Genomic revolution of US weedy rice in response to 21st century agricultural technologies

Genomic variation, environmental adaptation, and feralization in ramie, an ancient fiber crop

Feralization is an important evolutionary process, but the mechanisms behind it remain poorly understood. Here, we use the ancient fiber crop ramie (Boehmeria nivea (L.) Gaudich.) as a model to investigate genomic changes associated with both domestication and feralization. We first produced a chromosome-scale de novo genome assembly of feral ramie and investigated structural variations between feral and domesticated ramie genomes. Next, we gathered 915 accessions from 23 countries, comprising cultivars, major landraces, feral populations, and the wild progenitor. Based on whole-genome resequencing of these accessions, we constructed the most comprehensive ramie genomic variation map to date. Phylogenetic, demographic, and admixture signal detection analyses indicated that feral ramie is of exoferal or exo-endo origin, i.e., descended from hybridization between domesticated ramie and the wild progenitor or ancient landraces. Feral ramie has higher genetic diversity than wild or domesticated ramie, and genomic regions affected by natural selection during feralization differ from those under selection during domestication. Ecological analyses showed that feral and domesticated ramie have similar ecological niches that differ substantially from the niche of the wild progenitor, and three environmental variables are associated with habitat-specific adaptation in feral ramie. These findings advance our understanding of feralization, providing a scientific basis for the excavation of new crop germplasm resources and offering novel insights into the evolution of feralization in nature.

Weed biology and management in the multi-omics era: Progress and perspectives

Weeds pose a significant threat to crop production, resulting in substantial yield reduction. In addition, they possess robust weedy traits that enable them to survive in extreme environments and evade human control. In recent years, the application of multi-omics biotechnologies has helped to reveal the molecular mechanisms underlying these weedy traits. In this review, we systematically describe diverse applications of multi-omics platforms for characterizing key aspects of weed biology, including the origins of weed species, weed classification, and the underlying genetic and molecular bases of important weedy traits such as crop-weed interactions, adaptability to different environments, photoperiodic flowering responses, and herbicide resistance. In addition, we discuss limitations to the application of multi-omics techniques in weed science, particularly compared with their extensive use in model plants and crops. In this regard, we provide a forward-looking perspective on the future application of multi-omics technologies to weed science research. These powerful tools hold great promise for comprehensively and efficiently unraveling the intricate molecular genetic mechanisms that underlie weedy traits. The resulting advances will facilitate the development of sustainable and highly effective weed management strategies, promoting greener practices in agriculture.

Harnessing weedy rice as functional food and source of novel traits for crop improvement

A relative of cultivated rice (Oryza sativa L.), weedy or red rice (Oryza spp.) is currently recognized as the dominant weed, leading to a drastic loss of yield of cultivated rice due to its highly competitive abilities like producing more tillers, panicles, and biomass with better nutrient uptake. Due to its high nutritional value, antioxidant properties (anthocyanin and proanthocyanin), and nutrient absorption ability, weedy rice is gaining immense research attentions to understand its genetic constitution to augment future breeding strategies and to develop nutrition-rich functional foods. Consequently, this review focuses on the unique gene source of weedy rice to enhance the cultivated rice for its crucial features like water use efficiency, abiotic and biotic stress tolerance, early flowering, and the red pericarp of the seed. It explores the debating issues on the origin and evolution of weedy rice, including its high diversity, signalling aspects, quantitative trait loci (QTL) mapping under stress conditions, the intricacy of the mechanism in the expression of the gene flow, and ecological challenges of nutrient removal by weedy rice. This review may create a foundation for future researchers to understand the gene flow between cultivated crops and weedy traits and support an improved approach for the applicability of several models in predicting multiomics variables.

Gene flow and spontaneous mutations are responsible for imidazolinone herbicide-resistant weedy rice (Oryza sativa L.)

