White star apple (Gambeya albida) is native to the lowland rainforests of Central, East, and West Africa. This species is highly valued for its nutritious fruits and offers medicinal, socio-cultural, and economic benefits. In West Africa, it contributes to food security for rural and urban communities alike. However, no genomic resources are available to untap the agronomic and medicinal traits of the white star apple. Here, we present its first chromosome-scale genome, generated using PacBio HiFi and Omni-C sequencing. The white star apple genome is highly homozygous, and we assembled 98.9% of the estimated haploid genome size (822 Mbp) into 13 pseudochromosomes. It has a base-level accuracy (QV) of 58.14, an N50 of 57 Mbp, and 97.5% BUSCO completeness, representing a reference-quality assembly. About 58.5% of the genome constitutes repetitive sequences, and ab initio gene prediction identified 33,602 gene models. This reference-quality genome of the white star apple will serve as a valuable resource to enhance our understanding of its nutritional and pharmacological traits and facilitate improvement research.

The carbohydrate-rich storage roots of cassava (Manihot esculenta) are among the world's most vital staple foods, providing food security and income for hundreds of millions of people-primarily small-holder farmers in tropical and subtropical regions. Cassava is also a major source of starch for both food and industrial applications. Root yield is largely determined by starch content, which acts as the main sink for photoassimilates during vegetative growth. In addition, stored starch serves as a carbohydrate reservoir that supports regrowth after stress events, such as drought or shoot pruning, or during stem propagation. To investigate source-sink dynamics and identify key factors in sink metabolism, transcriptomic and proteomic analyses of cassava storage roots were conducted following shoot pruning. This perturbation led to a significant reduction in root starch content and triggered widespread transcriptional reprogramming, restricting respiration and growth. Notably, key starch biosynthesis genes were repressed, while starch degradation genes-including the plastidial α-AMYLASE3 A (AMY3A)-were induced. To confirm the role of AMY3 in root starch breakdown, AMY3A-suppressed cassava lines were generated via RNA interference and evaluated under both greenhouse and field conditions. These lines exhibited up to a 7.5-fold reduction in starch mobilization following pruning compared to controls, demonstrating AMY3's key function in storage root starch degradation-a role that contrasts with its redundancy in systems like transitory starch degradation in Arabidopsis leaves. Crucially, AMY3A suppression did not impair cassava stem cutting regrowth, highlighting it as a promising target for improving cassava root traits and advancing food security.

Abstract Cassava ( Manihot esculenta Crantz) is a major staple crop across tropical and subtropical regions. Despite advances in genomic selection, delayed, non-flowering, and asynchronous flowering remain key bottlenecks in breeding programs. To better understand the molecular basis of flowering-time variation, we performed RNA sequencing across three genotypes with contrasting flowering phenotypes (early, late, and non-flowering) sampled at three developmental stages under contrasting light regimes in field conditions (natural light and three-hour night-break with white light). Comparative transcriptomic analysis revealed distinct gene expression patterns associated with flowering responses. Genotype comparisons with no light supplementation revealed stage-specific enrichment of biological processes. Light supplementation was associated with changes in the expression of key components of photoperiodic and circadian regulation, as well as pathways involved in flowering-time integration and hormone and sugar-related signaling. These findings suggest that coordinated changes across multiple biological pathways regulate flowering behavior in cassava. The candidate genes and expression patterns reported provide a foundation for functional studies and advance our understanding of molecular mechanisms governing flowering-time regulation in cassava.

The African BioGenome Project (AfricaBP) is a Pan-African initiative aimed at improving food systems and biodiversity conservation through genomics while ensuring equitable data sharing and benefits. The Open Institute is the knowledge exchange platform of the AfricaBP which aims to bridge local knowledge gaps in biodiversity genomics and bioinformatics and enable infrastructural developments. In 2024, the AfricaBP Open Institute advanced this mission by organising 31 workshops that attracted more than 3500 registered attendees and trained 380 African researchers in genomics, bioinformatics, molecular biology, sample collections and biobanking, and ethics, across all five African geographical regions involving 40 African and non-African organizations. These workshops provide current understanding on the applications of biodiversity genomics and bioinformatics to the African bioeconomy as well as providing practical and hands-on training in genomics, bioinformatics, molecular biology, gene editing, and sample collection and processing. Here, we provide the current understanding of the applications of biodiversity genomics and bioinformatics to the African bioeconomy through synthetic reviews and presentations, including descriptions of 31 workshops organised as well as three fellowship programs delivered or launched by the AfricaBP Open Institute in collaboration with African and international institutions and industry partners. We review the current national bioeconomy strategies across Africa and the economic impact of sequencing African genomes locally, illustrated by a case study on the proposed 1000 Moroccan Genome Project. Finally, we provide recommendations on how African countries could integrate biodiversity genomics and bioinformatics into national economic plans and bioeconomy strategies.

