding specialist herbivores in the field. Cardiac glycosides had lesser to no effect on two broad generalist herbivores. These results begin elucidation of the E. cheiranthoides cardiac glycoside biosynthetic pathway and demonstrate in vivo that cardiac glycoside production allows Erysimum to escape from some, but not all, specialist herbivores.
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Affiliation(s)
- Gordon C. Younkin
- Boyce Thompson Institute, 533 Tower Rd, Ithaca, NY 14853, USA
- Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853
| | - Martin L. Alani
- Boyce Thompson Institute, 533 Tower Rd, Ithaca, NY 14853, USA
| | | | | | - Mahdieh Mirzaei
- Boyce Thompson Institute, 533 Tower Rd, Ithaca, NY 14853, USA
| | - Amy P. Hastings
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
| | - Anurag A. Agrawal
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
| | - Georg Jander
- Boyce Thompson Institute, 533 Tower Rd, Ithaca, NY 14853, USA
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Younkin GC, Alani ML, Capador AP, Fischer HD, Mirzaei M, Hastings AP, Agrawal AA, Jander G. Cardiac glycosides protect wormseed wallflower ( Erysimum cheiranthoides) against some, but not all, glucosinolate-adapted herbivores. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.19.558517. [PMID: 37790475 PMCID: PMC10542140 DOI: 10.1101/2023.09.19.558517] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/05/2023]
Abstract
The chemical arms race between plants and insects is foundational to the generation and maintenance of biological diversity. We asked how the evolution of a novel defensive compound in an already well-defended plant lineage impacts interactions with diverse herbivores. Erysimum cheiranthoides (Brassicaceae), which produces both ancestral glucosinolates and novel cardiac glycosides, served as a model.We analyzed gene expression to identify cardiac glycoside biosynthetic enzymes in E. cheiranthoides and characterized these enzymes via heterologous expression and CRISPR/Cas9 knockout. Using E. cheiranthoides cardiac glycoside-deficient lines, we conducted insect experiments in both the laboratory and field.EcCYP87A126 initiates cardiac glycoside biosynthesis via sterol side chain cleavage, and EcCYP716A418 has a role in cardiac glycoside hydroxylation. In EcCYP87A126 knockout lines, cardiac glycoside production was eliminated. Laboratory experiments with these lines revealed that cardiac glycosides were highly effective defenses against two species of glucosinolate-tolerant specialist herbivores but did not protect against all crucifer-feeding specialist herbivores in the field. Cardiac glycosides had lesser to no effect on two broad generalist herbivores.These results begin elucidation of the E. cheiranthoides cardiac glycoside biosynthetic pathway and demonstrate in vivo that cardiac glycoside production allows Erysimum to escape from some, but not all, specialist herbivores.
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Affiliation(s)
- Gordon C. Younkin
- Boyce Thompson Institute, 533 Tower Rd, Ithaca, NY 14853, USA
- Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853
| | - Martin L. Alani
- Boyce Thompson Institute, 533 Tower Rd, Ithaca, NY 14853, USA
| | | | | | - Mahdieh Mirzaei
- Boyce Thompson Institute, 533 Tower Rd, Ithaca, NY 14853, USA
| | - Amy P. Hastings
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
| | - Anurag A. Agrawal
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
| | - Georg Jander
- Boyce Thompson Institute, 533 Tower Rd, Ithaca, NY 14853, USA
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Quantification of plant cardenolides by HPLC, measurement of Na +/K +-ATPase inhibition activity, and characterization of target enzymes. Methods Enzymol 2023; 680:275-302. [PMID: 36710014 DOI: 10.1016/bs.mie.2022.08.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The biosynthesis of cardiac glycosides, broadly classified as cardenolides and bufadienolides, has evolved repeatedly among flowering plants. Individual species can produce dozens or even hundreds of structurally distinct cardiac glycosides. Although all cardiac glycosides exhibit biological activity by inhibiting the function of the essential Na+/K+-ATPase in animal cells, they differ in their level of inhibitory activity. For within- and between-species comparisons of cardiac glycosides to address ecological and evolutionary questions, it is necessary to not only quantify their relative abundance, but also their effectiveness in inhibiting the activity of different animal Na+/K+-ATPases. Here we describe protocols for characterizing the amount and toxicity of cardenolides from plant samples and the degree of insect Na+/K+-ATPase tolerance to inhibition: (1) an HPLC-based assay to quantify the abundance of individual cardenolides in plant extracts, (2) an assay to quantify inhibition of Na+/K+-ATPase activity by plant extracts, and (3) extraction of insect Na+/K+-ATPases for inhibition assays.
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