The Distribution Patterns Of Secondary Metabolites In The Tree Of Life Of The Seed Plants

Plant secondary metabolites(PSMs),as ubiquitous low molecular-weight compounds that are not involved in resource acquisition or allocation,are the significant chemical evidence to study on the plant phylogeny in in-depth exploration.In recent decade,ultilizing multiple phylogenetic comparative methods to understand the distribution and evolutionary patterns of the PSMs across the tree of plant has been the frontier research of evolutionary biology based on intergrating multidisciplinary research(e.g.,plant systematics and phytochemistry).The question about how secondary metabilites distribute and evolve across tree of life of plants have been the alluring focus to botanical systematists and phytochemists since last several decades,such as Cronquist(1977)proposed the hypothesis that the related plant group in same age share similar PSMs.But to date,testing whether Cronquist' s hypotheses is valid and the distribution of PSMs across seed plant phylogeny remains imperfectly known.With the availability of the tree of spermatophytes and discovery and identification of a large amount of the plant secondary metabolites(more than 100,000 natural products),it is possible for us to carry out such exploration this day.In this research,we selected 8 classes of PSMs[alkaloids,phenolic acids,flavonoids,tannins,terpenoids,lignans and coumarins(L&Cs),quinones and steroids]and mapped them onto the best current phylogenetic estimates of relationships among 437 families of extant seed plants.We found that the PSMs data in 308 families were available,and 129 families(mainly some unusual families like Amborellaceae)have not reported.And two kinds of PSMs that flavonoids and alkaloids distributed in seed plants widely,there were 245 families reported contain flavonoids and 221 families contain alkaloids,the quinones,tannins,phenolic acids,L&Cs and steroids were patchily distributed in the phylogenetic trees of seed plant.To further understanding the distribution patterns of PSMs across tree of seed plants,we performed the two latest methods of Blomberg's K value and D value to calculate the phylogenetic signals.The results indicated that there were significant phylogenetic signals in all PSMs classes except steroids.For phylogenetic signal is the tendency of related species to resemble each other with respect to evolutionarily related traits more than would be expected for species drawn at random from a phylogenetic tree,our result indicated that 7 classes of PSMs were clustered in phylogeny of seed plant,and steroids was random distribution,and all of which also affirmed the hypothesis that proposed by Cronquist(1977).The phylogenetic signal of 7 classes of PSMs in whole seed plant were weak to moderate(0<K<1or0<D<1),suggest strong diversifying selection during seed plant diversification,and/or relatively weak evolutionary constraints on PSMs(i.e.the diversification of PSMs were affected by environmental factor effectively).We also tested 8 classes of PSMs for phylogenetic signal within 54 major clades of seed plants.We found that 7 classes of PSMs(except steroids)show phylogenetic signal in 18 clades of seed plant,in gymnosperms only terpenoids found phylogenetic signal,in angiosperms there was no significant phylogenetic signal detected in basal clades of angiosperm and monocots,phylogenetic signal of 7 classes PSMs mainly found in 13 clades of core Eudicots(Superasteridae and Superrosidae).All of which means external factors(such as environmental,ecological and biological factors)were more effective than genetic heredity in the evolution of PSMs diversity.These 18 clades that have phylogenetic signals were closely related to the diversity of PSMs,which means that there was co-diversification between them in history of evolution.In the view of their origin,most PSMs have emerged in the ancestral group of seed plants,but diversified tremendously due to the explosion of angiosperm diversity,like flavonoids had been present in early land plants but widely distributed and showed diversity only in seed plant.Moreover,our results suggest that PSM diversification may have been an important factor in promoting the diversification of insects,mammals and birds during and after the Cretaceous,for example,the emergence of stigma and the transformation of volatile terpenes from allomones to kairomones or synomones are the main reasons for the transformation of herbivorous insects into pollinators.Our results of certain PSM were clustered in related plant group,the distribution characteristics of PSMs in the tree of life and the phylogenetic signals of PSMs have important potential and prospects for the search for natural compounds,finding new potentially drug-producing groups of plants,and certainly in searching for specific PSMs in related plants.