Pattern of diversity in the genomic region near the maize domestication gene tb1

Sweeps in space: leveraging geographic data to identify beneficial alleles in Anopheles gambiae

As organisms adapt to environmental changes, natural selection modifies the frequency of non-neutral alleles. For beneficial mutations, the outcome of this process may be a selective sweep, in which an allele rapidly increases in frequency and perhaps reaches fixation within a population. Selective sweeps have well-studied effects on patterns of local genetic variation in panmictic populations, but much less is known about the dynamics of sweeps in continuous space. In particular, because limited movement across a landscape leads to unique patterns of population structure, spatial dynamics may influence the trajectory of selected mutations. Here, we use forward-in-time, individual-based simulations in continuous space to study the impact of space on beneficial mutations as they sweep through a population. In particular, we show that selection changes the joint distribution of allele frequency and geographic range occupied by a focal allele and demonstrate that this signal can be used to identify selective sweeps. We then leverage this signal to identify in-progress selective sweeps within the malaria vector Anopheles gambiae , a species under strong selection pressure from vector control measures. By considering space, we identify multiple previously undescribed variants with potential phenotypic consequences, including mutations impacting known IR-associated genes and altering protein structure and properties. Our results demonstrate a novel signal for detecting selection in spatial population genetic data that may have implications for genomic surveillance and understanding geographic patterns of genetic variation.

Genome-wide association mapping and genomic prediction analyses reveal the genetic architecture of grain yield and agronomic traits under drought and optimum conditions in maize

BACKGROUND

Drought is a major abiotic stress in sub-Saharan Africa, impacting maize growth and development leading to severe yield loss. Drought tolerance is a complex trait regulated by multiple genes, making direct grain yield selection ineffective. To dissect the genetic architecture of grain yield and flowering traits under drought stress, a genome-wide association study (GWAS) was conducted on a panel of 236 maize lines testcrossed and evaluated under managed drought and optimal growing conditions in multiple environments using seven multi-locus GWAS models (mrMLM, FASTmrMLM, FASTmrEMMA, pLARmEB, pKWmEB, ISIS EM-BLASSO, and FARMCPU) from mrMLM and GAPIT R packages. Genomic prediction with RR-BLUP model was applied on BLUEs across locations under optimum and drought conditions.

RESULTS

A total of 172 stable and reliable quantitative trait nucleotides (QTNs) were identified, of which 77 are associated with GY, AD, SD, ASI, PH, EH, EPO and EPP under drought and 95 are linked to GY, AD, SD, ASI, PH, EH, EPO and EPP under optimal conditions. Among these QTNs, 17 QTNs explained over 10% of the phenotypic variation (R2 ≥ 10%). Furthermore, 43 candidate genes were discovered and annotated. Two major candidate genes, Zm00001eb041070 closely associated with grain yield near peak QTN, qGY_DS1.1 (S1_216149215) and Zm00001eb364110 closely related to anthesis-silking interval near peak QTN, qASI_DS8.2 (S8_167256316) were identified, encoding AP2-EREBP transcription factor 60 and TCP-transcription factor 20, respectively under drought stress. Haplo-pheno analysis identified superior haplotypes for qGY_DS1.1 (S1_216149215) associated with the higher grain yield under drought stress. Genomic prediction revealed moderate to high prediction accuracies under optimum and drought conditions.

CONCLUSION

The lines carrying superior haplotypes can be used as potential donors in improving grain yield under drought stress. Integration of genomic selection with GWAS results leads not only to an increase in the prediction accuracy but also to validate the function of the identified candidate genes as well increase in the accumulation of favorable alleles with minor and major effects in elite breeding lines. This study provides valuable insight into the genetic architecture of grain yield and secondary traits under drought stress.

Analysis of the molecular mechanism endogenous hormone regulating axillary bud development in Pinus yunnanensis

BACKGROUND

P. yunnanensis, a distinctive economic tree species native to Yunnan Province in China, possesses axillary buds that serve as superior material for asexual propagation. However, under natural growth conditions, the differentiation of these axillary buds is notably scarce. In this study, we employed decapitation to stimulate the development of axillary buds in P. yunnanensis. Subsequently, we assessed the phytohormone levels in both axillary and apical buds, and conducted a comprehensive transcriptomic analysis complemented by RT-qPCR validation.

RESULTS

We found that decapitation could effectively promote the releases of the axillary buds in P. yunnanensis. The levels of cytokinin, auxin, gibberellin and abscisic acid in axillary buds were higher than those in apical buds, and the difference in gibberellin levels was the greatest. The transcriptome sequencing results were highly reproducible, and the relative expression levels of the 13 genes screened were highly consistent with the FPKM value trend of transcriptome sequencing. There were 2877 differentially expressed genes (DEGs) between axillary buds and terminal buds, and 18 candidate genes (CGs) involved in axillary bud release were screened out. A total of 1171 DEGs were identified during the analysis of axillary bud growth, and 14 CGs involved in axillary bud growth and development were screened out. GO and KEGG enrichment analysis were performed on the DEGs. Furthermore, combined with the results and discussion, the functions of the candidate genes were analyzed and a possible regulatory network was constructed.

CONCLUSION

The findings and discussions indicated that the development of axillary buds in P. yunnanensis is predominantly governed by cytokinin, gibberellin, strigolactone, and auxin, as well as their biosynthesis and regulatory genes, which are crucial to the development of these buds. This study has, to some extent, bridged the research gap concerning the development of axillary buds in P. yunnanensis and has provided foundational data to support further research into the developmental mechanisms of these buds and the establishment of asexual propagation cutting nurseries.

Comparative population genomics reveals convergent and divergent selection in the apricot-peach-plum-mei complex

The economically significant genus Prunus includes fruit and nut crops that have been domesticated for shared and specific agronomic traits; however, the genomic signals of convergent and divergent selection have not been elucidated. In this study, we aimed to detect genomic signatures of convergent and divergent selection by conducting comparative population genomic analyses of the apricot-peach-plum-mei (APPM) complex, utilizing a haplotype-resolved telomere-to-telomere (T2T) genome assembly and population resequencing data. The haplotype-resolved T2T reference genome for the plum cultivar was assembled through HiFi and Hi-C reads, resulting in two haplotypes 251.25 and 251.29 Mb in size, respectively. Comparative genomics reveals a chromosomal translocation of ~1.17 Mb in the apricot genomes compared with peach, plum, and mei. Notably, the translocation involves the D locus, significantly impacting titratable acidity (TA), pH, and sugar content. Population genetic analysis detected substantial gene flow between plum and apricot, with introgression regions enriched in post-embryonic development and pollen germination processes. Comparative population genetic analyses revealed convergent selection for stress tolerance, flower development, and fruit ripening, along with divergent selection shaping specific crop, such as somatic embryogenesis in plum, pollen germination in mei, and hormone regulation in peach. Notably, selective sweeps on chromosome 7 coincide with a chromosomal collinearity from the comparative genomics, impacting key fruit-softening genes such as PG, regulated by ERF and RMA1H1. Overall, this study provides insights into the genetic diversity, evolutionary history, and domestication of the APPM complex, offering valuable implications for genetic studies and breeding programs of Prunus crops.

Identification of candidate genes associated with less-photosensitive anthocyanin phenotype using an EMS mutant (pind) in eggplant (Solanum melongena L.)

