Vergleichende Analysen zum plastidären Kodierungspotential und zur plastidären Genexpression von verschiedenen Arten der holoparasitisch lebenden Blütenpflanzengattung Cuscuta
The angiosperm genus Cuscuta (Cuscutaceae) comprises a range of species that have all adapted to a parasitic lifestyle in various degrees. The chlorophyllous, photosynthetically active species C. reflexa, the intermediate species C. gronovii and the white, achlorophyllous species C. odorata were analysed in this study. The influence of parasitism on the plastid coding capacity, the plastid transcriptional apparatus and plastid promoter structures were investigated. The plastid DNA of C. reflexa was partially cloned, sequenced and compared to the non-parasitic plant N. tabacum. The coding capacity of all Cuscuta species were analyzed by Southern blot hybridization using the plastid chromosome of N. tabacum as a reference. Although the plastid genome of the intermediate species C. gronovii has suffered extensive deletions, in constrast to the plastid genome of C. odorata it has retained photosynthesis related genes. Previous analyses had shown the deletion of subunits of the plastid encoded RNA-polymerase in C. gronovii and C. odorata. Promoter studies of the rbcL gene in green and intermediate species revealed the change of promoter sequences from PEP promoter to NEP promoter as a possible mechanism to retain the ability to photosynthesize. Analyses of RNA levels in all Cuscuta species and of transcript levels in C. reflexa revealed that a "parasite"-specific subset of RNA molecules is stabilzed in all species. The discripancy between run-on and steady-state analysis in C. reflexa might hint to alterations in RNA processing or transcript stabilization in this species.
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