Assembling seed dormancy genes into a system identified their effects on seedbank longevity in weedy rice

Biotechnological frontiers in harnessing allelopathy for sustainable crop production

Allelopathy, the phenomenon in which plants release biochemical compounds that influence the growth and development of neighbouring plants, presents promising opportunities for revolutionizing agriculture towards sustainability. This abstract explores the role of biotechnological advancements in unlocking the potential of allelopathy for sustainable crop production and its applications in agriculture, ecology, and natural resource management. By combining molecular, genetic, biochemical, and bioinformatic tools, researchers can unravel the complexities of allelopathic interactions and their potential for sustainable crop production and environmental stewardship. The development of novel management methods for weed control is getting a lot of attention with the introduction of new genetic technologies such as Gene drive, Transgene technologies, Gene silencing, Marker-assisted selection (MAS), and Clustered regularly interspaced short palindromic repeats (CRISPR-Cas9). By strengthening competitive characteristics these tools hold great promise for boosting crops' ability to compete with weeds. Considering recent literature, this review highlights the genetic, transcriptomics, and metabolomics approaches to allelopathy. Employing allelopathic properties in agriculture offer sustainable benefits like natural weed management, pest management, and reduced chemical pollution, but challenges include environmental factors, toxicity, regulatory hurdles, and limited resources. Effective integration requires continued research, regulatory support, and farmer education​. Also, we aimed to identify the biotechnological domains requiring more investigation and to provide the basis for future advances through this assessment.

Identification of the rice Rc gene as a main regulator of seed survival under dry storage conditions

Seed deterioration during storage results in poor germination, reduced vigour, and non-uniform seedling emergence. The aging rate depends on storage conditions and genetic factors. This study aims to identify these genetic factors determining the longevity of rice (Oryza sativa L.) seeds stored under experimental aging conditions mimicking long-term dry storage. Genetic variation for tolerance to aging was studied in 300 Indica rice accessions by storing dry seeds under an elevated partial pressure of oxygen (EPPO) condition. A genome-wide association analysis identified 11 unique genomic regions for all measured germination parameters after aging, differing from those previously identified in rice under humid experimental aging conditions. The significant single nucleotide polymorphism in the most prominent region was located within the Rc gene, encoding a basic helix-loop-helix transcription factor. Storage experiments using near-isogenic rice lines (SD7-1D (Rc) and SD7-1d (rc) with the same allelic variation confirmed the role of the wildtype Rc gene, providing stronger tolerance to dry EPPO aging. In the seed pericarp, a functional Rc gene results in accumulation of proanthocyanidins, an important sub-class of flavonoids having strong antioxidant activity, which may explain the variation in tolerance to dry EPPO aging.

Transcriptomic and QTL Analysis of Seed Germination Vigor under Low Temperature in Weedy Rice WR04-6

Low temperature is one of the major factors affecting rice germination, and low temperature germination (LTG) is an important agronomic trait. Although significant progress has been made in the study of rice LTG, the molecular mechanism of LTG remains poorly understood. To explore more rice LTG gene resources, we first demonstrated that weedy rice WR04-6 (Oryza sativa f. spontanea) had significantly higher LTG ability at 10 °C than the cultivated rice Qishanzhan (QSZ Oryza sativa L. ssp. indica). RNA-seq was used to investigate the gene expression of WR04-6 and QSZ at 10 °C for 10, 12 and 14 days after imbibition (DAI) of seed germination. The results of Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment revealed that the differentially expressed genes (DEGs) between WR04-6 and QSZ were mainly concentrated on the response to starch catabolic processes and the response to abscisic acid (ABA). This is consistent with the results of α-amylase activity, ABA and gibberellins (GA) treatment. A recombinant inbred line (RIL) population derived from a cross between WR04-6 and QSZ and its high-density SNP genetic map were used to detect quantitative trait loci (QTL) for LTG rates. The results showed that two new QTLs were located on chromosome 3 and chromosome 12. Combined with the mapped QTLs and RNA-seq DEGs, sixteen candidate genes potentially associated with LTG were identified. Validation of the expression of the candidates by qRT-PCR were consistent with the RNA-seq data. These results will enable us to understand the genetic basis of LTG in weedy rice and provide new genetic resources for the generation of rice germplasm with improved LTG.

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.

Biotechnological Road Map for Innovative Weed Management

In most agriculture farmlands, weed management is predominantly reliant on integrated weed management (IWM) strategies, such as herbicide application. However, the overuse and misuse of herbicides, coupled with the lack of novel active ingredients, has resulted in the uptrend of herbicide-resistant weeds globally. Moreover, weedy traits that contribute to weed seed bank persistence further exacerbate the challenges in weed management. Despite ongoing efforts in identifying and improving current weed management processes, the pressing need for novel control techniques in agricultural weed management should not be overlooked. The advent of CRISPR/Cas9 gene-editing systems, coupled with the recent advances in "omics" and cheaper sequencing technologies, has brought into focus the potential of managing weeds in farmlands through direct genetic control approaches, but could be achieved stably or transiently. These approaches encompass a range of technologies that could potentially manipulate expression of key genes in weeds to reduce its fitness and competitiveness, or, by altering the crop to improve its competitiveness or herbicide tolerance. The push for reducing or circumventing the use of chemicals in farmlands has provided an added incentive to develop practical and feasible molecular approaches for weed management, although there are significant technical, practical, and regulatory challenges for utilizing these prospective molecular technologies in weed management.