Eggplant (Solanum melongena L.) is a highly nutritious and economically important vegetable crop. However, the fruit peel of eggplant often shows poor coloration owing to low-light intensity during cultivation, especially in the winter. The less-photosensitive varieties produce anthocyanin in low light or even dark conditions, making them valuable breeding materials. Nevertheless, genes responsible for anthocyanin biosynthesis in less-photosensitive eggplant varieties are not characterized. In this study, an EMS mutant, named purple in the dark (pind), was used to identify the key genes responsible for less-photosensitive coloration. Under natural conditions, the peel color and anthocyanin content in pind fruits were similar to that of wildtype '14-345'. The bagged pind fruits were light purple, whereas those of '14-345' were white; and the anthocyanin content in the pind fruit peel was significantly higher than that in '14-345'. Genetic analysis revealed that the less-photosensitive trait was controlled by a single dominant gene. The candidate gene was mapped on chromosome 10 in the region 7.72 Mb to 11.71 Mb. Thirty-five differentially expressed genes, including 12 structural genes, such as CHS, CHI, F3H, DFR, ANS, and UFGT, and three transcription factors MYB113, GL3, and TTG2, were identified in pind using RNA-seq. Four candidate genes EGP21875 (myb domain protein 113), EGP21950 (unknown protein), EGP21953 (CAAX amino-terminal protease family protein), and EGP21961 (CAAX amino-terminal protease family protein) were identified as putative genes associated with less-photosensitive anthocyanin biosynthesis in pind. These findings may clarify the molecular mechanisms underlying less-photosensitive anthocyanin biosynthesis in eggplant.

Large haplotypes highlight a complex age structure within the maize pan-genome

The genomes of maize and other eukaryotes contain stable haplotypes in regions of low recombination. These regions, including centromeres, long heterochromatic blocks, and rDNA arrays, have been difficult to analyze with respect to their diversity and origin. Greatly improved genome assemblies are now available that enable comparative genomics over these and other nongenic spaces. Using 26 complete maize genomes, we developed methods to align intergenic sequences while excluding genes and regulatory regions. The centromere haplotypes (cenhaps) extend for megabases on either side of the functional centromere regions and appear as evolutionary strata, with haplotype divergence/coalescence times dating as far back as 450 thousand years ago (kya). Application of the same methods to other low recombination regions (heterochromatic knobs and rDNA) and all intergenic spaces revealed that deep coalescence times are ubiquitous across the maize pan-genome. Divergence estimates vary over a broad timescale with peaks at ∼16 and 300 kya, reflecting a complex history of gene flow among diverging populations and changes in population size associated with domestication. Cenhaps and other long haplotypes provide vivid displays of this ancient diversity.

The power of classic maize mutants: Driving forward our fundamental understanding of plants

Since Mendel, maize has been a powerhouse of fundamental genetics research. From testing the Mendelian laws of inheritance, to the first genetic and cytogenetic maps, to the use of whole-genome sequencing data for crop improvement, maize is at the forefront of genetics advances. Underpinning much of this revolutionary work are the classic morphological mutants; the "freaks" that stood out in the field to even the untrained eye. Here we review some of these classic developmental mutants and their importance in the history of genetics, as well as their key role in our fundamental understanding of plant development.

How Could the Use of Crop Wild Relatives in Breeding Increase the Adaptation of Crops to Marginal Environments?

Alongside the use of fertilizer and chemical control of weeds, pests, and diseases modern breeding has been very successful in generating cultivars that have increased agricultural production several fold in favorable environments. These typically homogeneous cultivars (either homozygous inbreds or hybrids derived from inbred parents) are bred under optimal field conditions and perform well when there is sufficient water and nutrients. However, such optimal conditions are rare globally; indeed, a large proportion of arable land could be considered marginal for agricultural production. Marginal agricultural land typically has poor fertility and/or shallow soil depth, is subject to soil erosion, and often occurs in semi-arid or saline environments. Moreover, these marginal environments are expected to expand with ongoing climate change and progressive degradation of soil and water resources globally. Crop wild relatives (CWRs), most often used in breeding as sources of biotic resistance, often also possess traits adapting them to marginal environments. Wild progenitors have been selected over the course of their evolutionary history to maintain their fitness under a diverse range of stresses. Conversely, modern breeding for broad adaptation has reduced genetic diversity and increased genetic vulnerability to biotic and abiotic challenges. There is potential to exploit genetic heterogeneity, as opposed to genetic uniformity, in breeding for the utilization of marginal lands. This review discusses the adaptive traits that could improve the performance of cultivars in marginal environments and breeding strategies to deploy them.

Study on Supergenus Rubus L.: Edible, Medicinal, and Phylogenetic Characterization

Rubus L. is one of the most diverse genera belonging to Rosaceae; it consists of more than 700 species with a worldwide distribution. It thus provides an ideal natural "supergenus" for studying the importance of its edible, medicinal, and phylogenetic characteristics for application in our daily lives and fundamental scientific studies. The Rubus genus includes many economically important species, such as blackberry (R. fruticosus L.), red raspberry (R. ideaus L.), black raspberry (R. occidentalis L.), and raspberry (R. chingii Hu), which are widely utilized in the fresh fruit market and the medicinal industry. Although Rubus species have existed in human civilization for hundreds of years, their utilization as fruit and in medicine is still largely inadequate, and many questions on their complex phylogenetic relationships need to be answered. In this review, we briefly summarize the history and progress of studies on Rubus, including its domestication as a source of fresh fruit, its medicinal uses in pharmacology, and its systematic position in the phylogenetic tree. Recent available evidence indicates that (1) thousands of Rubus cultivars were bred via time- and labor-consuming methods from only a few wild species, and new breeding strategies and germplasms were thus limited; (2) many kinds of species in Rubus have been used as medicinal herbs, though only a few species (R. ideaus L., R. chingii Hu, and R. occidentalis L.) have been well studied; (3) the phylogeny of Rubus is very complex, with the main reason for this possibly being the existence of multiple reproductive strategies (apomixis, hybridization, and polyploidization). Our review addresses the utilization of Rubus, summarizing major relevant achievements and proposing core prospects for future application, and thus could serve as a useful roadmap for future elite cultivar breeding and scientific studies.

Genetic Diversity, Structure, and Selective Sweeps in Spinacia turkestanica Associated With the Domestication of Cultivated Spinach

Genotype-by-sequencing (GBS) was used to explore the genetic diversity and structure of Spinacia turkestanica, and the selective sweeps involved in domestication of cultivated spinach, S. oleracea, from S. turkestanica. A total 7,065 single nucleotide polymorphisms (SNPs) generated for 16 Spinacia oleracea and 76 S. turkestanica accessions placed the S. oleracea accessions in one group, Q1, and the 76 S. turkestanica accessions, which originated from Central Asia, in two distinct groups, Q2 and Q3. The Q2 group shared greater genetic identity with the S. oleracea accessions, Q1, than the Q3 S. turkestanica group. Likewise, the S. oleracea Q1 group had a smaller Fst (0.008) with the Q2 group than with the Q3 group (Fst = 0.012), and a greater gene flow (Nm = 30.13) with the Q2 group than with the Q3 group (Nm = 21.83). The Q2 accessions originated primarily from Uzbekistan while the Q3 accessions originated mostly from Tajikistan. The Zarafshan Mountain Range appears to have served as a physical barrier that largely separated members of the Q2 and Q3 groups of S. turkestanica. Accessions with admixtures of Q2 and Q3 were collected primarily from lower elevations at the southern end of the Zarafshan Mountain Range in Uzbekistan. Selective sweep regions identified at 32, 49, and 52 Mb on chromosomes 1, 2, and 3, respectively, appear to have played a vital role in the domestication of S. oleracea as they are correlated with important domestication traits, including day length sensitivity for bolting (flowering). High XP-CLR scores at the 52 Mb genomic region of chromosome three suggest that a selective sweep at this region was responsible for early differentiation of S. turkestanica into two groups in Central Asia.

