Allelic Diversity of Acetyl Coenzyme A Carboxylase accD/bccp Genes Implicated in Nuclear-Cytoplasmic Conflict in the Wild and Domesticated Pea (Pisum sp.)

Cytoplasmic genomes of Jasminum sambac reveal divergent sub-mitogenomic conformations and a large nuclear chloroplast-derived insertion

BACKGROUND

Jasminum sambac, a widely recognized ornamental plant prized for its aromatic blossoms, exhibits three flora phenotypes: single-petal ("SP"), double-petal ("DP"), and multi-petal ("MP"). The lack of detailed characterization and comparison of J. sambac mitochondrial genomes (mitogenomes) hinders the exploration of the genetic and structural diversity underlying the varying floral phenotypes in jasmine accessions.

RESULTS

Here, we de novo assembled three mitogenomes of typical phenotypes of J. sambac, "SP", "DP", and "MP-hutou" ("HT"), with PacBio reads and the "HT" chloroplast (cp) genome with Illumina reads, and verified them with read mapping and fluorescence in situ hybridization (FISH). The three mitogenomes present divergent sub-genomic conformations, with two, two, and four autonomous circular chromosomes ranging in size from 35.7 kb to 405.3 kb. Each mitogenome contained 58 unique genes. Ribosome binding sites with conserved AAGAAx/AxAAAG motifs were detected upstream of uncanonical start codons TTG, CTG and GTG. The three mitogenomes were similar in genomic content but divergent in structure. The structural variations were mainly attributed to recombination mediated by a large (~ 5 kb) forward repeat pair and several short repeats. The three jasmine cp. genomes showed a well-conserved structure, apart from a 19.9 kb inversion in "HT". We identified a 14.3 kb "HT"-specific insertion on Chr7 of the "HT" nuclear genome, consisting of two 7 kb chloroplast-derived fragments with two intact ndhH and rps15 genes, further validated by polymerase chain reaction (PCR). The well-resolved phylogeny suggests faster mitogenome evolution in J. sambac compared to other Oleaceae species and outlines the mitogenome evolutionary trajectories within Lamiales. All evidence supports that "DP" and "HT" evolved from "SP", with "HT" being the most recent derivative of "DP".

CONCLUSION

The comprehensive characterization of jasmine organelle genomes has added to our knowledge of the structural diversity and evolutionary trajectories behind varying jasmine traits, paving the way for in-depth exploration of mechanisms and targeted genetic research.

Longer Duration of Active Oil Biosynthesis during Seed Development Is Crucial for High Oil Yield-Lessons from Genome-Wide In Silico Mining and RNA-Seq Validation in Sesame

Sesame, one of the ancient oil crops, is an important oilseed due to its nutritionally rich seeds with high protein content. Genomic scale information for sesame has become available in the public databases in recent years. The genes and their families involved in oil biosynthesis in sesame are less studied than in other oilseed crops. Therefore, we retrieved a total of 69 genes and their translated amino acid sequences, associated with gene families linked to the oil biosynthetic pathway. Genome-wide in silico mining helped identify key regulatory genes for oil biosynthesis, though the findings require functional validation. Comparing sequences of the SiSAD (stearoyl-acyl carrier protein (ACP)-desaturase) coding genes with known SADs helped identify two SiSAD family members that may be palmitoyl-ACP-specific. Based on homology with lysophosphatidic acid acyltransferase (LPAAT) sequences, an uncharacterized gene has been identified as SiLPAAT1. Identified key regulatory genes associated with high oil content were also validated using publicly available transcriptome datasets of genotypes contrasting for oil content at different developmental stages. Our study provides evidence that a longer duration of active oil biosynthesis is crucial for high oil accumulation during seed development. This underscores the importance of early onset of oil biosynthesis in developing seeds. Up-regulating, identified key regulatory genes of oil biosynthesis during early onset of seed development, should help increase oil yields.

The genomic signature of wild-to-crop introgression during the domestication of scarlet runner bean (Phaseolus coccineus L.)

The scarlet runner bean (Phaseolus coccineus) is one of the five domesticated Phaseolus species. It is cultivated in small-scale agriculture in the highlands of Mesoamerica for its dry seeds and immature pods, and unlike the other domesticated beans, P. coccineus is an open-pollinated legume. Contrasting with its close relative, the common bean, few studies focusing on its domestication history have been conducted. Demographic bottlenecks associated with domestication might reduce genetic diversity and facilitate the accumulation of deleterious mutations. Conversely, introgression from wild relatives could be a source of variation. Using Genotyping by Sequencing data (79,286 single-nucleotide variants) from 237 cultivated and wild samples, we evaluated the demographic history of traditional varieties from different regions of Mexico and looked for evidence of introgression between sympatric wild and cultivated populations. Traditional varieties have high levels of diversity, even though there is evidence of a severe initial genetic bottleneck followed by a population expansion. Introgression from wild to domesticated populations was detected, which might contribute to the recovery of the genetic variation. Introgression has occurred at different times: constantly in the center of Mexico; recently in the North West; and anciently in the South. Several factors are acting together to increase and maintain genetic diversity in P. coccineus cultivars, such as demographic expansion and introgression. Wild relatives represent a valuable genetic resource and have played a key role in scarlet runner bean evolution via introgression into traditional varieties.