For more than two decades, weedy rice (Oryza sativa L.) has been controlled in rice fields by using imidazolinone (IMI) herbicide-resistant rice technology (Clearfield®). Outcrossing in weedy rice populations and spontaneous mutations are potential problems with herbicide-resistant crop management technologies, such as the IMI-resistant rice. The aim of this study was to characterize the mechanism of IMI herbicide resistance in weedy rice through dose-response bioassay study and evaluating amino acid substitutions in acetolactate synthase (ALS) protein. A total of 118 suspected IMI-resistant weedy rice samples, which survived in the field after an IMI herbicide application, were collected at harvest time from Türkiye in 2020 and 2021. Single-dose imazamox application experiment revealed that 38 plants survived herbicide treatment. The imazamox resistance of the surviving plants was confirmed by dose-response experiment. ALS gene region underwent a sanger DNA partial sequencing. No substitution was found in 10 samples, however, amino acid substitutions were found in 26 samples with S563N, one sample with S653T, and one sample with E630D. The S653N point is the same substitution point that serves as the origin of resistance for the Clearfield® rice varieties that are commonly cultivated in the region. It has been hypothesized that the gene flow from IMI-resistant rice may be the cause of resistance in the IMI resistant weedy rice samples with S653N. The other substitution, S653T, were considered spontaneous mutation to IMI resistance. Interestingly, the S653T mutation was detected for the first time in weedy rice. The mechanism of resistance of 10 resistant weedy rice was not confirmed in this study, however, it may be a non-target resistance or another mutation point in target site, but evidently, they did not acquire resistance by gene flow from IMI-resistant rice. It has been concluded that the effectiveness of IMI-resistant rice technology in controlling weedy rice has drastically decreased due to possible gene flow, spontaneous mutation and non-target resistance. In addition to cultural controls like clean seed, clean machinery and crop rotation, other herbicide-tolerant rice systems such as Provisia® and Roxy-RPS® rice are needed to create a diverse weedy rice management ensemble available for rice production and move towards sustainable rice farming.

A derived weedy rice × ancestral cultivar cross identifies evolutionarily relevant weediness QTLs

Weedy rice (Oryza spp.) is a weedy relative of the cultivated rice that competes with the crop and causes significant production loss. The BHA (blackhull awned) US weedy rice group has evolved from aus cultivated rice and differs from its ancestors in several important weediness traits, including flowering time, plant height and seed shattering. Prior attempts to determine the genetic basis of weediness traits in plants using linkage mapping approaches have not often considered weed origins. However, the timing of divergence between crossed parents can affect the detection of quantitative trait loci (QTL) relevant to the evolution of weediness. Here, we used a QTL-seq approach that combines bulked segregant analysis and high-throughput whole genome resequencing to map the three important weediness traits in an F2 population derived from a cross between BHA weedy rice with an ancestral aus cultivar. We compared these QTLs with those previously detected in a cross of BHA with a more distantly related crop, indica. We identified multiple QTLs that overlapped with regions under selection during the evolution of weedy BHA rice and some candidate genes possibly underlying the evolution weediness traits in BHA. We showed that QTLs detected with ancestor-descendant crosses are more likely to be involved in the evolution of weediness traits than those detected from crosses of more diverged taxa.

Crop-Weed Introgression Plays Critical Roles in Genetic Differentiation and Diversity of Weedy Rice: A Case Study of Human-Influenced Weed Evolution

As an important driving force, introgression plays an essential role in shaping the evolution of plant species. However, knowledge concerning how introgression affects plant evolution in agroecosystems with strong human influences is still limited. To generate such knowledge, we used InDel (insertion/deletion) molecular fingerprints to determine the level of introgression from japonica rice cultivars into the indica type of weedy rice. We also analyzed the impact of crop-to-weed introgression on the genetic differentiation and diversity of weedy rice, using InDel (insertion/deletion) and SSR (simple sequence repeat) molecular fingerprints. Results based on the STRUCTURE analysis indicated an evident admixture of some weedy rice samples with indica and japonica components, suggesting different levels of introgression from japonica rice cultivars to the indica type of weedy rice. The principal coordinate analyses indicated indica-japonica genetic differentiation among weedy rice samples, which was positively correlated with the introgression of japonica-specific alleles from the rice cultivars. In addition, increased crop-to-weed introgression formed a parabola pattern of dynamic genetic diversity in weedy rice. Our findings based on this case study provide evidence that human activities, such as the frequent change in crop varieties, can strongly influence weed evolution by altering genetic differentiation and genetic diversity through crop-weed introgression in agroecosystems.