Cassava (Manihot esculenta, Crantz) is a perennial crop cultivated in tropical and subtropical areas. In its cultivation cycle, it encounters environmental stresses related to changes in temperature and water fluctuations during seasonal transitions. We profiled the transcriptomes of four field-grown genotypes to investigate the molecular basis of adaptation to season transitions. 3’mRNA-seq libraries were prepared from samples collected from storage roots to capture gene expression changes associated with shifts from rainy to dry and dry to rainy seasons. Reproducibility and variability within the dataset were evaluated using correlation analysis and principal component analysis, providing confidence in data quality and consistency across samples. The usability of these data was proved by differential expression analysis during the rainy-to-dry and dry-to-rainy transitions, and by functional enrichment analysis. The detailed information of the experimental environmental conditions and of the workflow from planting to final DEGs analysis provided, make this dataset a useful resource for future research on plant responses to environmental fluctuations and to identify candidate genes for crop improvement strategies for climate-resilient varieties.

The African BioGenome Project (AfricaBP) is a Pan-African initiative aimed at improving food systems and biodiversity conservation through genomics while ensuring equitable data sharing and benefits. The Open Institute is the knowledge exchange platform of the AfricaBP, which aims to bridge local knowledge gaps in biodiversity genomics and bioinformatics and enable infrastructural developments. In 2024, the AfricaBP Open Institute advanced this mission by organizing 31 workshops that attracted more than 3500 registered attendees across 50 African countries, provided training to 401 African researchers in genomics, bioinformatics, molecular biology, sample collections and biobanking, and ethical considerations, across all five African geographical regions involving 40 African and non-African organizations. These workshops provide insights on applications of biodiversity genomics and bioinformatics to the African bioeconomy, as well as hands-on training in sample collection and processing, genomics, bioinformatics, molecular biology, and gene editing. Here, we provide the current understanding of the applications of biodiversity genomics and bioinformatics to the African bioeconomy through synthetic reviews and presentations, including descriptions of 31 workshops organized as well as three fellowship programs delivered or launched by the AfricaBP Open Institute in collaboration with African and international institutions and industry partners. We review the current national bioeconomy strategies across Africa and the economic impact of sequencing African genomes locally, illustrated by a case study on the proposed 1000 Moroccan Genome Project. Key recommendations include integrating biodiversity genomics and bioinformatics into national bioeconomy strategies, leveraging genomics for sustainable bioeconomy growth, and expanding capacity-building initiatives across Africa.

Structural variants (SVs) are critical for plant genomic diversity and phenotypic variation. This study investigates a large, 9.7 Mbp highly repetitive segment on chromosome 12 of TMEB117, a region not previously characterized in cassava (Manihot esculenta Crantz). We aim to explore its presence and variability across multiple cassava landraces, providing insights into its genomic significance and potential implications. We validated the presence of the 9.7 Mbp segment in the TMEB117 genome, distinguishing it from other published cassava genome assemblies. By mapping short-read sequencing data from 16 cassava landraces to TMEB117 chromosome 12, we observed variability in read mapping, suggesting that while all genotypes contain the insertion region, some exhibit missing segments or sequence differences. Further analysis revealed two unique genes associated with deacetylase activity, HDA14 and SRT2, within the insertion. Additionally, the MUDR-Mutator transposable element was significantly overrepresented in this region. This study uncovers a large structural variant in the TMEB117 cassava genome, highlighting its variability among different genotypes. The enrichment of HDA14 and SRT2 genes and the MUDR-Mutator elements within the insertion suggests potential functional significance, though further research is needed to explore this. These findings provide important insights into the role of structural variations in shaping cassava genomic diversity.

