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Professor of Plant Biology
Department of Plant Biology Plant Biology Department
Selected Recent Publications; Publication List; Current Funding; Teaching; Lab Members; Lab website |
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Research
Research in the Sears lab has focused on the genetics, evolution, and molecular biology of the DNA-containing organelles.
Individual research projects have investigated the controls of chloroplast DNA replication, the inheritance of chloroplasts, nuclear genes that affect the fidelity of chloroplast and mitochondrial DNA maintenance, and organelle mutation events, particularly replication slippage, in an evolutionary context.
Chloroplast DNA is remarkably conservative in an evolutionary sense, with genes governed by a slower "molecular clock" than are nuclear genes. This observation implies that the enzymes of chloroplast DNA replication and repair function efficiently to maintain a high level of fidelity in the maintenance of the chloroplast genome. To study the mutation process, we have used the unicellular green alga Chlamydomonas reinhardtii because its small size allows billions of cells to be analyzed in a single experiment. In studying spontaneous mutations in the chloroplast DNA, we have observed a predominance of transversions over transitions, with the mutations resembling those that would be caused by oxidative damage. We hypothesize that under the high light growth conditions experienced by our Chlamydomonas cell lines, the chloroplast DNA repair systems may not have been able to handle all of the damage caused by the oxygen generated by the water-splitting activity of photosynthesis. This hypothesis is currently being tested by analyzing spontaneous mutations that occur under conditions of heterotrophic growth, in low light.
In both Chlamydomonas and Oenothera (the evening primrose), we have examined the instability of chloroplast DNA microsatellites, which are composed of short direct repeated sequences. Short direct repeats are known to be prime substrates for replication slippage, which results in duplication or deletion of one or more repeats during transient dissociation of the replication complex. We have found that chloroplast microsatellites undergo mutation by duplication or deletion of repeats about 1000x more frequently than individual nucleotides of the chloroplast DNA experience base substitution. Current studies are directed at identifying the components of the chloroplast replication and repair machinery that act to minimize both of these types of mutation.
Another project involves the manipulation of levels of homologous recombination in plant mitochondria, as we seek to determine if homologous recombination is the process responsible for creating debilitating rearrangements of mitochondrial DNA, which cause plant developmental abnormalities such as cytoplasmic male sterility. This project has used Arabidopsis and Nicotiana as the experimental organisms of choice, with the introduction of an E. coli recA gene into the plant nucleus, with a mitochondrial-targeting sequence.
GuhaMajumdar, M and BB Sears. 2004. Chloroplast DNA base substitutions: an experimental assessment. Mol. Gen. Genomics, in press.
GuhaMajumdar, M, S Baldwin, and BB Sears. 2004. Chloroplast mutations induced by 9-aminoacridine hydrochloride are independent of the plastome mutator in Oenothera. Theor. Appl Genet 108 (3):543 - 549
Riekhof, WR, ME Ruckle, TA Lydic, BB Sears, C Benning. 2003. The sulfolipids 2'O-acyl-sulfoquinovosyldiacylglycerol and sulfoquinovosyldiacylglycerol are absent from a Chlamydomonas reinhardtii mutant deleted in SQD1. Plant Physiol 133:864-874
Hupfer, H., M. Swiatek, S. Hornung, R. G. Herrmann, R. M. Maier, W.-L. Chiu, and B.B. Sears. 2000. Complete nucleotide sequence of the Oenothera elata plastid chromosome, representing plastome I of the five distinguishable Euoenothera plastomes. Mol Gen Genet 263:581-585.
2000-04 NSF Competitive Grant: "Chloroplast Microsatellite Mutators
2004-5 MSU College of Natural Science
ZOL/PBL 341 - Fundamental Genetics
Every fall
GEN 810 - Theory & Practice of Teaching Genetics
Every fall
Undergraduate research projects (BMB 499, NSC 498, PLB 495)
Robin Pregitzer, undergraduate researcher
James Kelly, undergraduate researcher
Keith Christofferson, undergraduate assistant
Former Graduate Students:
Sara A. Kaplan
Wan-Ling Chiu
Pung-Choo Lee
Ellen M. Johnson
Mireille Khairallah
Wan-Ling Chiu
Pyung-Ok Lim
Susan Baldwin
Tseh-Ling Chang
Lara Stoike
Monica Guha-Majumdar
Elaine Palucki
Former Technicians:
Neta Holland
Gabi Schewe
Former Postdoctoral Associates:
Linda Schnabelrauch
Ruth Wolfson
Richard Glick
Karen Toth
David Jarrell
Kranthi Paladugu
Current Collaborators at MSU:
Christoph Benning, Biochemistry & Molecular Biology
Andrea Braeutigam (Genetics Program) and Andreas Weber, Plant Biology
Current Collaborators from outside MSU:
Karen VanWinkle-Swift, Northern Arizona University, Flagstaff
Alberto Prina, Instituto Genética, CNIA, Buenos Aires, Argentina
