patterns and contribute to understand the mechanistic bases for cospeciation. The
chemical profile of plants linked to host use and the correspondence of plants and
herbivores phylogenies documented for certain lineages are perhaps the best evidence supporting the cospeciation and codiversification patterns assumed by the
“escape and radiate” model of coevolution.
5.3
Biochemical Diversity
Secondary metabolites are functionally and structurally diverse organic molecules
not involved in primary metabolic functions of living organisms but involved in
more than one important biological process, usually related to survival and interaction with the environment [2, 171, 178]. In plants, secondary metabolites are
characterized by having low carbon content (less than 1%, [26]), being the nitrogen:carbon ratio crucial for secondary metabolism modulation (e.g., [63]). Since
deamination of amino acid phenylalanine that enabled the accumulation of simple
phenylpropanoids in early tracheophytes [182], products of secondary metabolism
of plants broadly diversified. Current diversity of phytochemical classes includes
steroids, terpenes, alkaloids, phenols, glucosinolates, glycosides, and also nonprotein amino acids and phytohormones [18, 185]. Secondary compounds are distributed in close to 302,211 species including vascular and nonvascular plants, from
which angiosperms represent close to 85% [33, 70, 163, 173]. Steroids and terpenes
(>30,000), along with phenols (>9000) and (>12,000) alkaloids are the most
structurally diverse classes of compounds. The first three have also the most ample
distribution in vascular plants [121].
In despite of molecule diversity, most secondary metabolites of plants have a
restricted taxonomic distribution, sometimes occurring only in particular genus or
botanical family (Table 3). Yet, chemically akin compounds can be found in distantly
related plant families (e.g., tropane alkaloids are common in Solanaceae but also
occur in Euphorbiaceae, Rhizoporaceae, and Convolvulaceae; [73]). However, the
machinery and pathways needed to produce different classes of compounds are
highly conserved [4, 186] and much less diverse than their resulting products
[179]. Three basic biosynthetic pathways are thought to be responsible for the
majority of phytochemicals. (1) The shikimic acid pathway is the biosynthetic
ä
Fig. 3 (continued) defenses. Species numbers and identification of clades are indicated in the
adjacent table. The branches in the Brassicales phylogeny are colored to indicate the origin of
indolic glucosinolates (purple), methionine-derived glucosinolates (green), and novel structural
elaborations to glucosinolates unique to the core Brassicaceae lineage (orange). Vertical dashed
lines indicate the origin of these novel chemical groups. Primary host-plant associations of several
Pierinae lineages are colored: orange (Brassicaceae), green (Capparaceae or Cleomaceae), orangegreen (mixture of previous), purple (more basal Brassicales that synthesize indolic glucosinolates),
blue (non-Brassicales feeding), and gray (unknown). The phylogenetic positions for the At-α and
At-β WGDs are depicted with white diamond symbols and significant net diversification rate shifts
with red star symbols. (Modified from Ref. [47])
60
E. Kariñho-Betancourt
chemical profile of plants linked to host use and the correspondence of plants and
herbivores phylogenies documented for certain lineages are perhaps the best evidence supporting the cospeciation and codiversification patterns assumed by the
“escape and radiate” model of coevolution.
5.3
Biochemical Diversity
Secondary metabolites are functionally and structurally diverse organic molecules
not involved in primary metabolic functions of living organisms but involved in
more than one important biological process, usually related to survival and interaction with the environment [2, 171, 178]. In plants, secondary metabolites are
characterized by having low carbon content (less than 1%, [26]), being the nitrogen:carbon ratio crucial for secondary metabolism modulation (e.g., [63]). Since
deamination of amino acid phenylalanine that enabled the accumulation of simple
phenylpropanoids in early tracheophytes [182], products of secondary metabolism
of plants broadly diversified. Current diversity of phytochemical classes includes
steroids, terpenes, alkaloids, phenols, glucosinolates, glycosides, and also nonprotein amino acids and phytohormones [18, 185]. Secondary compounds are distributed in close to 302,211 species including vascular and nonvascular plants, from
which angiosperms represent close to 85% [33, 70, 163, 173]. Steroids and terpenes
(>30,000), along with phenols (>9000) and (>12,000) alkaloids are the most
structurally diverse classes of compounds. The first three have also the most ample
distribution in vascular plants [121].
In despite of molecule diversity, most secondary metabolites of plants have a
restricted taxonomic distribution, sometimes occurring only in particular genus or
botanical family (Table 3). Yet, chemically akin compounds can be found in distantly
related plant families (e.g., tropane alkaloids are common in Solanaceae but also
occur in Euphorbiaceae, Rhizoporaceae, and Convolvulaceae; [73]). However, the
machinery and pathways needed to produce different classes of compounds are
highly conserved [4, 186] and much less diverse than their resulting products
[179]. Three basic biosynthetic pathways are thought to be responsible for the
majority of phytochemicals. (1) The shikimic acid pathway is the biosynthetic
ä
Fig. 3 (continued) defenses. Species numbers and identification of clades are indicated in the
adjacent table. The branches in the Brassicales phylogeny are colored to indicate the origin of
indolic glucosinolates (purple), methionine-derived glucosinolates (green), and novel structural
elaborations to glucosinolates unique to the core Brassicaceae lineage (orange). Vertical dashed
lines indicate the origin of these novel chemical groups. Primary host-plant associations of several
Pierinae lineages are colored: orange (Brassicaceae), green (Capparaceae or Cleomaceae), orangegreen (mixture of previous), purple (more basal Brassicales that synthesize indolic glucosinolates),
blue (non-Brassicales feeding), and gray (unknown). The phylogenetic positions for the At-α and
At-β WGDs are depicted with white diamond symbols and significant net diversification rate shifts
with red star symbols. (Modified from Ref. [47])
60
E. Kariñho-Betancourt