Heritability of floral volatiles and pleiotropic responses to artificial selection in Brassica rapa

Abstract

SummaryThe evolution of the vast diversity of floral volatiles is little understood, although they serve fundamental functions, such as pollinator attraction and herbivore deterrence. Floral volatiles are often species specific, yet highly variable and sensitive to environmental factors. To date, nothing is known about the heritability of floral volatiles, and whether individual compounds can evolve independently or solely in concert with the whole volatile bouquet.We conducted bi-directional artificial selection on four target floral volatiles to estimate heritability and correlated pleiotropic responses in the wild turnip (Brassica rapa).The realized heritability of the four target volatiles ranged from 20% to 45%. The average narrow-sense heritability of all 13 analyzed floral volatiles was 18% based on parent-offspring regressions. There were pleiotropic effects of the selected floral volatile compounds on other constituents of the floral scent bouquet, on flowering time and on some morphological traits. We found that the whole floral scent bouquet changed, even when there was selection only on single compounds, with the overall phenotypic covariance being unaffected.Our study demonstrates that floral scent can evolve rapidly under phenotypic selection, but with additional correlated responses in traits that are not direct targets of selection.

The molecular bases of floral scent evolution under artificial selection: insights from a transcriptome analysis in Brassica rapa

“…Evolutionary change in non-selected VOCs can be explained by pleiotropy or close linkage between individual “scent genes” (linkage disequilibrium). These mechanisms were previously suggested to contribute to the evolution of scent bouquets19. The transcriptome data of the high and low selection line plants render us the possibility to unravel the molecular mechanisms of these phenomena.…”

“…19. 50 seeds from ten individuals (5 seeds per each mother plant) of third generation plants for both “high” and “low” selection lines were sown out in standardized soil (Humuswerke Gebr.…”

“…Fast cycling Brassica rapa (Wisconsin fast plants) is a strain with short life cycle and thus an ideal model for artificial selection studies (http://fastplants.org). Such an experiment has recently been carried out to assess the heritability of flower scent with four different scent compounds as selection targets19. In their study, three generations of artificial selection lead to significant scent divergence between “high” and “low” selection line plants.…”

Interpopulation variation in pollinators and floral scent of the lady’s-slipper orchid Cypripedium calceolus L.

“…As with other floral traits, floral scents are known to vary within species, both within and among populations (Dötterl et al 2005;Chartier et al 2013;Mant et al 2005;Stökl et al 2009;Sun et al 2014), and this variability is strongly suggested to have a genetic basis (e.g., Andargie et al 2014;Friberg et al 2013;Zu et al 2016). However, little is known whether such genetic variability is the result of divergent selection or other scenarios (e.g., drift).…”

Genetic Analysis of Natural Variation in Antirrhinum Scent Profiles Identifies BENZOIC ACID CARBOXYMETHYL TRANSFERASE As the Major Locus Controlling Methyl Benzoate Synthesis

“…In Antirrhinum the gene COMPACTA is involved in maintenance of B function affecting petal size and scent emission (Manchado-Rojo et al, 2012). A study of narrow sense heritability in Brassica rapa has shown that although scent profiles between species differ in many cases in a number of independent VOCs, they may have coregulation between them and with other morphological traits or flowering time (Zu et al, 2016). The genes involved in single compound biosynthesis together with regulatory loci with several genetic functions indicates that the natural variation of scent emission may identify both regulatory loci as in Petunia and structural genes involved in discrete VOCs biosynthesis, or form part of larger pathways, affecting downstream products.…”