Final Report Summary - EVO_FLORE (Evolution of floral size control in the genus Capsella)
Project context
A fascinating challenge in biology is to understand how the evolution of molecular mechanisms leads to phenotypic variation. In plants, a common trend of flower evolution is the reduction of floral display following the transition from out-breeding via animal pollinators to selfing. The genus Capsella is a genetically amenable model to dissect the genetic basis of this major trend. The selfing C. rubella, with its dramatically reduced flowers, evolved from C. grandiflora, an outbreeding species with large flowers.
Project objectives
The three major objectives of this fellowship were:
-1 to define the genetic basis of the selfing syndrome in the genus Capsella;
-2 to determine whether the selfing syndrome has evolved rapidly after the emergence of the selfing lineage;
-3 to understand the fitness consequences of the changed flower morphology.
Project results
(1)Genetics of flower size evolution:
The selfing syndrome is fixed in the C. rubella lineage, with the size of the petals having been reduced by shortening the period of cell proliferation. A quantitative trail locus (QTL) analysis on 142 recombinant inbred lines from a cross of C. rubella and C. grandiflora identified six large-effect QTL for petal size and one large-effect QTL for flower opening. Thus, the selfing syndrome has a complex genetic basis.
To identify the genes underlying the petal-size and petal-opening QTLs, heterogenous inbred families were generated for three petal-size QTLs and one petal-opening QTL. Fine mapping was done for the gene(s) underlying the petal-size QTL on chromosome G, delimiting the locus to a 700 kb interval. Thirty recombinants within this interval have been identified, and testing the segregation of petal size in their progeny will localise the causal mutation(s) to within a small interval of around 20 to 30 kb.
(2) History of selfing syndrome evolution:
To gain insight into the evolutionary history of the selfing syndrome, two experiments were performed: first, the segregation of selfing-syndrome traits was analysed in C. rubella intraspecific crosses. Secondly, a comparative QTL analysis was conducted using two different interspecific crosses. The results from both approaches strongly suggest that the evolution of the selfing syndrome has occurred relatively early before the geographical spread of the selfing species.
(3) Fitness consequences of the selfing syndrome:
Several hypotheses have been proposed to explain the evolution of the selfing syndrome. One scenario suggests that flower morphology has evolved to optimise the selfing capability of the plants. This hypothesis was tested by analysing the correlation between selfing syndrome traits and self-pollination efficiency (SPE) in our segregating population. This indicated a significant negative correlation between SPE and the petal-opening angle. In addition, the presumed ancestor of the Capsella rubella lineage was reconstructed by introducing its non-functional S-locus into C. grandiflora. The resulting plants resemble C. grandiflora, but are self-compatible; these had a selfing ratio two times lower than the modern C. rubella plants. Together, these results argue that the selfing syndrome has indeed evolved for reproductive assurance.
conclusions:
this fellowship has defined the basis of the selfing-syndrome evolution in Capsella at a developmental and genetic level, and has shed light on the evolutionary history and possible fitness consequences of this event. It has also contributed to generating highly valuable materials which will lead in the short term to the molecular dissection of selfing-syndrome evolution in this genus.
project impact:
the knowledge gained about the evolution of floral morphology following the breakdown of self-incompatibility in this genus improves our understanding about one of the most common trends in plant evolution. The materials and sequence information generated will be of general use for the plant research community.
A fascinating challenge in biology is to understand how the evolution of molecular mechanisms leads to phenotypic variation. In plants, a common trend of flower evolution is the reduction of floral display following the transition from out-breeding via animal pollinators to selfing. The genus Capsella is a genetically amenable model to dissect the genetic basis of this major trend. The selfing C. rubella, with its dramatically reduced flowers, evolved from C. grandiflora, an outbreeding species with large flowers.
Project objectives
The three major objectives of this fellowship were:
-1 to define the genetic basis of the selfing syndrome in the genus Capsella;
-2 to determine whether the selfing syndrome has evolved rapidly after the emergence of the selfing lineage;
-3 to understand the fitness consequences of the changed flower morphology.
Project results
(1)Genetics of flower size evolution:
The selfing syndrome is fixed in the C. rubella lineage, with the size of the petals having been reduced by shortening the period of cell proliferation. A quantitative trail locus (QTL) analysis on 142 recombinant inbred lines from a cross of C. rubella and C. grandiflora identified six large-effect QTL for petal size and one large-effect QTL for flower opening. Thus, the selfing syndrome has a complex genetic basis.
To identify the genes underlying the petal-size and petal-opening QTLs, heterogenous inbred families were generated for three petal-size QTLs and one petal-opening QTL. Fine mapping was done for the gene(s) underlying the petal-size QTL on chromosome G, delimiting the locus to a 700 kb interval. Thirty recombinants within this interval have been identified, and testing the segregation of petal size in their progeny will localise the causal mutation(s) to within a small interval of around 20 to 30 kb.
(2) History of selfing syndrome evolution:
To gain insight into the evolutionary history of the selfing syndrome, two experiments were performed: first, the segregation of selfing-syndrome traits was analysed in C. rubella intraspecific crosses. Secondly, a comparative QTL analysis was conducted using two different interspecific crosses. The results from both approaches strongly suggest that the evolution of the selfing syndrome has occurred relatively early before the geographical spread of the selfing species.
(3) Fitness consequences of the selfing syndrome:
Several hypotheses have been proposed to explain the evolution of the selfing syndrome. One scenario suggests that flower morphology has evolved to optimise the selfing capability of the plants. This hypothesis was tested by analysing the correlation between selfing syndrome traits and self-pollination efficiency (SPE) in our segregating population. This indicated a significant negative correlation between SPE and the petal-opening angle. In addition, the presumed ancestor of the Capsella rubella lineage was reconstructed by introducing its non-functional S-locus into C. grandiflora. The resulting plants resemble C. grandiflora, but are self-compatible; these had a selfing ratio two times lower than the modern C. rubella plants. Together, these results argue that the selfing syndrome has indeed evolved for reproductive assurance.
conclusions:
this fellowship has defined the basis of the selfing-syndrome evolution in Capsella at a developmental and genetic level, and has shed light on the evolutionary history and possible fitness consequences of this event. It has also contributed to generating highly valuable materials which will lead in the short term to the molecular dissection of selfing-syndrome evolution in this genus.
project impact:
the knowledge gained about the evolution of floral morphology following the breakdown of self-incompatibility in this genus improves our understanding about one of the most common trends in plant evolution. The materials and sequence information generated will be of general use for the plant research community.