Chitinases are a group of plant proteins that can deter herbivory and pathogens by hydrolyzing chitin in insect exoskeletons and fungal cell walls. During the evolution of plant carnivory, chitinase genes may have duplicated and diverged, giving rise to some that now function in carnivory. This project will advance understanding of the evolution of chitinase genes and carnivory in the Caryophyllales, one of the major plant groups that has evolved carnivory. This study will reconstruct an evolutionary history of carnivorous taxa, study divergence of chitinase genes, determine evolutionary selection among types of chitinases, and document their patterns of gene expression.
This study is the first to analyze the evolution of the chitinase gene family and it relationship with plant carnivory. In addition to improving understanding of the process of adaptive diversification of chitinase function, the results will provide scientific infrastructure in the form of increased understanding of relationships between taxa of Caryophyllales. The project also will provide mentoring and research-based training for undergraduates and will transmit information on carnivorous plants and their evolutionary biology to the general public.
Intellectual Merit: This research program has contributed to three areas of evolutionary biology: molecular evolution of gene families, systematics, and the study of adaptations at both macro (morphology) and micro (amino acid) levels. We took an integrative approach in studying adaptation by combining bioinformatics, phylogenetic inference, protein-specific divergence, and selection studies. Studying the evolution of digestive enzymes in relation to functionality at the molecular level. We studied the molecular evolution of digestive enzymes utilized in plant carnivory. A variety of enzymes are excreted from the carnivorous gland that aid in prey digestion. Within the carnivorous plants of the Caryophyllales, two subclasses of class I chitinases have been identified to play a role in the digestion of prey. Proteins produced by the large and diverse chitinase gene family are involved in the break down of chitin, a polymer of N-acetylglucosamines that make up the bulk of insect exoskeletons and fungal cell walls. Members of these chitinase subclasses, depending on the presence or absence of a C-terminal extension, can be secreted from specialized digestive glands found within the traps of carnivorous plants. We investigated the sequence homology among carnivorous plant class I chitinases and the method by which these enzymes have been adapted for the carnivorous habit. Novel class I chitinase homologs were recovered from Ancistrocladus, Dionaea, Drosera, Nepenthes, and Triphyophyllum, in addition to class I chitinases available from sequenced angiosperm genomes. Amino acid substitutions specific to carnivorous plant class I chitinases were revealed by detecting sites under positive selection. After examining the three-dimensional structure of the chitinases, these sites may confer functional differences. Our molecular evolution study of class I chitinases has been published in the journal Molecular Biology and Evolution (Renner & Specht, 2012). Combining morphological evolution with systematics. We also explored the phylogenetic relationships and morphological adaptations among carnivorous plant genera of the Caryophyllales. Taxonomic relationships across genera were refined and three strongly supported groups were identified: monophyletic Droseraceae (sundews and Venus-flytraps), Nepenthaceae (Asian pitcher plants), and a third clade containing Ancistrocladaceae, Dioncophyllaceae, and Drosophyllaceae (slobbering pines and non-carnivorous/part-time carnivorous plants). In combination with phylogenetic reconstruction, character mapping was utilized to assess evolutionary changes in the morphology of glands found on the leaf and involved in the digestion of prey. Adaptive changes resulting in the evolution of the carnivorous gland are described in detail within our manuscript accepted by the International Journal of Plant Sciences (Renner and Specht, 2011), and may be either the result of emargination of the leaf blade or homologous transformation of pinnae. Broader Impacts: Over the course this award, undergraduate students were mentored, all of which are women and/or historically underrepresented groups in biology, through research projects directly related to the proposal. These students include Ivet Ramirez-Oritz (UC Berkeley Biology Scholars Program, promoting economic, gender, ethnic and cultural groups underrepresented in biology), Josephine Wong (UC Berkeley SPUR student), Shayla Salzman (UC Berkeley). In addition, during January and February of 2011, Tanya Renner introduced lab techniques pertaining to carnivorous plant biology to visiting K-12 in the laboratory of Dr. Chelsea Specht. Topics included the history/background of molecular biology pertaining to the cell and DNA, carnivorous plant gland morphology, DNA, and the Polymerase Chain Reaction (PCR). Tanya Renner also demonstrated outreach through seminars and guest lectures specifically designed for the public to increase interest in science. In 2010, three public presentations were given: at the Bay Area Carnivorous Plant Society (Berkeley, CA), the San Diego Zoo Institute for Conservation Research (Escondido, CA), and the Bone Room, a natural history store (Albany, CA). Scientific research relating to the award was presented at the 2010 Evolution Meeting in Portland, OR.