Pyrrolizidine alkaloids are synthesized and accumulated in flower of Myosotis scorpioides

Kyohei Takano; Hajime Ikeda; Kojiro Takanashi

doi:10.1007/s10265-024-01525-4

Pyrrolizidine alkaloids are synthesized and accumulated in flower of Myosotis scorpioides

J Plant Res. 2024 Feb 18. doi: 10.1007/s10265-024-01525-4. Online ahead of print.

Authors

Kyohei Takano¹, Hajime Ikeda^{2

3}, Kojiro Takanashi^{4

5}

Affiliations

¹ Department of Science, Graduate School of Science and Technology, Shinshu University, Asahi 3-1-1, Matsumoto, Nagano, 390-8621, Japan.
² Institute of Plant Science and Resources, Okayama University, 2-20-1 Chuo, Kurashiki, Okayama, 710-0046, Japan.
³ Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba Meguro-Ku, Tokyo, 153-8902, Japan.
⁴ Department of Science, Graduate School of Science and Technology, Shinshu University, Asahi 3-1-1, Matsumoto, Nagano, 390-8621, Japan. takanashi@shinshu-u.ac.jp.
⁵ Department of Biology, Faculty of Science, Shinshu University, Asahi 3-1-1, Matsumoto, Nagano, 390-8621, Japan. takanashi@shinshu-u.ac.jp.

PMID: 38368590
DOI: 10.1007/s10265-024-01525-4

Abstract

Pyrrolizidine alkaloids (PAs) are specialized metabolites that are produced by various plant families that act as defense compounds against herbivores. On the other hand, certain lepidopteran insects uptake and utilize these PAs as defense compounds against their predators and as precursors of their sex pheromones. Adult males of Parantica sita, a danaine butterfly, convert PAs into their sex pheromones. In early summer, P. sita swarms over the flowers of Myosotis scorpioides, which belongs to the family Boraginaceae. M. scorpioides produces PAs, but the organs in which PAs are produced and whether P. sita utilizes PAs in M. scorpioides are largely unknown. In the present study, we clarified that M. scorpioides accumulates retronecine-core PAs in N-oxide form in all organs, including flowers. We also identified two M. scorpioides genes encoding homospermidine synthase (HSS), a key enzyme in the PA biosynthetic pathway, and clarified that these genes are expressed in all organs where PAs accumulate. Phylogenetic analysis suggested that these two HSS genes were originated from gene duplication of deoxyhypusine synthase gene like other HSS genes in PA-producing plants. These results suggest that PAs are synthesized and accumulated in the flower of M. scorpioides and provide a possibility for a PA-mediated interaction between P. sita and M. scorpioides.

Keywords: Deoxyhypusine synthase; Homospermidine synthase; Myosotis scorpioides; Pyrrolizidine alkaloid.