Gene network simulations provide testable predictions for the molecular domestication syndrome

The domestication of plant species lead to repeatable morphological evolution, often referred to as the phenotypic domestication syndrome. Domestication is also associated with important genomic changes, such as the loss of genetic diversity compared to adequately large wild populations, and modifications of gene expression patterns. Here, we explored theoretically the effect of a domestication-like scenario on the evolution of gene regulatory networks. We ran population genetics simulations in which individuals were featured by their genotype (an interaction matrix encoding a gene regulatory network) and their gene expressions, representing the phenotypic level. Our domestication scenario included a population bottleneck and a selection switch mimicking human-mediated directional and canalizing selection, i.e., change in the optimal gene expression level and selection towards more stable expression across environments. We showed that domestication profoundly alters genetic architectures. Based on four examples of plant domestication scenarios, our simulations predict (i) a drop in neutral allelic diversity, (ii) a change in gene expression variance that depends upon the domestication scenario, (iii) transient maladaptive plasticity, (iv) a deep rewiring of the gene regulatory networks, with a trend towards gain of regulatory interactions, and (v) a global increase in the genetic correlations among gene expressions, with a loss of modularity in the resulting coexpression patterns and in the underlying networks. We provide empirically testable predictions on the differences of genetic architectures between wild and domesticated forms. The characterization of such systematic evolutionary changes in the genetic architecture of traits contributes to define a molecular domestication syndrome.

Fine mapping and candidate gene analysis of the up locus determining fruit orientation in pepper (Capsicum spp.)

The up locus determining fruit orientation was fine-mapped into a region with a physical length of ~169.51 kb on chromosome P12 in pepper. Capana12g000958, encoding a developmentally regulated G protein 2, was proposed as the strongest candidate via sequence comparison and expression analysis. Fruit orientation is an important horticultural and domesticated trait, which is controlled by a single semi-dominant gene (up) in pepper. However, the gene underlying up locus has not yet been identified. In this study, the previously detected major QTL UP12.1 was firstly verified using a backcross population (n = 225) stem from the cross of BB3 (C. annuum) and its wild relative Chiltepin (C. annuum var. glabriusculum) using BB3 as the recurrent parent. Then, a large BC₁F₂ population (n = 1827) was used for recombinant screening to delimit the up locus into an interval with ~ 169.51 kb in length. Sequence comparison and expression analysis suggested that Capana12g000958, encoding a developmentally regulated G protein 2, was the most likely candidate gene for the up locus. There is no difference within the coding sequences of Capana12g000958 between BB3 and Chiltepin, while a SNP in the upstream of Capana12g000958 showed a complete correlation with the fruit orientation among a panel of 40 diverse pepper inbred lines. These findings will form a basis for gene isolation and reveal of genetic mechanism underlying the fruit orientation domestication in pepper.

Candidate genes and signatures of directional selection on fruit quality traits during apple domestication

PREMISE

During plant domestication, traits can be subject to a variety of types of selection, ranging from strong directional selection for traits such as seed or fruit size to diversifying selection for traits like color or flavor. These types of selection interact with other evolutionary processes including genetic bottlenecks and interspecific gene flow to generate different levels of genetic diversity across the genome and at target genes in domesticated lineages, but little is known about the impacts of these processes in perennial fruit crops.

METHODS

We used sequence capture by hybridization to examine patterns of diversity at a suite of candidate domestication and anonymous background genes in domesticated apple (Malus ×domestica) in comparison to its wild relatives Malus sieversii and Malus orientalis.

RESULTS

We found no change in average diversity at these candidate domestication genes across the three species. However, a subset of the genes did exhibit patterns of very high or very low diversity in M. ×domestica compared to its progenitor, M. sieversii. Of the genes with characterized function, the low-diversity genes mainly contributed to fruit quality traits like color and flavor, predicted to be under conscious, directional selection relatively late in the domestication process, while the high-diversity genes included a variety of functions.

CONCLUSIONS

Overall, these results are consistent with predictions based on the likely timing and nature of selection during domestication and open new avenues for understanding genes with high diversity in a perennial crop compared to its wild relatives.

Whole-genome assembly and resequencing reveal genomic imprint and key genes of rapid domestication in narrow-leafed lupin

Shifting from a livestock-based protein diet to a plant-based protein diet has been proposed as an essential requirement to maintain global food sustainability, which requires the increased production of protein-rich crops for direct human consumption. Meanwhile, the lack of sufficient genetic diversity in crop varieties is an increasing concern for sustainable food supplies. Countering this concern requires a clear understanding of the domestication process and dynamics. Narrow-leafed lupin (Lupinus angustifolius L.) has experienced rapid domestication and has become a new legume crop over the past century, with the potential to provide protein-rich seeds. Here, using long-read whole-genome sequencing, we assembled the third-generation reference genome for the narrow-leafed lupin cultivar Tanjil, comprising 20 chromosomes with a total genome size of 615.8 Mb and contig N50 = 5.65 Mb. We characterized the original mutation and putative biological pathway resulting in low seed alkaloid level that initiated the recent domestication of narrow-leafed lupin. We identified a 1133-bp insertion in the cis-regulatory region of a putative gene that may be associated with reduced pod shattering (lentus). A comparative analysis of genomic diversity in cultivars and wild types identified an apparent domestication bottleneck, as precisely predicted by the original model of the bottleneck effect on genetic variability in populations. Our results identify the key domestication genetic loci and provide direct genomic evidence for a domestication bottleneck, and open up the possibility of knowledge-driven de novo domestication of wild plants as an avenue to broaden crop plant diversity to enhance food security and sustainable low-carbon emission agriculture.

Interspecific introgression and natural selection in the evolution of Japanese apricot (Prunus mume)

Domestication and population differentiation in crops involve considerable phenotypic changes. The logs of these evolutionary paths, including natural/artificial selection, can be found in the genomes of the current populations. However, these profiles have been little studied in tree crops, which have specific characters, such as long generation time and clonal propagation, maintaining high levels of heterozygosity. We conducted exon-targeted resequencing of 129 genomes in the genus Prunus, mainly Japanese apricot (Prunus mume), and apricot (Prunus armeniaca), plum (Prunus salicina), and peach (Prunus persica). Based on their genome-wide single-nucleotide polymorphisms merged with published resequencing data of 79 Chinese P. mume cultivars, we inferred complete and ongoing population differentiation in P. mume. Sliding window characterization of the indexes for genetic differentiation identified interspecific fragment introgressions between P. mume and related species (plum and apricot). These regions often exhibited strong selective sweeps formed in the paths of establishment or formation of substructures of P. mume, suggesting that P. mume has frequently imported advantageous genes from other species in the subgenus Prunus as adaptive evolution. These findings shed light on the complicated nature of adaptive evolution in a tree crop that has undergone interspecific exchange of genome fragments with natural/artificial selections.

Genomic inference of complex domestication histories in three Solanaceae species

Domestication is a human-induced selection process that imprints the genomes of domesticated populations over a short evolutionary time scale and that occurs in a given demographic context. Reconstructing historical gene flow, effective population size changes and their timing is therefore of fundamental interest to understand how plant demography and human selection jointly shape genomic divergence during domestication. Yet, the comparison under a single statistical framework of independent domestication histories across different crop species has been little evaluated so far. Thus, it is unclear whether domestication leads to convergent demographic changes that similarly affect crop genomes. To address this question, we used existing and new transcriptome data on three crop species of Solanaceae (eggplant, pepper and tomato), together with their close wild relatives. We fitted twelve demographic models of increasing complexity on the unfolded joint allele frequency spectrum for each wild/crop pair, and we found evidence for both shared and species-specific demographic processes between species. A convergent history of domestication with gene flow was inferred for all three species, along with evidence of strong reduction in the effective population size during the cultivation stage of tomato and pepper. The absence of any reduction in size of the crop in eggplant stands out from the classical view of the domestication process; as does the existence of a "protracted period" of management before cultivation. Our results also suggest divergent management strategies of modern cultivars among species as their current demography substantially differs. Finally, the timing of domestication is species-specific and supported by the few historical records available.

