Evolution: redundancy as an opportunity for innovation

Transcriptome-wide analysis of SAMe superfamily to novelty phosphoethanolamine N-methyltransferase copy in Lonicera japonica

The S-adenosyl-L-methionine-dependent methyltransferase superfamily plays important roles in plant development. The buds of Lonicera japonica are used as Chinese medical material and foods; chinese people began domesticating L. japonica thousands of years ago. Compared to the wild species, L. japonica var. chinensis, L. japonica gives a higher yield of buds, a fact closely related to positive selection over the long cultivation period of the species. Genome duplications, which are always detected in the domestic species, are the source of the multifaceted roles of the functional gene. In this paper, we investigated the evolution of the SAMe genes in L. japonica and L. japonica var. chinensis and further analyzed the roles of the duplicated genes among special groups. The SAMe protein sequences were subdivided into three clusters and several subgroups. The difference in transcriptional levels of the duplicated genes showed that seven SAMe genes could be related to the differences between the wild and the domesticated varieties. The sequence diversity of seven SAMe genes was also analyzed, and the results showed that different gene expression levels between the varieties could not be related to amino acid variation. The transcriptional level of duplicated PEAMT could be regulated through the SAM-SAH cycle.

Cross-talk and information transfer in mammalian and bacterial signaling

In mammalian and bacterial cells simple phosphorylation circuits play an important role in signaling. Bacteria have hundreds of two-component signaling systems that involve phosphotransfer between a receptor and a response regulator. In mammalian cells a similar pathway is the TGF-beta pathway, where extracellular TGF-beta ligands activate cell surface receptors that phosphorylate Smad proteins, which in turn activate many genes. In TGF-beta signaling the multiplicity of ligands begs the question as to whether cells can distinguish signals coming from different ligands, but transduced through a small set of Smads. Here we use information theory with stochastic simulations of networks to address this question. We find that when signals are transduced through only one Smad, the cell cannot distinguish between different levels of the external ligands. Increasing the number of Smads from one to two significantly improves information transmission as well as the ability to discriminate between ligands. Surprisingly, both total information transmitted and the capacity to discriminate between ligands are quite insensitive to high levels of cross-talk between the two Smads. Robustness against cross-talk requires that the average amplitude of the signals are large. We find that smaller systems, as exemplified by some two-component systems in bacteria, are significantly much less robust against cross-talk. For such system sizes phosphotransfer is also less robust against cross-talk than phosphorylation. This suggests that mammalian signal transduction can tolerate a high amount of cross-talk without degrading information content. This may have played a role in the evolution of new functionalities from small mutations in signaling pathways, allowed for the development of cross-regulation and led to increased overall robustness due to redundancy in signaling pathways. On the other hand the lack of cross-regulation observed in many bacterial two-component systems may partly be due to the loss of information content due to cross-talk.