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Abstract Detail


Smith, Chelsea R. [1], Teisher, Jordan [2], Straub, Shannon [3], Livshultz, Tatyana [4].

Does herbivore co-option of a plant defense drive its loss?: Testing the defense de-escalation of pyrrolizidine alkaloid evolution in Apocynaceae (the dogbane and milkweed family).

Pyrrolizidine alkaloids (PAs) are secondary metabolites that have evolved independently in 12 flowering plant families, including Apocynaceae (the dogbane and milkweed family). Multiple insect lineages have co-opted PAs for defense, including Lepidoptera subfamily Danainae (the milkweed and clearwing butterflies). We have previously shown that the first gene of the PA biosynthetic pathway, homospermidine synthase (hss), evolved from deoxyhupusine synthase (dhs) early in the diversification of one lineage of Apocynaceae (the APSA clade), and that 92% of Apocynaceae larval host plant records for Danainae belong to this clade. We reconstructed the ancestral hss-like gene as having a functionally characterized HSS-specific amino acid motif (V/D at positions 305/308), indicating ancestral presence of PA biosynthesis followed by at least four losses of the amino acid motif and one pseudogenization event (Livshultz et al., 2018). Now we increase sampling of hss- and dhs-like genes of APSA clade species from 39 to 97 species, representing 13 of 15 major lineages classified as tribes or subfamilies.  All APSA clade species except Wrightieae have both an hss- and a dhs-like gene, localizing the hss/dhs duplication to the common ancestor of all PA-producing Apocynaceae. All dhs-like loci had the typical DHS amino acid motif (I/N), as did the hss-like loci of Asclepiadeae and most Marsdenieae species. The hss-like loci in the remaining species had either the HSS-specific amino acid motif (V/D) or an intermediate motif (I/D) with unknown function. A total of 9 pseudogenes were found in three lineages (Apocyneae, Nerieae, Asclepiadeae), including both a pseudogene and an intact hss-like gene in Calotropis gigantea. The presence of pseudogenes and DHS-like I/N amino acid motifs in translated hss-like loci across the APSA clade potentially indicates that the ability to produce PAs has been lost several times. However, whether PA biosynthesis evolved once or multiple times independently within Apocynaceae depends on the currently unknown function of HSS-like enzymes with the I/D motif.

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Related Links:
Previous work: "Evolution of pyrrolizidine alkaloid biosynthesis in Apocynaceae: revisiting the defence de-escalation hypothesis"

1 - Drexel University, Department of Biodiversity, Earth, and Environmental Sciences, 3141 Chestnut Stree, Philadelphia, PA, 19104, USA
2 - The Academy Of Natural Sciences Of Drexel University, Botany, 1900 Benjamin Franklin Parkway, Philadelphia, PA, 19103, United States
3 - Hobart and William Smith Colleges, Department of Biology, 300 Pulteney St., Geneva, NY, 14456, USA
4 - Drexel University, Biodiversity Earth and Environmental Sciences, Academy Of Natural Sciences Of Drexel University, 1900 Benjamin Franklin Parkway, Philadelphia, PA, 19103, United States

secondary chemistry
biochemical evolution
plant-insect interactions
target enrichment.

Presentation Type: Poster
Session: P, Macroevolution
Location: Grand Ballroom - Exhibit Hall/Mayo Civic Center
Date: Monday, July 23rd, 2018
Time: 5:30 PM This poster will be presented at 6:15 pm. The Poster Session runs from 5:30 pm to 7:00 pm. Posters with odd poster numbers are presented at 5:30 pm, and posters with even poster numbers are presented at 6:15 pm.
Number: PME002
Abstract ID:661
Candidate for Awards:None

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