Mechanisms of functional and physical genome reduction in photosynthetic and nonphotosynthetic parasitic plants of the broomrape family

Wicke S, Müller KF, dePamphilis CW, Quandt D, Wickett NJ, Zhang Y, Renner SS, Schneeweiss GM

Research article (journal)


Nonphotosynthetic plants possess strongly reconfigured plastomes due to convergent losses of photosynthesis and housekeeping genes, making them excellent study systems for studying genome evolution under relaxed selective pressures. We report the complete plasomes of ten photosynthetic and nonphotosynthetic parasites plus their nonparasitic sister from the broomrape family (Orobanchaceae). By reconstructing the history of gene losses and genome reconfigurations, we find that already the establishment of obligate parasitism triggers the relaxation of selective constraints. Partly due to independent losses of one inverted repeat region, Orobanchaceae plastomes vary 3.5-fold in size, with 45 kb in Conopholis representing the smallest plastome reported from land plants. Of the 42 to 74 retained unique genes, only 16 protein genes, 15 tRNAs, and 4 rRNAs are commonly found. Several holoparasites retain ATP synthase genes with intact open reading frames, suggesting a prolonged function in these plants. The loss of photosynthesis alters the chromosomal architecture in that recombinogenic factors accumulate, fostering large-scale chromosomal rearrangements as functional reduction proceeds. The retention of DNA fragments is strongly influenced by both their proximity to genes under selection and the co-occurrence with those in operons, indicating complex constraints beyond gene function that determine the evolutionary survival time of plastid regions in nonphotosynthetic plants.

Details zur Publikation

Pages: 15
Release year: 2013
Language in which the publication is writtenEnglish