Identification, Association of Natural Variation and Expression Analysis of ZmNAC9 Gene Response to Low Phosphorus in Maize Seedling Stage

Phosphorus (P) is an essential macroelement supporting maize productivity and low-P stress is a limiting factor of maize growth and yield. Improving maize plant tolerance to low P through molecular breeding is an effective alternative to increase crop productivity. In this study, a total of 111 diverse maize inbred lines were used to identify the favorable alleles and nucleotide diversity of candidate ZmNAC9, which plays an important role in response to low P and regulation in root architecture. A significant difference was found under low- and sufficient-P conditions for each of the 22 seedling traits, and a total of 41 polymorphic sites including 32 single nucleotide polymorphisms (SNPs) and 9 insertion and deletions (InDels) were detected in ZmNAC9 among 111 inbred lines. Among the 41 polymorphic studied sites, a total of 39 polymorphic sites were associated with 20 traits except for the dry weight of shoots and forks, of which six sites were highly significantly associated with a diverse number of low-P tolerant root trait index values by using a mixed linear model (MLM) at −log10 P = 3.61. In addition, 29 polymorphic sites under P-sufficient and 32 polymorphic sites under P-deficient conditions were significantly associated with a diverse number of seedling traits, of which five polymorphic sites (position S327, S513, S514, S520, and S827) were strongly significantly associated with multiple seedling traits under low-P and normal-P conditions. Among highly significant sites, most of the sites were associated with root traits under low-P, normal-P, and low-P trait index values. Linkage disequilibrium (LD) was strong at (r2 > 1.0) in 111 inbred lines. Furthermore, the effect of five significant sites was verified for haplotypes in 111 lines and the favorable allele S520 showed a positive effect on the dry weight of roots under the low-P condition. Furthermore, the expression pattern confirmed that ZmNAC9 was highly induced by low P in the roots of the P-tolerant 178 inbred line. Moreover, the subcellular localization of ZmNAC9 encoded by protein was located in the cytoplasm and nucleus. Haplotypes carrying more favorable alleles exhibited superior effects on phenotypic variation and could be helpful in developing molecular markers in maize molecular breeding programs. Taken together, the finding of this study might lead to further functions of ZmNAC9 and genes that might be involved in responses to low-P stress in maize.

Global Role of Crop Genomics in the Face of Climate Change

The development of climate change resilient crops is necessary if we are to meet the challenge of feeding the growing world's population. We must be able to increase food production despite the projected decrease in arable land and unpredictable environmental conditions. This review summarizes the technological and conceptual advances that have the potential to transform plant breeding, help overcome the challenges of climate change, and initiate the next plant breeding revolution. Recent developments in genomics in combination with high-throughput and precision phenotyping facilitate the identification of genes controlling critical agronomic traits. The discovery of these genes can now be paired with genome editing techniques to rapidly develop climate change resilient crops, including plants with better biotic and abiotic stress tolerance and enhanced nutritional value. Utilizing the genetic potential of crop wild relatives (CWRs) enables the domestication of new species and the generation of synthetic polyploids. The high-quality crop plant genome assemblies and annotations provide new, exciting research targets, including long non-coding RNAs (lncRNAs) and cis-regulatory regions. Metagenomic studies give insights into plant-microbiome interactions and guide selection of optimal soils for plant cultivation. Together, all these advances will allow breeders to produce improved, resilient crops in relatively short timeframes meeting the demands of the growing population and changing climate.

The genetic architecture of the maize progenitor, teosinte, and how it was altered during maize domestication

The genetics of domestication has been extensively studied ever since the rediscovery of Mendel's law of inheritance and much has been learned about the genetic control of trait differences between crops and their ancestors. Here, we ask how domestication has altered genetic architecture by comparing the genetic architecture of 18 domestication traits in maize and its ancestor teosinte using matched populations. We observed a strongly reduced number of QTL for domestication traits in maize relative to teosinte, which is consistent with the previously reported depletion of additive variance by selection during domestication. We also observed more dominance in maize than teosinte, likely a consequence of selective removal of additive variants. We observed that large effect QTL have low minor allele frequency (MAF) in both maize and teosinte. Regions of the genome that are strongly differentiated between teosinte and maize (high FST) explain less quantitative variation in maize than teosinte, suggesting that, in these regions, allelic variants were brought to (or near) fixation during domestication. We also observed that genomic regions of high recombination explain a disproportionately large proportion of heritable variance both before and after domestication. Finally, we observed that about 75% of the additive variance in both teosinte and maize is "missing" in the sense that it cannot be ascribed to detectable QTL and only 25% of variance maps to specific QTL. This latter result suggests that morphological evolution during domestication is largely attributable to very large numbers of QTL of very small effect.

Selective sweeps on novel and introgressed variation shape mimicry loci in a butterfly adaptive radiation

Natural selection leaves distinct signatures in the genome that can reveal the targets and history of adaptive evolution. By analysing high-coverage genome sequence data from 4 major colour pattern loci sampled from nearly 600 individuals in 53 populations, we show pervasive selection on wing patterns in the Heliconius adaptive radiation. The strongest signatures correspond to loci with the greatest phenotypic effects, consistent with visual selection by predators, and are found in colour patterns with geographically restricted distributions. These recent sweeps are similar between co-mimics and indicate colour pattern turn-over events despite strong stabilising selection. Using simulations, we compare sweep signatures expected under classic hard sweeps with those resulting from adaptive introgression, an important aspect of mimicry evolution in Heliconius butterflies. Simulated recipient populations show a distinct 'volcano' pattern with peaks of increased genetic diversity around the selected target, characteristic of sweeps of introgressed variation and consistent with diversity patterns found in some populations. Our genomic data reveal a surprisingly dynamic history of colour pattern selection and co-evolution in this adaptive radiation.

Integrating the dynamics of yield traits in rice in response to environmental changes

Reductions in crop yields as a consequence of global climate change threaten worldwide food security. It is therefore imperative to develop high-yielding crop plants that show sustainable production under stress conditions. In order to achieve this aim through breeding or genetic engineering, it is crucial to have a complete and comprehensive understanding of the molecular basis of plant architecture and the regulation of its sub-components that contribute to yield under stress. Rice is one of the most widely consumed crops and is adversely affected by abiotic stresses such as drought and salinity. Using it as a model system, in this review we present a summary of our current knowledge of the physiological and molecular mechanisms that determine yield traits in rice under optimal growth conditions and under conditions of environmental stress. Based on physiological functioning, we also consider the best possible combination of genes that may improve grain yield under optimal as well as environmentally stressed conditions. The principles that we present here for rice will also be useful for similar studies in other grain crops.

Identification of Selective Sweeps in the Domesticated Table and Wine Grape (Vitis vinifera L.)

Grapevine (Vitis vinifera) is one of the most important fruit species in the Classical Mediterranean world. It is thought to have been domesticated 6,000-8,000 years ago in the Near East. However, the domestication of its wild relative into wine grapes or table grapes remains largely unknown. In this study, we analyzed 30 table grapes, 30 wine grapes, 30 dual-purpose grape accessions, as well as 30 wild relatives (Vitis vinifera ssp. sylvestris). The phenotypic comparison showed striking differences in berry weight, acidity and the content of aroma. Based on a total of 7,522,958 single-nucleotide polymorphisms, we identified several significant selective sweep regions for table and wine grapes. Besides the well-known sex-determination locus on chromosome 2, the other four highest signals shared by table and wine grapes could not be linked to the known QTLs. The identification of these genomic regions under selection sweep may reveal agronomically important traits that have been selected during grape domestication. This information not only sheds light on the mechanisms of adaptions and diversification, but also guide the genetic improvement in breeding programs.

