Extensive allelic variation in agronomically important genes serves as the basis of rice breeding. Here, we present a comprehensive map of rice quantitative trait nucleotides (QTNs) and inferred QTN ...effects based on eight genome-wide association study cohorts. Population genetic analyses revealed that domestication, local adaptation and heterosis are all associated with QTN allele frequency changes. A genome navigation system, RiceNavi, was developed for QTN pyramiding and breeding route optimization, and implemented in the improvement of a widely cultivated indica variety. This work presents an efficient platform that bridges ever-increasing genomic knowledge and diverse improvement needs in rice.
Human selection during crop domestication has resulted in remarkable transformations of plant phenotypes, providing a window into the genetic basis of morphological evolution. Recent progress in our ...understanding of the genetic architecture of novel plant traits has emerged from combining advanced molecular technologies with improved experimental designs, including nested association mapping, genome-wide association studies, population genetic screens for signatures of selection, and candidate gene approaches. These studies reveal a diversity of underlying causative mutations affecting phenotypes important in plant domestication and crop improvement, including coding sequence substitutions, presence/absence and copy number variation, transposon activation leading to novel gene structures and expression patterns, diversification following gene duplication, and polyploidy leading to altered combinatorial capabilities. The genomic regions unknowingly targeted by human selection include both structural and regulatory genes, often with results that propagate through the transcriptome as well as to other levels in the biosynthetic and morphogenetic networks.
As a portable source of food, water, fuel, and construction materials, the coconut (Cocos nucifera L.) played a fundamental role in human migrations and the development of civilization across the ...humid tropics. Here we investigated the coconut's domestication history and its population genetic structure as it relates to human dispersal patterns. A sample of 1,322 coconut accessions, representing the geographical and phenotypic diversity of the species, was examined using ten microsatellite loci. Bayesian analyses reveal two highly genetically differentiated subpopulations that correspond to the Pacific and Indo-Atlantic oceanic basins. This pattern suggests independent origins of coconut cultivation in these two world regions, with persistent population structure on a global scale despite long-term human cultivation and dispersal. Pacific coconuts show additional genetic substructure corresponding to phenotypic and geographical subgroups; moreover, the traits that are most clearly associated with selection under human cultivation (dwarf habit, self-pollination, and "niu vai" fruit morphology) arose only in the Pacific. Coconuts that show evidence of genetic admixture between the Pacific and Indo-Atlantic groups occur primarily in the southwestern Indian Ocean. This pattern is consistent with human introductions of Pacific coconuts along the ancient Austronesian trade route connecting Madagascar to Southeast Asia. Admixture in coastal east Africa may also reflect later historic Arab trading along the Indian Ocean coastline. We propose two geographical origins of coconut cultivation: island Southeast Asia and southern margins of the Indian subcontinent.
Genome scans for selection can provide an efficient way to dissect the genetic basis of domestication traits and understand mechanisms of adaptation during crop evolution. Selection involving soft ...sweeps (simultaneous selection for multiple alleles) is probably common in plant genomes but is under‐studied, and few if any studies have systematically scanned for soft sweeps in the context of crop domestication. Using genome resequencing data from 302 wild and domesticated soybean accessions, we conducted selection scans using five widely employed statistics to identify selection candidates under classical (hard) and soft sweeps. Across the genome, inferred hard sweeps are predominant in domesticated soybean landraces and improved varieties, whereas soft sweeps are more prevalent in a representative subpopulation of the wild ancestor. Six domestication‐related genes, representing both hard and soft sweeps and different stages of domestication, were used as positive controls to assess the detectability of domestication‐associated sweeps. Performance of various test statistics suggests that differentiation‐based (FST) methods are robust for detecting complete hard sweeps, and that LD‐based strategies perform well for identifying recent/ongoing sweeps; however, none of the test statistics detected a known soft sweep we previously documented at the domestication gene Dt1. Genome scans yielded a set of 66 candidate loci that were identified by both differentiation‐based and LD‐based (iHH) methods; notably, this shared set overlaps with many previously identified QTLs for soybean domestication/improvement traits. Collectively, our results will help to advance genetic characterizations of soybean domestication traits and shed light on selection modes involved in adaptation in domesticated plant species.