Plant-pathogen interactions activate molecular activities wherein the host defends the pathogen while the pathogen tries to suppress the plant response. Small RNAs (sRNAs) mediate major mechanisms, including post-transcriptional gene silencing, histone modification and DNA methylation by which plants respond to the presence of pathogens. Genome-wide profiling of host and pathogen sRNAs is therefore pivotal to uncovering the mechanisms underlying the host-pathogen interaction and mechanisms for host resistance. sRNA high throughput sequencing (HTS) data analysis often involves multiple stages/tools. Most necessary tools are accessible only through the command line, making it challenging for those without a high level of Unix/Linux skills. Furthermore, installation of some of these tools may become difficult due to dependencies and software version compatibility. We have developed an integrated open-source pipeline, Ds-Seq, for end-to-end in silico analysis of sRNA HTS data with improved reproducibility. The pipeline combines in-house scripts and public tools in a shell script, which can be invoked with a single command. The pipeline's usefulness has been demonstrated with testing on publicly available and published data from independent sRNA-seq datasets of host-pathogen interaction studies. Ds-Seq is available on GitHub, while a Docker image can be obtained from the Docker hub.Availability: Ds-Seq is freely available from the GitHub repository at https://github.com/CEPHAS-01/small-RNASeq.ngs and Docker hub with ID cephas/ds-seq (https://hub.docker.com/r/cephas/ds-seq).

Cassava ( Manihot esculenta Crantz ) is a vital tropical root crop providing essential dietary energy to over 800 million people in tropical and subtropical regions. As a climate-resilient crop, its significance grows as the human population expands. However, yield improvement faces challenges from biotic and abiotic stress and limited breeding. Advanced sequencing and assembly techniques enabled the generation of a highly accurate, nearly complete, haplotype-resolved genome of the African cassava cultivar TMEB117. It is the most accurate cassava genome sequence to date with a base-level accuracy of QV > 64, N50 > 35 Mbp, and 98.9% BUSCO completeness. Over 60% of the genome comprises repetitive elements. We predicted over 45,000 gene models for both haplotypes. This achievement offers valuable insights into the heterozygosity genome organization of the cassava genome, with improved accuracy, completeness, and phased genomes. Due to its high susceptibility to African Cassava Mosaic Virus (ACMV) infections compared to other cassava varieties, TMEB117 provides an ideal reference for studying virus resistance mechanisms, including epigenetic variations and smallRNA expressions.

Chlorosis is frequently incited by viroids, small nonprotein-coding, circular RNAs replicating in nuclei (family Pospiviroidae) or chloroplasts (family Avsunviroidae). Here, we investigated how chrysanthemum chlorotic mottle viroid (CChMVd, Avsunviroidae) colonizes, evolves and initiates disease. Progeny variants of natural and mutated CChMVd sequence variants inoculated in chrysanthemum plants were characterized, and plant responses were assessed by molecular assays. We showed that: chlorotic mottle induced by CChMVd reflects the spatial distribution and evolutionary behaviour in the infected host of pathogenic (containing a UUUC tetranucleotide) and nonpathogenic (lacking such a pathogenic determinant) variants; and RNA silencing is involved in the initiation of the chlorosis in symptomatic leaf sectors through a viroid-derived small RNA containing the pathogenic determinant that directs AGO1-mediated cleavage of the mRNA encoding the chloroplastic transketolase. This study provides the first evidence that colonization of leaf tissues by CChMVd is characterized by segregating variant populations differing in pathogenicity and with the ability to colonize leaf sectors (bottlenecks) and exclude other variants (superinfection exclusion). Importantly, no specific pathogenic viroid variants were found in the chlorotic spots caused by chrysanthemum stunt viroid (Pospiviroidae), thus establishing a clear distinction on how members of the two viroid families trigger chlorosis in the same host.

