Glandular Trichomes of Leucosceptrum canum Harbor Defensive Sesterterpenoids

Abstract

On the defense: Sesterterpenoid 1 and its 11‐dehydroxy derivative, which possess a unique C25 skeleton, have been isolated from the glandular trichomes of Leucosceptrum canum. They have potent antifeedant activities and inhibitory effects against pathogenic fungi, which suggest a role of sesterterpenoids in plant defense.

A Geranylfarnesyl Diphosphate Synthase Provides the Precursor for Sesterterpenoid (C25) Formation in the Glandular Trichomes of the Mint Species Leucosceptrum canum

“…To investigate the relative distribution of sesterterpenoids in GTs compared with various whole organs of L. canum, HPLC analysis was performed on extracts of GTs, whole leaves, young stems, and flowers. In addition to previously reported leucosceptroids A (1, t R = 27.3 min) and B (5, t R = 31.8 min) (Luo et al, 2010), a number of other peaks were also detected ( Figure 1). These were not observed previously, possibly due to sampling having been conducted at a different time of year.…”

“…Our previous study of L. canum identified two sesterterpenoids possessing a unique C 25 skeleton, the leucosceptroids A and B, and found these to be present in glandular trichomes (GTs) on surfaces of the aerial parts of the plant (Luo et al, 2010). This suggested that the biosynthesis of these sesterterpenoids was probably also accomplished in GTs, since terpenoids accumulating in these structures in other plant species have been previously reported to be formed in situ (McCaskill et al, 1992;Wagner et al, 2004;Wang et al, 2008;Xie et al, 2008;Schilmiller et al, 2009).…”

“…Since our previous work had indicated that the sesterterpenoids of L. canum function as defense compounds against insect herbivores and pathogens (Luo et al, 2010(Luo et al, , 2011(Luo et al, , 2013a(Luo et al, , 2013b, we were also interested in investigating whether GFDPS expression and sesterterpenoid accumulation could be induced by the defense hormones methyl jasmonate (MJ) and salicylic acid (SA). The qRT-PCR results show that treatment of the plant with 100 mM MJ or 100 mM SA significantly stimulated the expression of GFDPS in the leaves of L. canum saplings ( Figures 2E and 2F).…”

“…In vascular plants, sesterterpenoids are a characteristic feature of the genus Salvia (Lamiaceae) (Ebrahimi et al, 2014), with 57 sesterterpenoids isolated from 10 different Salvia species (Rustaiyan et al, 1982;Rustaiyan and Sadjadi, 1987;Rustaiyan and Koussari, 1988;Gonzalez et al, 1989;Moghaddam et al, 1995Moghaddam et al, , 1998Moghaddam et al, , 2010Topcu et al, 1996aTopcu et al, , 1996bUlubelen et al, 1996;Cioffi et al, 2008;Dal Piaz et al, 2009Ebrahimi et al, 2014;Moridi Farimani and Mazarei, 2014) and were reported to be present in two important food crops, wheat (Triticum aestivum) (Akihisa et al, 1999) and potato (Solanum tuberosum) (Toyoda et al, 1969). Plant sesterterpenoids have been shown to exhibit a broad range of biological activities, serving as insect antifeedant (Luo et al, 2010(Luo et al, , 2011(Luo et al, , 2013a(Luo et al, , 2013bLi et al, 2013) and antifungal (Luo et al, 2010;Li et al, 2013) agents, as cytostatic agents against human lung cancer cell (Rowland et al, 2001), as inhibitors of tubulin tyrosine ligase (Dal Piaz et al, 2009, as prolylendopeptidase inhibitors (Choudhary et al, 2004a), and as enhancers of interleukin-2 gene expression (Kawahara et al, 1999). However, our knowledge of sesterterpenoid biosynthesis and evolution in plants is rather limited, and genes and enzymes involved in plant sesterterpenoid formation have only very recently been reported from species of the Brassicaceae (Nagel et al, 2015;Wang et al, 2015).…”

“…Recently, we found that two Himalayan-Chinese species of the Lamiaceae, Leucosceptrum canum and Colquhounia coccinea var mollis, harbored two unique classes of defensive sesterterpenoids, namely, leucosceptroids and colquhounoids, respectively, which are closely related due to their common 5/6/5 core structure but are distinguished from each other based on differences in stereochemistry at C-6 and C-7 and later modifications (Luo et al, 2010;Li et al, 2013). Subsequent investigation led to the isolation and identification of over 100 defensive sesterterpenoids from the leaves and flowers of the above two plants (Luo et al, 2011(Luo et al, , 2013a(Luo et al, , 2013b.…”