Polymethylated Myricetin in Trichomes of the Wild Tomato Species Solanum habrochaites and Characterization of Trichome-Specific 3′/5′- and 7/4′-Myricetin O-Methyltransferases      

Abstract

Flavonoids are a class of metabolites found in many plant species. They have been reported to serve several physiological roles, such as in defense against herbivores and pathogens and in protection against harmful ultraviolet radiation. They also serve as precursors of pigment compounds found in flowers, leaves, and seeds. Highly methylated, nonglycosylated derivatives of the flavonoid myricetin flavonoid, have been previously reported from a variety of plants, but O-methyltransferases responsible for their synthesis have not yet been identified. Here, we show that secreting glandular trichomes (designated types 1 and 4) and storage glandular trichomes (type 6) on the leaf surface of wild tomato (Solanum habrochaites accession LA1777) plants contain 3,7,3#-trimethyl myricetin, 3,7,3#,5#-tetramethyl myricetin, and 3,7,3#,4#,5#-pentamethyl myricetin, with gland types 1 and 4 containing severalfold more of these compounds than type 6 glands and with the tetramethylated compound predominating in all three gland types. We have also identified transcripts of two genes expressed in the glandular trichomes and showed that they encode enzymes capable of methylating myricetin at the 3# and 5# and the 7 and 4# positions, respectively. Both genes are preferentially expressed in secreting glandular trichome types 1 and 4 and to a lesser degree in storage trichome type 6, and the levels of the proteins they encode are correspondingly higher in types 1 and 4 glands compared with type 6 glands.

Assessing the Biosynthetic Capabilities of Secretory Glands inCitrusPeel

“…A gene of the CYP82C subfamily, members of which have been demonstrated to be involved in the biosynthesis of 5-hydroxylated coumarins (Kruse et al, 2008), was found to be highly enriched in ECs (Table II). Polymethoxylated flavonoids are formed by successive hydroxylations and O-methylations (Willits et al, 2004;Schmidt et al, 2011), and candidate genes for enzymes involved in these steps were also found to be highly enriched in ECs (Supplemental Table S5). These observations indicate that our gene expression data from Citrus glandular ECs reflect their specialization for essential oil biosynthesis and present an excellent resource for gene discovery related to the biosynthesis of oil constituents.…”

Metabolomics reveals organ-specific metabolic rearrangements during early tomato seedling development

“…For any organ where a metabolite was absent or excluded in more than 15 out of the total of 45 Strack et al (1987) b Moco et al (2006) c Iijima et al (2008) d Vallverdu-Queralt et al (2010) e Tikunov et al (2010) f Gómez-Romero et al (2010) g Ferreres et al (2010) h Butelli et al (2008) i Bovy et al (2002) j Schmidt et al (2011) samples, this metabolite was removed from the mixed model analysis. The number of metabolites analysed for each organ is indicated in Supplementary Table S4.…”

“…In addition, compounds described in the literature to be present in WT tomato fruits (Gómez-Romero et al 2010;Tikunov et al 2010;Vallverdu-Queralt et al 2010), transgenic tomato fruits (Butelli et al 2008), transgenic tomato seedlings (Bovy et al 2002), tomato seeds (Ferreres et al 2010) and tomato leaves (Strack et al 1987;Lawson et al 1997;Schmidt et al 2011) were incorporated into the list of known tomato compounds. New metabolites were putatively annotated based on their elemental formulae calculated from the observed accurate mass and using additional information such as UV absorption spectra and high-mass resolution fragmentation data.…”

Analysis of Natural and Induced Variation in Tomato Glandular Trichome Flavonoids Identifies a Gene Not Present in the Reference Genome

“…Flavonols, a subclass of flavonoids, include kaempferol, quercetin, and myricetin (the structure of myricetin is shown in Figure 1) and are relatively widespread and abundant in plants (Herrmann, 1976). Flavonols are typically found as modified compounds, with glycosylation and methylation of the various hydroxyl groups commonly observed (Stevens et al, 1995;Braca et al, 2001;Schilmiller et al, 2010a;McDowell et al, 2011;Schmidt et al, 2011). Chemical modifications are known to affect the physical properties and chemical reactivity of flavonoids.…”

“…Plants contain little, if any, nonmodified myricetin (reviewed in Schmidt et al, 2011;Schmidt et al, 2012). Nonglycosylated myricetin is always methylated at the 3-hydroxyl (-OH) position ( Figure 1) and may be methylated at other hydroxyl positions as well.…”