The process of crop domestication has long been a topic of active research for biologists, anthropologists and others. Genetic data have proved a powerful resource for drawing inferences on questions ...regarding the geographical origins of crops, the numbers of independent domestication events for a given crop species, the specific molecular changes underlying domestication traits, and the nature of artificial selection during domestication and subsequent crop improvement. We would argue that these genetic inferences are fundamentally compatible with recent archaeological data that support a view of domestication as a geographically diffuse, gradual process. In this review, we summarize methodologies ranging from quantitative trait locus mapping to resequencing used in genetic analyses of crop evolution. We also highlight recent major insights regarding the timing and spatial patterning of crop domestication and the distinct genetic underpinnings of domestication, diversification and improvement traits.
There is growing evidence for the convergent evolution of physically linked gene clusters encoding chemical defense pathways. Metabolic clusters are proposed to evolve because they ensure ...co-inheritance of all required genes where the defense is favored, and prevent inheritance of toxic partial pathways where it is not. This hypothesis rests on the assumption that clusters evolve in species where selection favors intraspecific polymorphism for the defense; however, they have not been examined in polymorphic species.
We examined metabolic cluster evolution in relation to an adaptive polymorphism for cyanogenic glucoside (CNglc) production in clover. Using 163 accessions, we performed CNglc assays, BAC sequencing, Southern hybridizations and molecular evolutionary analyses.
We find that the CNglc pathway forms a 138-kb cluster in white clover, and that the adaptive polymorphism occurs through presence/absence of the complete cluster. Component genes are orthologous to those in the distantly related legume Lotus japonicus.
These findings provide empirical support for the co-inheritance hypothesis, and they indicate that adaptive CNglc variation in white clover evolves through recurrent deletions of the entire pathway. They further indicate that the shared ancestor of many important legume crops was likely cyanogenic and that this defense was lost repeatedly over the last 50 Myr.
Crop domestication provided the calories that fueled the rise of civilization. For many crop species, domestication was accompanied by the evolution of weedy crop relatives, which aggressively ...outcompete crops and reduce harvests. Understanding the genetic mechanisms that underlie the evolution of weedy crop relatives is critical for agricultural weed management and food security. Here we use whole-genome sequences to examine the origin and adaptation of the two major strains of weedy rice found in the United States. We find that de-domestication from cultivated ancestors has had a major role in their evolution, with relatively few genetic changes required for the emergence of weediness traits. Weed strains likely evolved both early and late in the history of rice cultivation and represent an under-recognized component of the domestication process. Genomic regions identified here that show evidence of selection can be considered candidates for future genetic and functional analyses for rice improvement.
Worldwide feralization of crop species into agricultural weeds threatens global food security. Weedy rice is a feral form of rice that infests paddies worldwide and aggressively outcompetes ...cultivated varieties. Despite increasing attention in recent years, a comprehensive understanding of the origins of weedy crop relatives and how a universal feralization process acts at the genomic and molecular level to allow the rapid adaptation to weediness are still yet to be explored.
We use whole-genome sequencing to examine the origin and adaptation of 524 global weedy rice samples representing all major regions of rice cultivation. Weed populations have evolved multiple times from cultivated rice, and a strikingly high proportion of contemporary Asian weed strains can be traced to a few Green Revolution cultivars that were widely grown in the late twentieth century. Latin American weedy rice stands out in having originated through extensive hybridization. Selection scans indicate that most genomic regions underlying weedy adaptations do not overlap with domestication targets of selection, suggesting that feralization occurs largely through changes at loci unrelated to domestication.
This is the first investigation to provide detailed genomic characterizations of weedy rice on a global scale, and the results reveal diverse genetic mechanisms underlying worldwide convergent rice feralization.
PDF
