Sexual and genotypic variation in terpene quantitative and qualitative profiles in the dioecious shrub Baccharis salicifolia

Xoaquín Moreira,Ken Keefover-Ring,Kailen A Mooney,Jessica D Pratt,Colleen S Nell,Luis Abdala-Roberts,Carla Vázquez-González

doi:10.1038/s41598-019-51291-w

Abstract

Terpenoids are secondary metabolites produced in most plant tissues and are often considered toxic or repellent to plant enemies. Previous work has typically reported on intra-specific variation in terpene profiles, but the effects of plant sex, an important axis of genetic variation, have been less studied for chemical defences in general, and terpenes in particular. In a prior study, we found strong genetic variation (but not sexual dimorphism) in terpene amounts in leaves of the dioecious shrub Baccharis salicifolia. Here we build on these findings and provide a more in-depth analysis of terpene chemistry on these same plants from an experiment consisting of a common garden with male (N = 19) and female (N = 20) genotypes sourced from a single population. Our goal in the present study was to investigate quantitative and qualitative differences in terpene profiles associated with plant sex and genotypic variation. For this, we quantified leaf mono- and sesquiterpene amount, richness, and diversity (quantitative profile), as well as the composition of compounds (qualitative profile). We found no evidence of sexual dimorphism in monoterpene or sesquiterpene profiles. We did, however, find significant genotypic variation in amount, diversity, and composition of monoterpenes, but no effects on sesquiterpenes. These findings indicated that genotypic variation in terpene profiles largely surpassed variation due to sexual dimorphism for the studied population of this species.

Highlights

Terpenoids encompass a group of secondary metabolites which are often produced in high amounts in most plant tissues[1]
We build on these recent findings and provide a more in-depth analysis of terpene variation for these same plants from an experiment consisting of a common garden with male (N = 19) and female (N = 20) genotypes sourced from a single population of B. salicifolia[33]
We found no detectable effect of plant sex on richness, diversity or amount of either mono- or sesquiterpenes (Table 2, Fig. 1a–f)

Summary

Introduction

Terpenoids encompass a group of secondary metabolites which are often produced in high amounts in most plant tissues[1]. Despite mounting evidence of sexual dimorphism in traits associated with resistance to herbivory, including plant physical defences (e.g. spines[29], leaf toughness30) and secondary chemistry (e.g. phenolic compounds[28,30] or coumarins31), few studies have tested for effects of plant sex on terpenes[32,33]. There are a number of studies measuring the effects of plant sex on quantitative variation in chemical defences, including terpenes[32,33], fewer have tested for effects on compositional variation or assessed the effects of plant sex relative to other sources of genetic variation. By replicating multiple genotypes within each sex, we are able to compare the effects of plant sex vs. those due to additional genotypic variation, and in doing so provide a unique assessment of multiple sources of genetic variation in quantitative and qualitative terpene expression

Methods

Results

Conclusion