Mutation pressure and natural selection on codon usage in chloroplast genes of two species in Pisum L. (Fabaceae: Faboideae).

This study was attempted to focus on the pattern of codon usage bias (CUB) of chloroplast genes in two species of Pisum viz. P. fulvum and P. sativum and to identify the factors which influence CUB. Bioinformatic tools were used to understand codon usage pattern in the protein-coding sequences of Pisum chloroplast genomes. It was found that GC content was lower than AT content in the genes. Low synonymous codon usage order (SCUO) values of genes indicated low CUB in chloroplast genes of Pisum species. Heatmaps showed positive correlations of GC3 with all the GC and AT ending codons. Neutrality plot analysis revealed that natural selection might have played a prominent role over mutation pressure in sculpturing the CUB of chloroplast genes in these two taxa. Positive correlation between SCUO and mRNA free energy (mFE) suggested that higher energy release by entire mRNA was related to high degree of CUB. Further, highly significant (p < .01) negative correlation was found between parameters in pair i.e. mFE-GC, mFE-GC1, mFE-GC2 and mFE for entire mRNA-GC3. This pointed out that higher GC content might have influenced lesser energy release by mRNA molecules of chloroplast genes.

Transcript free energy positively correlates with codon usage bias in mitochondrial genes of Calypogeia species (Calypogeiaceae, Marchantiophyta).

The present study attempts to focus on the pattern of codon usage bias (CUB) in mitochondrial genes among four species of Calypogeia viz. C. arguta, C. integristipula, C. neogaea and C. suecica along with the factors influencing their CUB as no work was reported yet. The four taxa exhibit noticeable difference in their morphological features, habitat preference and growth forms. To understand the patterns of codon usage in Calypogeia mitochondrial genomes, we used bioinformatic tools to analyze the mitochondrial protein-coding sequences of four Calypogeia. In our current study, the mean nucleobase T was the highest while G was the lowest in all four species. The overall GC content was higher than AT content i.e. genes were AT rich. The CUB was low in mitochondrial genes of C. arguta, C. integristipula, C. neogaea and C. suecica, respectively as revealed from low synonymous codon usage order (SCUO) values. Heat map study revealed that most of the GC and AT ending codons showed positive correlations between codon usage and GC3. From the neutrality plot, the slope of the regression line indicated that natural selection might have played a major role over mutation pressure in shaping the CUB of mitochondrial genes in these four taxa. Highly significant (p < .01) correlation was found between mRNA free energy (mFE) and SCUO for entire mRNA which suggested that the release of higher energy by entire mRNA is associated with higher degree of codon usage bias. Further, highly significant (p < .01) negative correlation of mFE for entire mRNA was found with GC, GC1, GC2 and GC3 in all the four taxa. This indicated that higher GC content might have induced the release of lesser energy by mRNA molecules.

Author Correction: Genomic diversity and macroecology of the crop wild relatives of domesticated pea.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Correction: Genetic structure of wild pea (Pisum sativum subsp. elatius) populations in the northern part of the Fertile Crescent reflects moderate cross-pollination and strong effect of geographic but not environmental distance.

[This corrects the article DOI: 10.1371/journal.pone.0194056.].

Genetic structure of wild pea (Pisum sativum subsp. elatius) populations in the northern part of the Fertile Crescent reflects moderate cross-pollination and strong effect of geographic but not environmental distance.

Knowledge of current genetic diversity and mating systems of crop wild relatives (CWR) in the Fertile Crescent is important in crop genetic improvement, because western agriculture began in the area after the cold-dry period known as Younger Dryas about 12,000 years ago and these species are also wild genepools of the world's most important food crops. Wild pea (Pisum sativum subsp. elatius) is an important source of genetic diversity for further pea crop improvement harbouring traits useful in climate change context. The genetic structure was assessed on 187 individuals of Pisum sativum subsp. elatius from fourteen populations collected in the northern part of the Fertile Crescent using 18,397 genome wide single nucleotide polymorphism DARTseq markers. AMOVA showed that 63% of the allelic variation was distributed between populations and 19% between individuals within populations. Four populations were found to contain admixed individuals. The observed heterozygosity ranged between 0.99 to 6.26% with estimated self-pollination rate between 47 to 90%. Genetic distances of wild pea populations were correlated with geographic but not environmental (climatic) distances and support a mixed mating system with predominant self-pollination. Niche modelling with future climatic projections showed a local decline in habitats suitable for wild pea, making a strong case for further collection and ex situ conservation.

Genomic diversity and macroecology of the crop wild relatives of domesticated pea.

There is growing interest in the conservation and utilization of crop wild relatives (CWR) in international food security policy and research. Legumes play an important role in human health, sustainable food production, global food security, and the resilience of current agricultural systems. Pea belongs to the ancient set of cultivated plants of the Near East domestication center and remains an important crop today. Based on genome-wide analysis, P. fulvum was identified as a well-supported species, while the diversity of wild P. sativum subsp. elatius was structured into 5 partly geographically positioned clusters. We explored the spatial and environmental patterns of two progenitor species of domesticated pea in the Mediterranean Basin and in the Fertile Crescent in relation to the past and current climate. This study revealed that isolation by distance does not explain the genetic structure of P. sativum subsp. elatius in its westward expansion from its center of origin. The genetic diversity of wild pea may be driven by Miocene-Pliocene events, while the phylogenetic diversity centers may reflect Pleisto-Holocene climatic changes. These findings help set research and discussion priorities and provide geographical and ecological information for germplasm-collecting missions, as well as for the preservation of extant diversity in ex-situ collections.