The genetic architecture of petal number in Cardamine hirsuta

Abstract

SummaryInvariant petal number is a characteristic of most flowers and is generally robust to genetic and environmental variation. We took advantage of the natural variation found in Cardamine hirsuta petal number to investigate the genetic basis of this trait in a case where robustness was lost during evolution.We used quantitative trait locus (QTL) analysis to characterize the genetic architecture of petal number.Αverage petal number showed transgressive variation from zero to four petals in five C. hirsuta mapping populations, and this variation was highly heritable. We detected 15 QTL at which allelic variation affected petal number. The effects of these QTL were relatively small in comparison with alleles induced by mutagenesis, suggesting that natural selection may act to maintain petal number within its variable range below four. Petal number showed a temporal trend during plant ageing, as did sepal trichome number, and multi-trait QTL analysis revealed that these age-dependent traits share a common genetic basis.Our results demonstrate that petal number is determined by many genes of small effect, some of which are age-dependent, and suggests a mechanism of trait evolution via the release of cryptic variation.

Seasonal Regulation of Petal Number

“…In addition to this seasonal trend, we had previously described a temporal trend in petal number during plant ageing in C. hirsuta Pieper et al, 2016). We found that average petal number per flower also declined as the plants aged in field conditions (denoted by floral node number, Fig.…”

“…Therefore, early flowering did not strictly associate with more petals per flower. Moreover, at least 15 QTL have been detected where natural allelic variation affected petal number in C. hirsuta, and few of these colocated with flowering time QTL (Cartolano et al, 2015;Pieper et al, 2016). Interpreting our results in the context of seasonal variation, we suggest that certain environmental conditions associated with spring flowering in our field experiments, such as cool daily temperatures and extended vernalization, may act together to promote petal formation.…”

“…We found that average petal number per flower also declined as the plants aged in field conditions (denoted by floral node number, Fig. 1M), similar to greenhouse-grown plants Pieper et al, 2016). This trend was apparent in the C. hirsuta Ox accession, irrespective of whether the plants flowered in spring or summer (Fig.…”

“…This robustness is lost in C. hirsuta, resulting in a variable number of petals per flower Pieper et al, 2016). We have shown that this phenotype is influenced by both genetic variation and here, by environmental variation.…”

Elena M. Kramer

“…I have really enjoyed Angela Hay's work on diverse problems in Cardamine , including explosive seed dispersal (Hofhuis & Hay, ) and variation in petal number (Pieper et al ., ). They are two completely different developmental phenomena but both the papers apply cutting‐edge approaches, from biophysics to quantitative trait loci, to their exploration.…”