Unraveling cis and trans regulatory evolution during cotton domestication

Cis and trans regulatory divergence underlies phenotypic and evolutionary diversification. Relatively little is understood about the complexity of regulatory evolution accompanying crop domestication, particularly for polyploid plants. Here, we compare the fiber transcriptomes between wild and domesticated cotton (Gossypium hirsutum) and their reciprocal F1 hybrids, revealing genome-wide (~15%) and often compensatory cis and trans regulatory changes under divergence and domestication. The high level of trans evolution (54%-64%) observed is likely enabled by genomic redundancy following polyploidy. Our results reveal that regulatory variation is significantly associated with sequence evolution, inheritance of parental expression patterns, co-expression gene network properties, and genomic loci responsible for domestication traits. With respect to regulatory evolution, the two subgenomes of allotetraploid cotton are often uncoupled. Overall, our work underscores the complexity of regulatory evolution during fiber domestication and may facilitate new approaches for improving cotton and other polyploid plants.

MaizeSNPDB: A comprehensive database for efficient retrieve and analysis of SNPs among 1210 maize lines

With the rapid decreasing of sequencing cost, large volume of genotype data has been generated in many organisms based on high-throughput sequencing, which was utilized in various fields of biological studies in the post-genome era. The raw sequencing data were usually deposited in the NCBI SRA database. Construction of the database to store and analyze the processed genotype data is an essential step for the utilization of the genotype data by the community. Up to now, a comprehensive genotype database is still missing from maize, which is an important crop of the world. We report the construction of the MaizeSNPDB database using genotype data of 1210 maize line across 35,370,939 SNP sites refined from a large set of genomic variations reported by the maize HapMap 3 project. We further implemented several genetic analysis programs as graphical interfaces in the MaizeSNPDB database. SNPs in user-specified genomic regions could be easily extracted and analyzed in MaizeSNPDB. The whole dataset and code of MaizeSNPDB is available at https://github.com/venyao/MaizeSNPDB. MaizeSNPDB is deployed at http://150.109.59.144:3838/MaizeSNPDB/ for online use. The MaizeSNPDB database is of great value to future maize functional genomic studies, which can also facilitate marker-assisted breeding in maize.

Bi-directional Selection in Upland Rice Leads to Its Adaptive Differentiation from Lowland Rice in Drought Resistance and Productivity

Drought resistance is required in rice breeding to address the challenge of frequent droughts. However, the evolutionary mechanism of rice drought resistance is not fully understood. We investigated the genetic differentiation between upland and lowland rice domesticated in agro-ecosystems with contrasting water-soil conditions using genome-wide SNPs. We estimated morphological differences among upland and lowland rice in drought resistance and productivity through common garden experiments. Upland rice had better drought resistance but poorer productivity. The negative correlations between traits of drought resistance and productivity are attributed to the underlying genetic trade-offs through tight linkages (e.g., DCA1 and OsCesA7) or pleiotropic effects (e.g., LAX1). The genetic trade-offs are common and greatly shape the evolution of drought resistance in upland rice. In genomic regions associated with both productivity and drought resistance, signs of balancing selection were detected in upland rice, while signs of directional selection were detected in lowland rice, potentially contributing to their adaptive differentiation. Signs of balancing selection in upland rice resulted from bi-directional selection during its domestication in drought-prone upland agro-ecosystems. Using genome-wide association analysis, we identified several valuable quantitative trait loci associated with drought resistance, for which highly differentiated genes should be considered candidates. Bi-directional selection breaking tight linkages by accumulating recombination events would be applicable in breeding water-saving and drought-resistance rice.

GmBRC1 is a Candidate Gene for Branching in Soybean (Glycine max (L.) Merrill)

Branch number is one of the main factors affecting the yield of soybean (Glycine max (L.)). In this study, we conducted a genome-wide association study combined with linkage analysis for the identification of a candidate gene controlling soybean branching. Five quantitative trait nucleotides (QTNs) were associated with branch numbers in a soybean core collection. Among these QTNs, a linkage disequilibrium (LD) block qtnBR6-1 spanning 20 genes was found to overlap a previously identified major quantitative trait locus qBR6-1. To validate and narrow down qtnBR6-1, we developed a set of near-isogenic lines (NILs) harboring high-branching (HB) and low-branching (LB) alleles of qBR6-1, with 99.96% isogenicity and different branch numbers. A cluster of single nucleotide polymorphisms (SNPs) segregating between NIL-HB and NIL-LB was located within the qtnBR6-1 LD block. Among the five genes showing differential expression between NIL-HB and NIL-LB, BRANCHED1 (BRC1; Glyma.06G210600) was down-regulated in the shoot apex of NIL-HB, and one missense mutation and two SNPs upstream of BRC1 were associated with branch numbers in 59 additional soybean accessions. BRC1 encodes TEOSINTE-BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS 1 and 2 transcription factor and functions as a regulatory repressor of branching. On the basis of these results, we propose BRC1 as a candidate gene for branching in soybean.

GmBRC1 is a Candidate Gene for Branching in Soybean (Glycine max (L.) Merrill)

Branch number is one of the main factors affecting the yield of soybean (Glycine max (L.)). In this study, we conducted a genome-wide association study combined with linkage analysis for the identification of a candidate gene controlling soybean branching. Five quantitative trait nucleotides (QTNs) were associated with branch numbers in a soybean core collection. Among these QTNs, a linkage disequilibrium (LD) block qtnBR6-1 spanning 20 genes was found to overlap a previously identified major quantitative trait locus qBR6-1. To validate and narrow down qtnBR6-1, we developed a set of near-isogenic lines (NILs) harboring high-branching (HB) and low-branching (LB) alleles of qBR6-1, with 99.96% isogenicity and different branch numbers. A cluster of single nucleotide polymorphisms (SNPs) segregating between NIL-HB and NIL-LB was located within the qtnBR6-1 LD block. Among the five genes showing differential expression between NIL-HB and NIL-LB, BRANCHED1 (BRC1; Glyma.06G210600) was down-regulated in the shoot apex of NIL-HB, and one missense mutation and two SNPs upstream of BRC1 were associated with branch numbers in 59 additional soybean accessions. BRC1 encodes TEOSINTE-BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS 1 and 2 transcription factor and functions as a regulatory repressor of branching. On the basis of these results, we propose BRC1 as a candidate gene for branching in soybean.

Deletions linked to PROG1 gene participate in plant architecture domestication in Asian and African rice

Improving the yield by modifying plant architecture was a key step during crop domestication. Here, we show that a 110-kb deletion on the short arm of chromosome 7 in Asian cultivated rice (Oryza sativa), which is closely linked to the previously identified PROSTRATE GROWTH 1 (PROG1) gene, harbors a tandem repeat of seven zinc-finger genes. Three of these genes regulate the plant architecture, suggesting that the deletion also promoted the critical transition from the prostrate growth and low yield of wild rice (O. rufipogon) to the erect growth and high yield of Asian cultivated rice. We refer to this locus as RICE PLANT ARCHITECTURE DOMESTICATION (RPAD). Further, a similar but independent 113-kb deletion is detected at the RPAD locus in African cultivated rice. These results indicate that the deletions, eliminating a tandem repeat of zinc-finger genes, may have been involved in the parallel domestication of plant architecture in Asian and African rice.