Rapid sequence evolution is associated with genetic incompatibilities in the plastid Clp complex

KEY MESSAGE

Replacing the native clpP1 gene in the Nicotiana plastid genome with homologs from different donor species showed that the extent of genetic incompatibilities depended on the rate of sequence evolution. The plastid caseinolytic protease (Clp) complex plays essential roles in maintaining protein homeostasis and comprises both plastid-encoded and nuclear-encoded subunits. Despite the Clp complex being retained across green plants with highly conserved protein sequences in most species, examples of extremely accelerated amino acid substitution rates have been identified in numerous angiosperms. The causes of these accelerations have been the subject of extensive speculation but still remain unclear. To distinguish among prevailing hypotheses and begin to understand the functional consequences of rapid sequence divergence in Clp subunits, we used plastome transformation to replace the native clpP1 gene in tobacco (Nicotiana tabacum) with counterparts from another angiosperm genus (Silene) that exhibits a wide range in rates of Clp protein sequence evolution. We found that antibiotic-mediated selection could drive a transgenic clpP1 replacement from a slowly evolving donor species (S. latifolia) to homoplasmy but that clpP1 copies from Silene species with accelerated evolutionary rates remained heteroplasmic, meaning that they could not functionally replace the essential tobacco clpP1 gene. These results suggest that observed cases of rapid Clp sequence evolution are a source of epistatic incompatibilities that must be ameliorated by coevolutionary responses between plastid and nuclear subunits.

A photosynthesis operon in the chloroplast genome drives speciation in evening primroses

Genetic incompatibility between the cytoplasm and the nucleus is thought to be a major factor in species formation, but mechanistic understanding of this process is poor. In evening primroses (Oenothera spp.), a model plant for organelle genetics and population biology, hybrid offspring regularly display chloroplast-nuclear incompatibility. This usually manifests in bleached plants, more rarely in hybrid sterility or embryonic lethality. Hence, most of these incompatibilities affect photosynthetic capability, a trait that is under selection in changing environments. Here we show that light-dependent misregulation of the plastid psbB operon, which encodes core subunits of photosystem II and the cytochrome b6f complex, can lead to hybrid incompatibility, and this ultimately drives speciation. This misregulation causes an impaired light acclimation response in incompatible plants. Moreover, as a result of their different chloroplast genotypes, the parental lines differ in photosynthesis performance upon exposure to different light conditions. Significantly, the incompatible chloroplast genome is naturally found in xeric habitats with high light intensities, whereas the compatible one is limited to mesic habitats. Consequently, our data raise the possibility that the hybridization barrier evolved as a result of adaptation to specific climatic conditions.

Validation of a Triplex Quantitative Polymerase Chain Reaction Assay for Detection and Quantification of Traditional Protein Sources, Pisum sativum L. and Glycine max (L.) Merr., in Protein Powder Mixtures

Several botanicals have been traditionally used as protein sources, including the leguminous Pisum sativum L. and Glycine max (L.) Merr. While a rich history exists of cultivating these plants for their whole, protein-rich grain, modern use as powdered supplements present a new challenge in material authentication. The absence of clear morphological identifiers of an intact plant and the existence of long, complex supply chains behoove industry to create quick, reliable analytical tools to identify the botanical source of a protein product (many of which contain multiple sources). The utility of molecular tools for plant-based protein powder authentication is gaining traction, but few validated tools exist. Multiplex quantitative polymerase chain reaction (qPCR) can provide an economical means by which sources can be identified and relative proportions quantified. We followed established guidelines for the design, optimization, and validation of qPCR assay, and developed a triplex qPCR assay that can amplify and quantify pea and soy DNA targets, normalized by a calibrator. The assay was evaluated for analytical specificity, analytical sensitivity, efficiency, precision, dynamic range, repeatability, and reproducibility. We tested the quantitative ability of the assay using pea and soy DNA mixtures, finding exceptional quantitative linearity for both targets - 0.9983 (p < 0.0001) for soy and 0.9915 (p < 0.0001) for pea. Ratios based on mass of protein powder were also tested, resulting in non-linear patterns in data that suggested the requirement of further sample preparation optimization or algorithmic correction. Variation in fragment size within different lots of commercial protein powder samples was also analyzed, revealing low SD among lots. Ultimately, this study demonstrated the utility of qPCR in the context of protein powder mixtures and highlighted key considerations to take into account for commercial implementation.

Legume Genetics and Biology: From Mendel's Pea to Legume Genomics

Legumes have played an important part in cropping systems since the dawn of agriculture, both as human food and as animal feed. The legume family is arguably one of the most abundantly domesticated crop plant families. Their ability to symbiotically fix nitrogen and improve soil fertility has been rewarded since antiquity and makes them a key protein source. The pea was the original model organism used in Mendel’s discovery of the laws of inheritance, making it the foundation of modern plant genetics. This Special Issue provides up-to-date information on legume biology, genetic advances, and the legacy of Mendel.

Genetic and Molecular Genetic Basis of Nuclear-Plastid Incompatibilities

Genetic analysis of nuclear-cytoplasm incompatibilities is not straightforward and requires an elaborated experimental design. A number of species have been genetically studied, but notable advances in genetic mapping of nuclear loci involved in nuclear-plastid incompatibility have been achieved only in wheat and pea. This review focuses on the study of the genetic background underlying nuclear-plastid incompatibilities, including cases where the molecular genetic basis of such incompatibility has been unveiled, such as in tobacco, Oenothera, pea, and wheat.