Duplication Allows Divergent Evolutionary Fates of Gene Function in Legumes

Genes often become duplicated. Once duplicated, they can have different functional evolutionary fates. Genes can either loose, retain, or take on new function. Here we illustrate these outcomes based on several genes involved in legume nodulation. For example, duplicated CLE genes involved in early nodulation control have diversified to be either involved in inoculation-related long-distance control, or short distance, localised nitrate control of nodule numbers (see (1) and Functional Genomics Workshop). It is presumed that the CLE peptide is recognised by an LRR-RK structurally related to CLV1 in Arabidopsis, called GmNARK. This GmNARK gene is duplicated as GmCLV1A, whose function is not in nodulation control but maintenance of nodal identity (see S. Mirzaei talk). Here we see a neodiversification, possibly from the ancestral GmCLV1A gene towards the nodulation-specific GmNARK. Nodulation is initiated by Nod factor perception through a LysM RK complex containing NFR1 and NFR5.  Mutations in both genes lead to non-nodulation (2,3). Yet both genes are duplicated; however, the second copy of GmNFR5 is inactivated by a retrotransposon. Thus the mutant phenotype can be seen as a recessive. In contrast, both copies of GmNFR1 are transcriptionally active. However, alternative splicing occurs in GmNFR1a, and transcript levels of GmNFR1b are low, most likely because of transcript instability caused by a 350 bp deletion inside an intron. Other examples will be presented. 

1) Reid, D.E., Ferguson, B.J., Gresshoff, P.M. (2011) Mol. Plant Microbe Interactions 24: 606-618.

2) Indrasumunar, A., Kereszt, A., Miyagi, M., Nguyen, C.D.T., Li, D.-X., Searle, I., Men, A., Carroll, B.J., Gresshoff, P.M. (2010) Plant Cell Physiol. 51:201-214.

3) Indrasumunar, A., Searle, I., Lin, M.-H., Kereszt, A., Men, A., Carroll, B.J., Gresshoff, P.M. (2011) Plant Journal 65:39-50.