Plant architecture transition is one of the great consequences during rice domestication. Here, the authors find that chromosomal deletions linked to the previously known PROG1 gene also participate in plant architecture domestication in both Asian and African cultivated rice.

Molecular cloning and sequence variance analysis of the TEOSINTE BRANCHED1 (TB1) gene in bermudagrass [Cynodon dactylon (L.) Pers]

TEOSINTE BRANCHED1 (TB1) encodes a TEOSINTE BRANCHED1, CYCLOIDEA, and PROLIFERATING CELL FACTOR (TCP) transcription factor that represses axillary bud outgrowth and lateral branch formation in plants. Previous studies have elucidated the essential tillering regulatory roles of TB1 in many grasses, including maize and rice; however, the functions of TB1 in turf grasses remain unclear. In this study, we cloned the CdTB1 gene from bermudagrass, an important turfgrass species, and characterized the transactivation function of the CdTB1 protein. Sequencing the CdTB1 gene locus in a mini-core germplasm collection of Chinese bermudagrasses led to the successful identification of 66 SNP and 2 indel mutations in the protein-coding region as well as 28 SNP and 11 indel mutations in the promoter region. Interestingly, mutations in the C-terminal transactivation domain of the CdTB1 protein had no significant influence on the transactivation activity, whereas a novel 335-bp insertion mutation located in the promoter region could significantly increase the expression of the CdTB1 gene. Furthermore, wild accessions of bermudagrass harboring the novel insertion mutation were found to have significantly reduced tillers compared with other accessions, suggesting a negative correlation between the mutation and tillering. The results of this study not only expanded our knowledge of TB1 gene expression regulation but also provided possible molecular markers to breed cultivars of turf and forage grasses with specific architectural features.

Genetic diversity and evolution of reduced sulfur storage during domestication of maize

The domestication of maize has spanned a period of over 9000 years, during which time its wild relative teosinte underwent natural and artificial selection. We hypothesize that environmental conditions could have played a major role in this process. One factor of environmental variation is soil composition, which includes sulfur availability. Sulfur is reduced during photosynthesis and is used to synthesize cysteine and methionine, which drive the accumulation of δ10 (Zm00001d045937), δ18 (Zm00001d037436), β15 (Zm00001d035760), γ16 (Zm00001d005793), γ27 (Zm00001d020592), and γ50 (Zm00001d020591) zeins, representing the zein2 fraction (z2) of storage proteins in maize seeds. In this study, polymorphisms and haplotypes were detected based on six z2 genes in 60 maize and teosintes lines. Haplotypes were unevenly distributed, and abundant genetic diversity was found in teosintes. Polymorphism was highest in z2δ18, whereas for z2β15 single nucleotide polymorphism (SNP) density and insertion/deletion (indel) abundance were the lowest, indicating differential roles in seed evolution. Indels showed a clustered distribution, and most of these derived from teosintes. The indels not only led to tandem repeat polymorphisms, but also to frameshift mutations, which could also be used as null variants. In addition, neutral evolutionary tests, phylogenetic analyses, and population structures indicated that z2δ10 and z2γ50 had undergone natural selection. Indeed, a natural selection imprint could also be found with z2γ27 and z2γ16, whereas z2δ18 and z2β15 tended to be under neutral evolution. These results suggested that genetic diversity and evolution of a subset of sulfur-rich zeins could be under environmental adaptation during maize domestication.

Largely unlinked gene sets targeted by selection for domestication syndrome phenotypes in maize and sorghum

The domestication of diverse grain crops from wild grasses was a result of artificial selection for a suite of overlapping traits producing changes referred to in aggregate as 'domestication syndrome'. Parallel phenotypic change can be accomplished by either selection on orthologous genes or selection on non-orthologous genes with parallel phenotypic effects. To determine how often artificial selection for domestication traits in the grasses targeted orthologous genes, we employed resequencing data from wild and domesticated accessions of Zea (maize) and Sorghum (sorghum). Many 'classic' domestication genes identified through quantitative trait locus mapping in populations resulting from wild/domesticated crosses indeed show signatures of parallel selection in both maize and sorghum. However, the overall number of genes showing signatures of parallel selection in both species is not significantly different from that expected by chance. This suggests that while a small number of genes will extremely large phenotypic effects have been targeted repeatedly by artificial selection during domestication, the optimization part of domestication targeted small and largely non-overlapping subsets of all possible genes which could produce equivalent phenotypic alterations.

Evolutionary history of the NAM-B1 gene in wild and domesticated tetraploid wheat

BACKGROUND

The NAM-B1 gene in wheat has for almost three decades been extensively studied and utilized in breeding programs because of its significant impact on grain protein and mineral content and pleiotropic effects on senescence rate and grain size. First detected in wild emmer wheat, the wild-type allele of the gene has been introgressed into durum and bread wheat. Later studies have, however, also found the presence of the wild-type allele in some domesticated subspecies. In this study we trace the evolutionary history of the NAM-B1 in tetraploid wheat species and evaluate it as a putative domestication gene.

RESULTS

Genotyping of wild and landrace tetraploid accessions showed presence of only null alleles in durum. Domesticated emmer wheats contained both null alleles and the wild-type allele while wild emmers, with one exception, only carried the wild-type allele. One of the null alleles consists of a deletion that covers several 100 kb. The other null-allele, a one-basepair frame-shift insertion, likely arose among wild emmer. This allele was the target of a selective sweep, extending over several 100 kb.

CONCLUSIONS

The NAM-B1 gene fulfils some criteria for being a domestication gene by encoding a trait of domestication relevance (seed size) and is here shown to have been under positive selection. The presence of both wild-type and null alleles in domesticated emmer does, however, suggest the gene to be a diversification gene in this species. Further studies of genotype-environment interactions are needed to find out under what conditions selection on different NAM-B1 alleles have been beneficial.

Combined Haplotypes of CaSR Gene Sequence Variants and Their Associations with Growth Traits in Cattle

The calcium-sensing receptor (CaSR) is a Class C G-protein coupled receptor that regulates food intake and assimilation. However, studies on the relationship between CaSR gene and growth traits in cattle are deficient. The aim of this study was to examine the association of the CaSR polymorphism with growth traits in cattle breeds. Four novel single nucleotide polymorphisms (SNPs) and one previously reported SNP (NC_007299.5: g.67630865T>C, 67638409G>C, 67660395G>C, 67661546C>G, and 67661892A>C) were identified in the bovine CaSR gene using DNA sequencing and PCR-SSCP methods in 520 individuals from three representative breeds. The three SNP P4_2, P7_1, and P7_4 in LX, QC, and JX cattle populations belonged to intermediate genetic diversity (0.25 < PIC < 0.5). In addition, we evaluated the haplotype frequency and linkage disequilibrium coefficient of five sequence variants in the three cattle breeds. LD and haplotype structure of CaSR were different between breeds. LD analysis showed that the P4_2 and P7_4 loci were in complete LD in JX cattle population (r2 = 0.99 and D' = 1). Only 11 haplotypes were listed except for those with a frequency of <0.03. Hap1 (-TGGGC-) had the highest haplotype frequencies in LX (27.30%), Hap6(-TGGCC-) had the highest haplotype frequencies in QC (21.70%) and JX (32.30%). Association analysis indicated that P2, P4_2, and P7_4 loci were all significantly associated with growth traits and combined genotype TTGCGC was highly significantly associated with Chest circumference and body weight than the other genotype in JX cattle population. The results of this study suggest that the CaSR gene possibly is a strong candidate gene that affects growth traits in the Chinese cattle breeding program.

