Research Fellows Directory
Sir David Baulcombe FRS
University of Cambridge
Progression in evolution requires that, occasionally, progeny are superior to their parents and that their improved characteristics are passed on to their descendants. In many instances this heritable progression may be due to random and spontaneous mutation. However we now have evidence that the heritable variation is induced by hybridisation of two organisms with a slightly different genome. The mismatch of DNA sequences in the two parents triggers molecular changes to the DNA of the hybrid so that the pattern of gene expression is different from that in the two parents.
Our findings, with interspecific hybrids of tomato and a wild relative, indicate a new role of regulatory RNA molecules known as small interfering (si)RNAs. These molecules were previously associated with genome defense against the effects of selfish DNA. However, in a variation of that idea, we propose that they allow differentiation of self from non self at the genome level. The siRNA from one genome interacts with the other and affects the pattern of gene expression. Our evidence also implicates epigenetic rather than genetic mechanisms in this non self differentiation. Epigenetic mechanisms do not change the sequence of A, C, G and T in DNA but they do affect the presence of methyl groups on C residues or the type of protein bound to a DNA and to its replication progeny.
These data provide an explanation of a phenomenon known to plant breeders as transgressive segregation in which the progeny of wide crosses may outperform the parents. These new findings will enable breeders to exploit transgressive segregation more effectively than in the past. They may also influence understanding of how evolution is facilitated because hybrids exploit existing heritable variation in a population and because their formation triggers new forms of heritable variation. Future work will explore the possibility that RNA has similar effects in animal hybrids.
Interests and expertise (Subject groups)