Increased Longevity and Dormancy of Soil-Buried Seeds from Advanced Crop–Wild Rice Hybrids Overexpressing the EPSPS Transgene

Simple Summary

Estimating the survival and reproductive ability caused by a transgene moved from a genetically engineered (GE) crop to its wild relative populations through gene flow plays an important role in assessing the potential environmental risks of the GE crop. Such estimation has essentially focused on the survival and reproduction-related characteristics above the ground, but with little attention to the GE seeds shattered in the soil seed banks. We demonstrated that the herbicide-resistant transgene overexpressing the rice endogenous EPSP enzyme increased the survival and longevity of the GE crop–wild (Oryza rufipogon) hybrid seeds in soil seed banks. In addition, enhanced survival and longevity of the GE hybrid seeds are likely associated with increases in seed dormancy and a growth hormone (auxin) via overexpressing the EPSPS transgene. Therefore, the EPSPS transgene can persist in the soil seed banks and spread in the environment, causing unwanted environmental impacts.

Abstract

Estimating the fitness effect conferred by a transgene introgressed into populations of wild relative species from a genetically engineered (GE) crop plays an important role in assessing the potential environmental risks caused by transgene flow. Such estimation has essentially focused on the survival and fecundity-related characteristics measured above the ground, but with little attention to the fate of GE seeds shattered in the soil seed banks after maturation. To explore the survival and longevity of GE seeds in soil, we examined the germination behaviors of crop–wild hybrid seeds (F₄–F₆) from the lineages of a GE herbicide-tolerant rice (Oryzasativa) line that contains an endogenous EPSPS transgene hybridized with two wild O. rufipogon populations after the seeds were buried in soil. The results showed significantly increased germination of the GE crop–wild hybrid seeds after soil burial, compared with that of the non-GE hybrid seeds. Additionally, the proportion of dormant seeds and the content of the growth hormone auxin (indole-3-acetic acid, IAA) in the GE crop–wild hybrid seeds significantly increased. Evidently, the EPSPS transgene enhances the survival and longevity of GE crop–wild rice seeds in the soil seed banks. The enhanced survival and longevity of the GE hybrid seeds is likely associated with the increases in seed dormancy and auxin (IAA) by overexpressing the rice endogenous EPSPS transgene. Thus, the fate of GE seeds in the soil seed banks should be earnestly considered when assessing the environmental risks caused by transgene flow.

Italian weedy rice-A case of de-domestication?

Weedy rice is a representative of the extensive group of feral weeds that derive from crops, but has returned to the lifestyle of a wild species. These weeds develop either from a hybridization of crops with wild relatives (exoferality), or by mutation of crops to weedy forms (endoferality). Due to the close relation of weed and crop, the methods for weed-targeted containment are limited to date. A deeper understanding of the development of such weeds might help to design more efficient and sustainable approaches for weed management. Weedy rice poses a serious threat to rice yields worldwide. It is widely accepted that weedy rice has originated independently in different regions all over the world. However, details of its evolution have remained elusive. In the current study, we investigated the history of weedy rice in northern Italy, the most important rice-growing area in Europe. Our approach was to analyze genes related to weedy traits (SD1, sh4, Rc) in weedy rice accessions compared to cultivars, and to integrate these results with phenotypic and physiological data, as well as historical information about rice farming in Italy. We arrive at a working model for the timeline of evolution of weedy rice in Italy indicating that both exoferality and endoferality acted as forces driving the development of the diverse weedy rice populations found in the region today. Models of weed evolution can help to predict the direction which weed development might take and to develop new, sustainable methods to control feral weeds.

Weedy Rice as a Novel Gene Resource: A Genome-Wide Association Study of Anthocyanin Biosynthesis and an Evaluation of Nutritional Quality

The pericarp color of rice grains is an important agronomic trait affected by domestication, and the color pigment, anthocyanin, is one of the key determinants of rice nutritional quality. Weedy rice, also called red rice because its pericarp is often red, may be a novel gene resource for the development of new rice. However, the genetic basis and nutritional quality of anthocyanin are poorly known. In this study, we used a genome-wide association study (GWAS) to find novel and specific QTLs of red pericarp in weedy rice. The known key gene site of red pericarp Rc was detected as the common genetic basis of both weedy and cultivated rice, and another 13 associated signals of pericarp color that were identified may contribute specifically to weedy rice pericarp color. We then nominated three pericarp color genes that may contribute to weedy rice divergence from cultivated rice based on selection sweep analysis. After clarifying the distribution and growth dynamics of pigment in weedy rice caryopsis, we compared its nutritional quality with cultivated rice. We found that sampled weedy rice pericarps had much greater quantities of anthocyanin, beneficial trace elements, free amino acids, and unsaturated fatty acids than the cultivated rice. In conclusion, the gene resources and novel genetic systems of rice anthocyanin biosynthesis explored in this study are of great value for the development of nutritious, high anthocyanin content rice.