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SUMMARY:Evolution of vitamin B12 auxotrophy determined by methionine synth
 ase isoform - Katherine Helliwell
DTSTART:20100521T120000Z
DTEND:20100521T123000Z
UID:TALK23961@talks.cam.ac.uk
CONTACT:15560
DESCRIPTION:Many organisms require vitamins because they provide the precu
 rsors to essential enzyme cofactors important for metabolism. The requirem
 ent for vitamin B12 differs between diverse groups of organisms. For insta
 nce\, higher plants and fungi do not require B12\, whereas animals do. Wit
 hin the algal kingdom\, the requirement for B12 differs between closely re
 lated species\, so these organisms are an interesting group to focus on to
  try to understand how vitamin auxotrophy may have evolved. In algae vitam
 in B12 is an essential cofactor for methionine synthase (METH)\, which is 
 involved in the synthesis of methionine. However\, there is an alternative
  isoform of methionine synthase (METE)\, which catalyses the same reaction
  but without B12. I set out to determine the cellular mechanisms underlyin
 g the evolution of vitamin B12 dependence in algae and have compared eleme
 nts of B12 metabolism in 15 algal species with sequenced genomes. It appea
 rs that the methionine synthase isoform is a key determinant in the evolut
 ion of vitamin B12 auxotrophy in algae. Furthermore through studies of phy
 siology and gene regulation\, we have accumulated data that points to mult
 iple losses of METE as being a key factor in the evolution of B12 dependen
 ce in algae. Evidence in support of this theory includes the identificatio
 n of a METE unitary pseudogene in Volvox carteri\, a close relative of C. 
 reinhardtii\, which suggests that B12 dependence evolved relatively recent
 ly in this lineage. Moreover\, the observation that METE expression is rep
 ressed by vitamin B12 in a marine diatom\, Phaeodactylum tricornutum\, pro
 vides a mechanism for gene loss and helps to explain the likely cause for 
 the evolution of B12 dependence in algae. Finally\, I aim to transform V. 
 carteri with METE from C. reinhardtii to see if this will rescue its B12-d
 ependent phenotype. Given that eukaryotes must obtain vitamin B12 from pro
 karyotes\, the selective loss of METE in different algal species may have 
 had important physiological and ecological consequences for these lineages
 .
LOCATION:Department of Plant Sciences\, Large Lecture Theatre
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