Research Projects
Evolution of carnivorous plants
Carnivorous plants are able to attract, trap, digest, and absorb insects captured by their specialized leaves. They arose from non-carnivorous ancestors. However, their evolutionary processes remain unclear. I am studying morphological and functional evolution of carnivorous plant by comparative approaches which include:
Interspecies comparison between carnivorous and non-carnivorous plants
Comparative analysis of carnivorous and non-carnivorous leaves in a single species by taking advantage of phenotypic plasticity.
Detecting evolutionary trends among independently evolved carnivorous plant lineages
For detail, see below.
Pitcher leaf development
Although successive phenotypic changes are explained by the accumulation of mutations, how drastic morphological evolution is attained remains unclear. In the evolution of carnivorous plants, an ancestral flat leaf was modified into a complex pitcher shape. To understand the developmental mechanisms of pitcher leaves, I analyzed leaf development of American pitcher plant Sarracenia purpurea. Although such developmental modifications have been believed to be achieved by changes in adaxial-abaxial polarity in early leaf development, the pitcher leaves showed standard expression patterns of adaxial and abaxial marker genes. Instead, pitcher primordia developed through a differently oriented cell division in adaxial tissues. This work provided previously undescribed mechanisms of drastic morphological evolution through tissue-specific changes in cell division orientation.
The genome and trap leaf evolution in Cephalotus follicularis
To find a clue to genetic bases of pitcher leaf evolution, we sequenced the nuclear genome of the Australian pitcher plant Cephalotus follicularis in collaboration with an international team. This plant produces both carnivorous pitcher and non-carnivorous flat leaves, enabling us to deduce the morphological and functional evolution by comparative approaches in a single species. We developed culture methods to control the developmental fates of the two types of leaves and established a gene-silencing method in vivo. Using these newly developed techniques in combination with the genomic information, we identified genes that are associated with different aspects of plant carnivory. We are characterizing the genes to understand the evolution of carnivorous plants.
Repeated evolution of digestive enzymes
Carnivorous plants independently arose in five orders of flowering plants; hence, they independently acquired digestive enzymes to degrade insect bodies. However, functional origins and evolutionary processes of digestive enzymes remained unknown. We are working on this issue by genomic and phylogenetic approaches.
Adaptive molecular convergence
Convergence, in which phenotypic similarities independently arise in different organisms, is a common evolutionary process across the entire tree of life. Phenotypic convergence is often caused by identical genetic changes called adaptive molecular convergence. This evolutionary pattern suggests that a limited number of molecular evolutionary pathways are accessible to attain a novel phenotype under certain selective pressures. However, the molecular mechanisms through which adaptive molecular convergence is driven remain unclear. In this project, I aim to unravel how evolutionary pathways are constrained at the molecular level by developing a computational framework to perform a genome-wide scan of convergent genetic changes and by analyzing how protein properties limit patterns of molecular evolution.
csubst – a tool for molecular convergence detection in DNA/codon/protein sequences
Karyotype-informed molecular phylogeny
Elucidation of the phylogenetic relationship is a prerequisite for the study of evolutionary biology. To infer the evolutionary processes, I reconstructed phylogenetic relationships of several flowering plant taxa that have characteristic functional traits like carnivory. To identify polyploidization events, which introduce a bias to phylogenetic inference, I also analyzed karyotypes. Karyotype-informed phylogenetic relationships revealed key evolutionary events of carnivorous plants as well as other taxa: e.g. patterns of trait evolution, inter-species hybridization, changes of geographical distribution, chromosomal rearrangements, and so on.