Non-random transmission of parental alleles into crop-wild and crop-weed hybrid lineages separated by a transgene and neutral identifiers in rice

It is essential to assess environmental impact of transgene flow from genetically engineered crops to their wild or weedy relatives before commercialization. Measuring comparative trials of fitness in the transgene-flow-resulted hybrids plays the key role in the assessment, where the segregated isogenic hybrid lineages/subpopulations with or without a transgene of the same genomic background are involved. Here, we report substantial genomic differentiation between transgene-present and -absent lineages (F₂-F₃) divided by a glyphosate-resistance transgene from a crop-wild/weed hybrid population in rice. We further confirmed that such differentiation is attributed to increased frequencies of crop-parent alleles in transgenic hybrid lineages at multiple loci across the genome, as estimated by SSR (simple sequence repeat) markers. Such preferential transmission of parental alleles was also found in equally divided crop-wild/weed hybrid lineages with or without a particular neutral SSR identifier. We conclude that selecting either a transgene or neutral marker as an identifier to create hybrid lineages will result in different genomic background of the lineages due to non-random transmission of parental alleles. Non-random allele transmission may misrepresent the outcomes of fitness effects. We therefore propose seeking other means to evaluate fitness effects of transgenes for assessing environmental impact caused by crop-to-wild/weed gene flow.

Signatures of soft sweeps across the Dt1 locus underlying determinate growth habit in soya bean [Glycine max (L.) Merr.]

Determinate growth habit is an agronomically important trait associated with domestication in soya bean. Previous studies have demonstrated that the emergence of determinacy is correlated with artificial selection on four nonsynonymous mutations in the Dt1 gene. To better understand the signatures of the soft sweeps across the Dt1 locus and track the origins of the determinate alleles, we examined patterns of nucleotide variation in Dt1 and the surrounding genomic region of approximately 800 kb. Four local, asymmetrical hard sweeps on four determinate alleles, sized approximately 660, 120, 220 and 150 kb, were identified, which constitute the soft sweeps for the adaptation. These variable-sized sweeps substantially reflected the strength and timing of selection and indicated that the selection on the alleles had been completed rapidly within half a century. Statistics of EHH, iHS, H12 and H2/H1 based on haplotype data had the power to detect the soft sweeps, revealing distinct signatures of extensive long-range LD and haplotype homozygosity, and multiple frequent adaptive haplotypes. A haplotype network constructed for Dt1 and a phylogenetic tree based on its extended haplotype block implied independent sources of the adaptive alleles through de novo mutations or rare standing variation in quick succession during the selective phase, strongly supporting multiple origins of the determinacy. We propose that the adaptation of soya bean determinacy is guided by a model of soft sweeps and that this model might be indispensable during crop domestication or evolution.

Patterns of Genetic Structure and Linkage Disequilibrium in a Large Collection of Pea Germplasm

Pea (Pisum sativum, L.) is a major pulse crop used both for animal and human alimentation. Owing to its association with nitrogen-fixing bacteria, it is also a valuable component for low-input cropping systems. To evaluate the genetic diversity and the scale of linkage disequilibrium (LD) decay in pea, we genotyped a collection of 917 accessions, gathering elite cultivars, landraces, and wild relatives using an array of ∼13,000 single nucleotide polymorphisms (SNP). Genetic diversity is broadly distributed across three groups corresponding to wild/landraces peas, winter types, and spring types. At a finer subdivision level, genetic groups relate to local breeding programs and type usage. LD decreases steeply as genetic distance increases. When considering subsets of the data, LD values can be higher, even if the steep decay remains. We looked for genomic regions exhibiting high level of differentiation between wild/landraces, winter, and spring pea, respectively. Two regions on linkage groups 5 and 6 containing 33 SNPs exhibit stronger differentiation between winter and spring peas than would be expected under neutrality. Interestingly, QTL for resistance to cold acclimation and frost resistance have been identified previously in the same regions.

Domestication rewired gene expression and nucleotide diversity patterns in tomato

Plant domestication has led to considerable phenotypic modifications from wild species to modern varieties. However, although changes in key traits have been well documented, less is known about the underlying molecular mechanisms, such as the reduction of molecular diversity or global gene co-expression patterns. In this study, we used a combination of gene expression and population genetics in wild and crop tomato to decipher the footprints of domestication. We found a set of 1729 differentially expressed genes (DEG) between the two genetic groups, belonging to 17 clusters of co-expressed DEG, suggesting that domestication affected not only individual genes but also regulatory networks. Five co-expression clusters were enriched in functional terms involving carbohydrate metabolism or epigenetic regulation of gene expression. We detected differences in nucleotide diversity between the crop and wild groups specific to DEG. Our study provides an extensive profiling of the rewiring of gene co-expression induced by the domestication syndrome in one of the main crop species.

Functional Conservation and Divergence among Homoeologs of TaSPL20 and TaSPL21, Two SBP-Box Genes Governing Yield-Related Traits in Hexaploid Wheat

Maintaining high and stable yields has become an increasing challenge in wheat breeding due to climate change. Although Squamosa-promoter binding protein (SBP)-box genes have important roles in plant development, very little is known about the actual biological functions of wheat SBP-box family members. Here, we dissect the functional conservation, divergence, and exploitation of homoeologs of two paralogous TaSPL wheat loci during domestication and breeding. TaSPL20 and TaSPL21 were highly expressed in the lemma and palea. Ectopic expressions of TaSPL20/21 in rice exhibited similar functions in terms of promoting panicle branching but had different functions during seed development. We characterized all six TaSPL20/21 genes located across the three homoeologous (A, B, and D) genomes. According to the functional analysis of naturally occurring variants in 20 environments, four favorable haplotypes were identified. Together, they reduced plant height by up to 27.5%, and TaSPL21-6D-HapII increased 1000-grain weight by 9.73%. Our study suggests that TaSPL20 and TaSPL21 homoeologs underwent diversification in function with each evolving its own distinctive characteristics. During domestication and breeding of wheat in China, favorable haplotypes of each set were selected and exploited to varying degrees due to their large effects on plant height and 1000-grain weight.

Evolutionary trajectories of duplicated FT homologues and their roles in soybean domestication

To clarify the molecular bases of flowering time evolution in crop domestication, here we investigate the evolutionary fates of a set of four recently duplicated genes in soybean: FT2a, FT2b, FT2c and FT2d that are homologues of the floral inducer FLOWERING LOCUS T (FT). While FT2a maintained the flowering inducer function, other genes went through contrasting evolutionary paths. FT2b evolved attenuated expression potentially associated with a transposon insertion in the upstream intergenic region, while FT2c and FT2d obtained a transposon insertion and structural rearrangement, respectively. In contrast to FT2b and FT2d whose mutational events occurred before the separation of G. max and G. soja, the evolution of FT2c is a G. max lineage specific event. The FT2c allele carrying a transposon insertion is nearly fixed in soybean landraces and differentiates domesticated soybean from wild soybean, indicating that this allele spread at the early stage of soybean domestication. The domesticated allele causes later flowering than the wild allele under short day and exhibits a signature of selection. These findings suggest that FT2c may have underpinned the evolution of photoperiodic flowering regulation in soybean domestication and highlight the evolutionary dynamics of this agronomically important gene family.

