Role In Evolution Of Organisms Research Articles

The Effects of Gene Duplication Modes on the Evolution of Regulatory Divergence in Wild and Cultivated Soybean.

Regulatory changes include divergence in both cis-elements and trans-factors, which play roles in organismal evolution. Whole genome duplications (WGD) followed by diploidization are a recurrent feature in the evolutionary history of angiosperms. Prior studies have shown that duplicated genes have different evolutionary fates due to variable selection constraints and results in genomic compositions with hallmarks of paleopolyploidy. The recent sequential WGDs and post-WGD evolution in the common ancestor of cultivated soybean (Glycine max) and wild soybean (Glycine soja), together with other models of gene duplication, have resulted in a highly duplicated genome. In this study, we investigated the transcriptional changes in G. soja and G. max. We identified a sizable proportion of interspecific differentially expressed genes (DEGs) and found parental expression level dominance of G. max in their F1 hybrids. By classifying genes into different regulatory divergence types, we found the trans-regulatory changes played a predominant role in transcriptional divergence between wild and cultivated soybean. The same gene ontology (GO) and protein family (Pfam) terms were found to be over-represented in DEGs and genes of cis-only between JY47 and GS, suggesting the substantial contribution of cis-regulatory divergences to the evolution of wild and cultivated soybeans. By further dissecting genes into five different duplication modes, we found genes in different duplication modes tend to accumulate different types of regulatory differences. A relatively higher proportion of cis-only regulatory divergences was detected in singleton, dispersed, proximal, and tandem duplicates than WGD duplicates and genome-wide level, which is in line with the prediction of gene balance hypothesis for the differential fates of duplicated genes post-WGD. The numbers of cis-only and trans-only regulated genes were similar for singletons, whereas there were more genes of trans-only than cis-only in the rest duplication types, especially in WGD in which there were two times more trans-only genes than that in cis-only type. Tandem duplicates showed the highest proportion of trans-only genes probably due to some special features of this class. In summary, our results demonstrate that genes in different duplication modes have different fates in transcriptional evolution underpinned by cis- or trans-regulatory divergences in soybean and likely in other paleopolyploid higher organisms.

Hybridization of Bornean Melastoma: implications for conservation of endemic plants in Southeast Asia

ABSTRACTHybridization has been found as a prevalent circumstance in nature, and it plays important roles in organismal evolution, speciation and even extinction. In this study, we focus on two species of the plant genus Melastoma, which has gone through a rapid species radiation during the last one million years. We successfully detected the hybridization signal between M. malabathricum and M. laevifolium in a suspected hybrid zone in Borneo, Malaysia, by sequencing five nuclear genes and two chloroplast fragments. Most individuals of the suspected hybrids were considered as first generation hybrids, while five individuals corresponded to advanced, early generations of hybrids. Although we did not find any introgression signal between M. malabathricum and M. laevifolium, it is necessary to pay more attention to assess the extinction risk of the species with restricted distribution, here M. laevifolium. This study is the first case of natural hybridization between Melastoma species in Southeast Asia, and more cases are waiting to be found in the field.

Degeneracy of the Genetic Code has Played an Important Role in Evolution of Organisms

Degeneracy of the Genetic Code has Played an Important Role in Evolution of Organisms

Origin of African Physacanthus (Acanthaceae) via Wide Hybridization

Gene flow between closely related species is a frequent phenomenon that is known to play important roles in organismal evolution. Less clear, however, is the importance of hybridization between distant relatives. We present molecular and morphological evidence that support origin of the plant genus Physacanthus via “wide hybridization” between members of two distantly related lineages in the large family Acanthaceae. These two lineages are well characterized by very different morphologies yet, remarkably, Physacanthus shares features of both. Chloroplast sequences from six loci indicate that all three species of Physacanthus contain haplotypes from both lineages, suggesting that heteroplasmy likely predated speciation in the genus. Although heteroplasmy is thought to be unstable and thus transient, multiple haplotypes have been maintained through time in Physacanthus. The most likely scenario to explain these data is that Physacanthus originated via an ancient hybridization event that involved phylogenetically distant parents. This wide hybridization has resulted in the establishment of an independently evolving clade of flowering plants.

Divergence of duplicate genes in exon–intron structure

Gene duplication plays key roles in organismal evolution. Duplicate genes, if they survive, tend to diverge in regulatory and coding regions. Divergences in coding regions, especially those that can change the function of the gene, can be caused by amino acid-altering substitutions and/or alterations in exon-intron structure. Much has been learned about the mode, tempo, and consequences of nucleotide substitutions, yet relatively little is known about structural divergences. In this study, by analyzing 612 pairs of sibling paralogs from seven representative gene families and 300 pairs of one-to-one orthologs from different species, we investigated the occurrence and relative importance of structural divergences during the evolution of duplicate and nonduplicate genes. We found that structural divergences have been very prevalent in duplicate genes and, in many cases, have led to the generation of functionally distinct paralogs. Comparisons of the genomic sequences of these genes further indicated that the differences in exon-intron structure were actually accomplished by three main types of mechanisms (exon/intron gain/loss, exonization/pseudoexonization, and insertion/deletion), each of which contributed differently to structural divergence. Like nucleotide substitutions, insertion/deletion and exonization/pseudoexonization occurred more or less randomly, with the number of observable mutational events per gene pair being largely proportional to evolutionary time. Notably, however, compared with paralogs with similar evolutionary times, orthologs have accumulated significantly fewer structural changes, whereas the amounts of amino acid replacements accumulated did not show clear differences. This finding suggests that structural divergences have played a more important role during the evolution of duplicate than nonduplicate genes.

Patterns of gene duplication in the plant SKP1 gene family in angiosperms: evidence for multiple mechanisms of rapid gene birth

Gene duplication plays important roles in organismal evolution, because duplicate genes provide raw materials for the evolution of mechanisms controlling physiological and/or morphological novelties. Gene duplication can occur via several mechanisms, including segmental duplication, tandem duplication and retroposition. Although segmental and tandem duplications have been found to be important for the expansion of a number of multigene families, the contribution of retroposition is not clear. Here we show that plant SKP1 genes have evolved by multiple duplication events from a single ancestral copy in the most recent common ancestor (MRCA) of eudicots and monocots, resulting in 19 ASK (Arabidopsis SKP1-like) and 28 OSK (Oryza SKP1-like) genes. The estimated birth rates are more than ten times the average rate of gene duplication, and are even higher than that of other rapidly duplicating plant genes, such as type I MADS box genes, R genes, and genes encoding receptor-like kinases. Further analyses suggest that a relatively large proportion of the duplication events may be explained by tandem duplication, but few, if any, are likely to be due to segmental duplication. In addition, by mapping the gain/loss of a specific intron on gene phylogenies, and by searching for the features that characterize retrogenes/retrosequences, we show that retroposition is an important mechanism for expansion of the plant SKP1 gene family. Specifically, we propose that two and three ancient retroposition events occurred in lineages leading to Arabidopsis and rice, respectively, followed by repeated tandem duplications and chromosome rearrangements. Our study represents a thorough investigation showing that retroposition can play an important role in the evolution of a plant gene family whose members do not encode mobile elements.