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- Title
Evolution of pyrrolizidine alkaloid biosynthesis in Apocynaceae: revisiting the defence de‐escalation hypothesis.
- Authors
Livshultz, Tatyana; Kaltenegger, Elisabeth; Straub, Shannon C. K.; Weitemier, Kevin; Hirsch, Elliot; Koval, Khrystyna; Mema, Lumi; Liston, Aaron
- Abstract
Summary: Plants produce specialized metabolites for their defence. However, specialist herbivores adapt to these compounds and use them for their own benefit. Plants attacked predominantly by specialists may be under selection to reduce or eliminate production of co‐opted chemicals: the defence de‐escalation hypothesis. We studied the evolution of pyrrolizidine alkaloids (PAs) in Apocynaceae, larval host plants for PA‐adapted butterflies (Danainae, milkweed and clearwing butterflies), to test if the evolutionary pattern is consistent with de‐escalation. We used the first PA biosynthesis specific enzyme (homospermidine synthase, HSS) as tool for reconstructing PA evolution. We found <italic>hss</italic> orthologues in diverse Apocynaceae species, not all of them known to produce PAs. The phylogenetic analysis showed a monophyletic origin of the putative <italic>hss</italic> sequences early in the evolution of one Apocynaceae lineage (the APSA clade). We found an <italic>hss</italic> pseudogene in <italic>Asclepias syriaca</italic>, a species known to produce cardiac glycosides but no PAs, and four losses of an HSS amino acid motif. APSA clade species are significantly more likely to be Danainae larval host plants than expected if all Apocynaceae species were equally likely to be exploited. Our findings are consistent with PA de‐escalation as an adaptive response to specialist attack.
- Subjects
PLANT defenses; PLANT metabolites; HERBIVORES; PYRROLIZIDINES; APOCYNACEAE; HOST plants; BIOSYNTHESIS
- Publication
New Phytologist, 2018, Vol 218, Issue 2, p762
- ISSN
0028-646X
- Publication type
Article
- DOI
10.1111/nph.15061