Fast diffusion of domesticated maize to temperate zones

Adaptation to a temperate climate was a prerequisite for the spread of maize across a broad geographical range. To explicitly explore the demographic process underlying maize adaptation, we used a diffusion-based method to model the differentiation between temperate and tropical populations using the Non-Stiff Stalk group as a proxy for temperate maize. Based on multiple sequential Markovian coalescent approaches, we estimate that tropical and temperate maize diverged approximately 3'000 to 5'000 years ago and the population size shrank after the split. Using composite likelihood approaches, we identified a distinct tropical-temperate divergence event initiated 4'958 years ago (95% confidence interval (CI): 4'877-5'039) from an ancestral population whose effective size was 24,162 (95% CI: 23,914-24,409). We found that continuous gene flow between tropical and temperate maize accompanied the differentiation of temperate maize. Long identical-by-descent tracts shared by tropical and temperate inbred lines have been identified, which might be the result of gene flow between tropical and temperate maize or artificial selection during domestication and crop improvement. Understanding the demographic history of maize diffusion not only provides evidence for population dynamics of maize, but will also assist the identification of regions under selection and the genetic basis of complex traits of agronomic importance.

Soybean domestication: the origin, genetic architecture and molecular bases

Domestication provides an important model for the study of evolution, and information learned from domestication research aids in the continued improvement of crop species. Recent progress in de novo assembly and whole-genome resequencing of wild and cultivated soybean genomes, in addition to new archeological discoveries, sheds light on the origin of this important crop and provides a clearer view on the modes of artificial selection that drove soybean domestication and diversification. This novel genomic information enables the search for polymorphisms that underlie variation in agronomic traits and highlights genes that exhibit a signature of selection, leading to the identification of a number of candidate genes that may have played important roles in soybean domestication, diversification and improvement. These discoveries provide a novel point of comparison on the evolutionary bases of important agronomic traits among different crop species.

What can genome-wide association studies tell us about the evolutionary forces maintaining genetic variation for quantitative traits?

Contents 21 I. 21 II. 22 III. 24 IV. 25 V. 29 30 References 30 SUMMARY: Understanding the evolutionary forces that shape genetic variation within species has long been a goal of evolutionary biology. Integrating data for the genetic architecture of traits from genome-wide association mapping studies (GWAS) along with the development of new population genetic methods for identifying selection in sequence data may allow us to evaluate the roles of mutation-selection balance and balancing selection in shaping genetic variation at various scales. Here, we review the theoretical predictions for genetic architecture and additional signals of selection on genomic sequence for the loci that affect traits. Next, we review how plant GWAS have tested for the signatures of various selective scenarios. Limited evidence to date suggests that within-population variation is maintained primarily by mutation-selection balance while variation across the landscape is the result of local adaptation. However, there are a number of inherent biases in these interpretations. We highlight these challenges and suggest ways forward to further understanding of the maintenance of variation.

Back into the wild-Apply untapped genetic diversity of wild relatives for crop improvement

Deleterious effects of climate change and human activities, as well as diverse environmental stresses, present critical challenges to food production and the maintenance of natural diversity. These challenges may be met by the development of novel crop varieties with increased biotic or abiotic resistance that enables them to thrive in marginal lands. However, considering the diverse interactions between crops and environmental factors, it is surprising that evolutionary principles have been underexploited in addressing these food and environmental challenges. Compared with domesticated cultivars, crop wild relatives (CWRs) have been challenged in natural environments for thousands of years and maintain a much higher level of genetic diversity. In this review, we highlight the significance of CWRs for crop improvement by providing examples of CWRs that have been used to increase biotic and abiotic stress resistance/tolerance and overall yield in various crop species. We also discuss the surge of advanced biotechnologies, such as next-generation sequencing technologies and omics, with particular emphasis on how they have facilitated gene discovery in CWRs. We end the review by discussing the available resources and conservation of CWRs, including the urgent need for CWR prioritization and collection to ensure continuous crop improvement for food sustainability.

Genetic Diversity and Molecular Evolution of a Violaxanthin De-epoxidase Gene in Maize

Violaxanthin de-epoxidase (VDE) has a critical role in the carotenoid biosynthesis pathway, which is involved in protecting the photosynthesis apparatus from damage caused by excessive light. Here, a VDE gene in maize, ZmVDE1, was cloned and shown to have functional domains in common with the gramineous VDE protein. Candidate gene association analysis indicated that no polymorphic sites in ZmVDE1 were significant association with any of the examined carotenoid-related traits at P = 0.05 in an association panel containing 155 maize inbred lines. Nucleotide diversity analysis of VDE1 in maize and teosinte indicated that its exon had less genetic variation, consistent with the conserved function of VDE1 in plants. In addition, dramatically reduced nucleotide diversity, fewer haplotypes and a significantly negative parameter deviation for Tajima’s D test of ZmVDE1 in maize and teosinte suggested that a potential selective force had acted across the ZmVDE1 locus. We further identified a 4.2 Mb selective sweep with low recombination surrounding the ZmVDE1 locus that resulted in severely reduced nucleotide diversity on chromosome 2. Collectively, natural selection and the conserved domains of ZmVDE1 might show an important role in the xanthophyll cycle of the carotenoid biosynthesis pathway.

Molecular Evolution and Association of Natural Variation in ZmARF31 with Low Phosphorus Tolerance in Maize

Low-phosphorus (P) stress is one of the major factors constraining plant growth and yield. Improving plant tolerance to P starvation through molecular breeding is an efficient alternative to increase grain production. In the study, 331 diverse maize inbreds were used to detect nucleotide diversity and favorable alleles of ZmARF31, which plays a key role in low P responses and root architecture regulation. Significant phenotypic variation was found in each of 11 tested traits under both P and no-P treatments, and 30 single nucleotide polymorphisms (SNPs) and 14 insertion-deletions (InDels) were detected in ZmARF31 among the 331 maize inbreds. The 5'-untranslated region (UTR) of ZmARF31 showed a small linkage disequilibrium (LD) block under significant purifying selection, whereas the 3'-UTR showed the most abundant diversity and a larger LD block. Thirty, fourteen, and nine natural variations were identified in ZmARF31 that were associated with P-deficiency-tolerance traits (P ≤ 0.01) by using the general linear model (GLM), GLM incorporated with population structure, and mixed linear model, respectively. Four SNPs were significantly associated with the total dry weight (TDW) in the three models, of which SNPs S410 and S462 were located in a complete LD block. A further verification conducted in a recombinant inbred line population revealed that favorable allele G/G of non-synonymous mutation S410 and favorable allele with a 38 bp insertion of InDel S1442 exhibited positive genetic effects on the TDW and total root tips, respectively. Expression analysis further confirmed that ZmARF31 was highly expressed in the roots of low-P-tolerant inbred 178. The protein encoded by ZmARF31 was located both in the nucleus and cytoplasm. Haplotypes carrying more favorable alleles showed a greater effect on phenotypic variation than single loci. Such haplotypes should be helpful to develop valuable genetic markers and perform maize molecular breeding.

Breeding signature of combining ability improvement revealed by a genomic variation map from recurrent selection population in Brassica napus

Combining ability is crucial for parent selection in crop hybrid breeding. The present investigation and results had revealed the underlying genetic factors which might contribute in adequate combining ability, further assisting in enhancing heterosis and stability. Here, we conducted a large-scale analysis of genomic variation in order to define genomic regions affecting the combining ability in recurrent selection population of rapeseed. A population of 175 individuals was genotyped with the Brassica60K SNP chip. 525 hybrids were assembled with three different testers and used to evaluate the general combining ability (GCA) in three environments. By detecting the changes of the genomic variation, we identified 376 potential genome regions, spanning 3.03% of rapeseed genome which provided QTL-level resolution on potentially selected variants. More than 96% of these regions were located in the C subgenome, indicating that C subgenome had sustained stronger selection pressure in the breeding program than the A subgenome. In addition, a high level of linkage disequilibrium in rapeseed genome was detected, suggesting that marker-assisted selection for the population improvement might be easily implemented. This study outlines the evidence for high GCA on a genomic level and provided underlying molecular mechanism for recurrent selection improvement in B. napus.