To identify these adaptations, we have produced a library of ~70 genes which are switched on by dehydration in the bdelloid rotifer Adineta ricciae. The identity and function of these genes are currently under investigation, but we have focused initially on two genes which encode LEA proteins.
The two bdelloid LEA proteins are similar and probably derive from allelic gene copies but their sequences have diverged more than would be expected in alleles. Rotifers from class Bdelloidea are renowned for asexual reproduction, but they evolved from a sexual ancestor tens of millions of years ago (Mark Welch & Meselson 2000; Birky 2004). Asexuality, with concomitant lack of meiotic recombination, would allow former alleles to evolve independently and develop divergent sequences.
The sequence divergence of the A. ricciae lea genes has resulted in corresponding divergence of structure and function of the LEA proteins they encode. Thus, while the first protein, ArLEA1A, is unstructured and has a molecular shield function, the second protein, ArLEA1B, has some secondary structure and does not function as a molecular shield (see figure), but might instead have a role in membrane protection (Pouchkina-Stantcheva et al. 2007).
Bdelloid Rotifer Research Topics:
Birky C.W. Jr.(2004) Bdelloid rotifers revisited. Proc Natl Acad Sci USA 101: 2651-2652.
Mark Welch, D. and Meselson, M. (2000) Evidence for the evolution of bdelloid rotifers without sexual reproduction or genetic exchange. Science 288: 1211-1215.
Pouchkina-Stantcheva, N. N., McGee, B. M., Boschetti, C., Tolleter, D., Chakrabortee, S., Popova, A. V., Meersman, F., Macherel, D., Hincha D. K. and Tunnacliffe, A. (2007) Functional divergence of former alleles in an ancient asexual invertebrate. Science 318: 268-271.
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