Systematics and plastid genome evolution in the parasitic plant genus Cuscuta (Dodder)

• Main Author: McNeal, Joel R
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2005
• Subjects: Botany
• ISBN: 9780549002468; 0549002464

Parasitism has evolved independently many times within the course of angiosperm evolution. One of the most economically damaging of these parasitic lineages is the genus Cuscuta, which is derived from within the Morning Glory Family (Convolvulaceae). All species of Cuscuta are epiphytic stem parasites that lack roots and expanded leaves at maturity. Their hosts include a wide array of non-grass land plants, and a single Cuscuta individual may parasitize dozens of host species simultaneously. Although almost 200 described species exist, identification and taxonomy are difficult within the genus, as few morphological characteristics exist outside of the inflorescence in these reduced parasites. Although only about 10% of the genes necessary for photosynthesis are transcribed from the plastid chromosome, analyses of plastid genome structure, gene content, and sequence evolution are an excellent and efficient way to study the changes in photosynthetic ability and organellar function that accompany the transition from autotrophy to heterotrophy in angiosperms. This work presents a useful method for acquiring complete plastid genome sequences from parasitic plants, analyses of full plastid genome sequences from two Cuscuta species and a nonparasitic relative, and a well-resolved and highly-supported phylogeny of Cuscuta using 3 plastid genes (rbcL, rps2, and matK) and the nuclear ribosomal internal transcribed spacer locus. A molecular phylogenetic approach is used to address hypotheses involving taxonomy, biogeography, morphological evolution, photosynthetic ability, and plastid genome evolution within the genus.