Weed genomics: yielding insights into the genetics of weedy traits for crop improvement

Weeds cause tremendous economic and ecological damage worldwide. The number of genomes established for weed species has sharply increased during the recent decade, with some 26 weed species having been sequenced and de novo genomes assembled. These genomes range from 270 Mb (Barbarea vulgaris) to almost 4.4 Gb (Aegilops tauschii). Importantly, chromosome-level assemblies are now available for 17 of these 26 species, and genomic investigations on weed populations have been conducted in at least 12 species. The resulting genomic data have greatly facilitated studies of weed management and biology, especially origin and evolution. Available weed genomes have indeed revealed valuable weed-derived genetic materials for crop improvement. In this review, we summarize the recent progress made in weed genomics and provide a perspective for further exploitation in this emerging field.

Agricultural weeds: the contribution of domesticated species to the origin and evolution of feral weeds

Agricultural weeds descended from domesticated ancestors, directly from crops (endoferality) and/or from crop-wild hybridization (exoferality), may have evolutionary advantages by rapidly acquiring traits pre-adapted to agricultural habitats. Understanding the role of crops on the origin and evolution of agricultural weeds is essential to develop more effective weed management programs, minimize crop losses due to weeds, and accurately assess the risks of cultivated genes escaping. In this review, we first describe relevant traits of weediness: shattering, seed dormancy, branching, early flowering and rapid growth, and their role in the feralization process. Furthermore, we discuss how the design of "super-crops" can affect weed evolution. We then searched for literature documenting cases of agricultural weeds descended from well-domesticated crops, and describe six case studies of feral weeds evolved from major crops: maize, radish, rapeseed, rice, sorghum, and sunflower. Further studies on the origin and evolution of feral weeds can improve our understanding of the physiological and genetic mechanisms underpinning the adaptation to agricultural habitats and may help to develop more effective weed-control practices and breeding better crops. © 2022 Society of Chemical Industry.

Hybrid-derived weedy rice maintains adaptive combinations of alleles associated with seed dormancy

Plant hybridization is a pathway for the evolution of adaptive traits. However, hybridization between adapted and nonadapted populations may affect the persistence of combinations of adaptive alleles evolved through natural selection. Seed dormancy is an adaptive trait for weedy rice because it regulates the timing of seed germination and the persistence of the soil seed bank. Hybridization between weedy and cultivated rice has been confirmed with an adaptive introgression of deep seed dormancy alleles from cultivated rice. Here, we explored the influence of hybridization on the conservation of adaptive allele combinations by evaluating natural variation and genetic structure in seed dormancy-associated genomic regions. Based on sequence variation in the genomic regions associated with seed dormancy, hybrid-derived weedy rice strains maintained most of the adaptive combinations for this trait observed in the parental weedy rice, despite equal representation of the parental weedy and cultivated rice in the whole genome sequence. Moreover, hybrid-derived weedy rice strains were more dormant than their parental weedy rice strains, and this trait was strongly influenced by the environment. This study suggests that hybridization between weedy rice (adaptive allelic combinations for seed dormancy) and cultivated rice (nonadaptive combinations) generates weedy rice strains expressing deep seed dormancy caused by genome stabilization through the removal of alleles derived from cultivated rice, in addition to the adaptive introgression of deep seed dormancy alleles derived from cultivated rice. Thus, hybridization between adapted and nonadapted populations appears to be reinforcing the trajectory towards the evolution of adaptive traits.