Presentation on theme: "The exam was written based on 100 points. Dr. Cline will weight its contribution to your final grade based on the fact that the exam covers material presented."— Presentation transcript:
The exam was written based on 100 points. Dr. Cline will weight its contribution to your final grade based on the fact that the exam covers material presented in 6 classes. Important – please keep your answers short; confine your answers to the space provided; do not write on the back of any pages ! PCB6528 Spring Exam 2 – Chase Name ____________________________ Page 1 of 4 1 (24 pt) The following statements relate to our class discussion of organelle genomes. For each statement, indicate whether the statement applies to the plastid genome (pt), the plant mitochondrial genome (mit), both plastid and plant mitochondrial genomes (both), or neither of these genomes (none). Circular maps based upon DNA sequencing Linear and circular molecules of various sizes visualized by FISH or EM Subgenomic forms mediated by recombination through direct repeats Inversion isomers mediated by recombination through inverted repeats Gene order is generally conserved among plant species Gene order is highly variable among plant species Gene coding content varies among plant species Genome can be genetically transformed through homologous recombination
Modified from Timmis et al. Nat Rev Genet 5:123 A construct that consists of chloroplast sequences (C and D) that flank two selectable marker genes is inserted into the chloroplast genome through homologous recombination, thereby transforming the native plastome into a TRANSPLASTOME (a). One of the selectable genes (aadA) is designed for exclusive expression in the chloroplast and incorporation of this marker confers spectinomycin resistance. The other gene, a neomycin phosphotransferase gene neoSTLS2, includes a nuclear promoter and contains a nuclear intron within the reading frame. NeoSTLS2 confers kanamycin resistance only when it is transposed to the nucleus. Continuous selection of growing leaf cells on spectinomycin medium allows transformed plastomes to be selected and eventually the transplastome entirely replaces the native chloroplast genome, such that all copies of the chloroplast genome contain the two selectable marker genes (b). The transplastomic plants were crossed with wild-type female plants. Because of strict maternal inheritance of tobacco plastids, progeny that contained only wildtype chloroplasts were produced. Selection of progeny seedlings on kanamycin medium allows the detection of the rare cases in which the neo gene has changed its location, such that strong expression is promoted from the nuclear environment (c). Therefore, chloroplast-to-nucleus transposition must have occurred at some stage during the life cycle of the male parent of the seedlings that were recovered on kanamycin plates. The observation that 1 in 16,000 male tobacco gametes contained a segment of chloroplast DNA newly integrated into the nuclear genome was unpredictably high. PCB6528 Spring Exam 2 – Chase Name ____________________________ Page 2 of 4 2 (24 pt) In our discussion paper we saw that plastid genome transformation could be used to genetically mark plastid genomes so that we could follow their fate in grafting experiments. In the experiment described below, genetically marked plastids were used to monitor the transfer of plastid DNA to the nucleus. Explain why this experiment estimates only the frequency of non- functional DNA transfer from plastid to nucleus, rather than the frequency of a plastid gene undergoing a transfer such that its gene function is re-established from the nucleus.
PCB6528 Spring Exam 2 – Chase Name ____________________________ Page 3 of 4 3 (21 pt) The following statements relate to our class discussion of organelle gene expression. For each statement, indicate whether the statement applies to the plastids (pt), the plant mitochondria (mit), both plastid and plant mitochondria (both), or neither organelle (none). Genes are transcribed by single-subunit, bacteriophage-type RNA polymerases Genes are transcribed by multi-subunit, bacterial-type RNA polymerases Transcription utilizes nuclear-encoded sigma factors Primary transcripts are multi-cistronic operons Genes contain group II introns that undergo self-splicing in the organelle Site-specific RNA binding proteins of the PPR class are involved in multiple gene expression processes Primary transcripts must undergo C-to-U RNA editing to correct DNA coding errors
PCB6528 Spring Exam 2 – Chase Name ____________________________ Page 4 of 4 4 (31 pt) In the two experiments shown below, Schult et al (Plant Cell 19:1329) investigated the effects of the hcf173 mutation on the thylakoid proteins of Arabidopsis. What does hcf stand for AND why would the authors expect to see differences in the thylakoid proteins of the hcf mutant compared to wild-type plants? Based on the immunoblotting experiment (below, left): Which thylakoid protein complex appears to be most strongly affected in this mutant? Explain your reasoning. Based on the in vivo protein synthesis experiment (below, right), which plastid gene/protein appears to be the one most directly affected by the mutant? Explain your reasoning. Based upon your answers above and our class discussions, what aspect of plastid gene expression would you next investigate to determine the primary function of the hcf173 gene with respect to plastid gene expression. Explain your reasoning. Above - In Vivo Protein Synthesis in Wild- Type Plants and hcf173 Mutants. Newly synthesized proteins of 15-d-old plants were radiolabeled with 35S-Met for 20 min. (A) Wild-type and hcf173 membrane proteins with equivalent amounts of radioactivity (100,000 cpm) or the indicated dilutions were separated by SDS-PAGE and analyzed by fluorography. Left - Immunoblot Analysis of Thylakoid Membrane Proteins from the Wild Type and the Mutant hcf173. Twenty micrograms (WT 1/1 and hcf173), 10 mg (WT 1/2), 5 mg (WT 1/4), and 2.5 mg (WT 1/8) of protein were separated by SDS-PAGE and transferred to a nitrocellulose membrane. Specific proteins were immunodecorated with the indicated antisera.