EpiCass and CassavaNet4Dev are collaborative projects funded by the Swedish Research Council between the Swedish University of Agriculture (SLU) and the International Institute of Tropical Agriculture (IITA). The projects aim to investigate the influence of epigenetic changes on agricultural traits such as yield and virus resistance while also providing African students and researchers with advanced bioinformatics training and opportunities to participate in big data analysis events. The first advanced bioinformatics training workshop took place from May 16th to May 18th, 2022, followed by an online mini-symposium titled "Epigenetics and crop improvement" on May 19th. The symposium featured international speakers covering a wide range of topics related to plant epigenetics, cassava viral diseases, and cassava breeding strategies. A new online and on-site teaching concept was developed for the three-day workshop to ensure maximum student participation across Western, Eastern, and Southern Africa. Initially planned in Nigeria, Kenya, Ethiopia, Tanzania, and Zambia, the workshop ultimately focused on Nigeria, Kenya, and Ethiopia due to a lack of qualified candidates in the other countries. Each classroom hosted 20 to 25 students, with at least one bioinformatician present for support. The classrooms were connected via video conferencing, whereas teachers located in different places in Africa and Europe joined the video stream to conduct teaching sessions. The workshop was divided into theoretical classes and hands-on sessions, where participants could run data analysis with support from online teachers and local bioinformaticians. To enable participants to run guided, CPU and RAM-intensive data analysis workflows and overcome local computing and internet access restrictions, a system of virtual machines (VMs) hosted in the cloud was developed. The teaching platform provided teaching and exercise materials to support the use of the VMs. Although some students could not run heavy data analysis workflows due to unforeseen restrictions in the cloud, these issues were solved. All participants had the opportunity to run the analysis steps independently in the cloud using the protocols hosted on the teaching platform.

Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), short interfering RNAs (siRNAs), and long non-coding RNAs (lncRNAs), have emerged as pivotal regulators within the plant kingdom [...].

Cassava (Manihot esculenta Crantz) is a predominant food security crop in several developing countries. Its storage roots, rich in carbohydrate, are deficient in essential micronutrients, including provitamin A carotenoids. Increasing carotenoid content in cassava storage roots is important to reduce the incidence of vitamin A deficiency, a public health problem in sub-Saharan Africa. However, cassava improvement advances slowly, mainly due to limited information on the molecular factors influencing β-carotene accumulation in cassava. To address this problem, we performed comparative transcriptomic and untargeted metabolic analyses of roots and leaves of eleven African cassava landraces ranging from white to deep yellow colour, to uncover regulators of carotenoid biosynthesis and accumulation with conserved function in yellow cassava roots. Sequence analysis confirmed the presence of a mutation, known to influence β-carotene content, in PSY transcripts of deep yellow but not of pale yellow genotypes. We identified genes and metabolites with expression and accumulation levels significantly associated with β-carotene content. Particularly an increased activity of the abscisic acid catabolism pathway together with a reduced amount of L-carnitine, may be related to the carotenoid pathway flux, higher in yellow than in white storage roots. In fact, NCED_3.1 was specifically expressed at a lower level in all yellow genotypes suggesting that it could be a potential target for increasing carotenoid accumulation in cassava. These results expand the knowledge on metabolite compositions and molecular mechanisms influencing carotenoid biosynthesis and accumulation in cassava and provide novel information for biotechnological applications and genetic improvement of cassava with high nutritional values.

Earth's life may have originated as self-replicating RNA, and it has been argued that RNA viruses and viroid-like elements are remnants of such pre-cellular RNA world. RNA viruses are defined by linear RNA genomes encoding an RNA-dependent RNA polymerase (RdRp), whereas viroid-like elements consist of small, single-stranded, circular RNA genomes that, in some cases, encode paired self-cleaving ribozymes. Here we show that the number of candidate viroid-like elements occurring in geographically and ecologically diverse niches is much higher than previously thought. We report that, amongst these circular genomes, fungal ambiviruses are viroid-like elements that undergo rolling circle replication and encode their own viral RdRp. Thus, ambiviruses are distinct infectious RNAs showing hybrid features of viroid-like RNAs and viruses. We also detected similar circular RNAs, containing active ribozymes and encoding RdRps, related to mitochondrial-like fungal viruses, highlighting fungi as an evolutionary hub for RNA viruses and viroid-like elements. Our findings point to a deep co-evolutionary history between RNA viruses and subviral elements and offer new perspectives in the origin and evolution of primordial infectious agents, and RNA life.

Striga hermonthica is the most widespread and destructive plant parasite infesting maize and other major crops in sub-Saharan Africa where it causes severe yield losses and threatens food security. Several tolerant maize lines supporting reduced S. hermonthica emergence have been deployed. However, the molecular bases of such resistance are yet poorly understood. Based on a time course comparative gene expression analysis between susceptible and resistant maize lines we have confirmed resistance mechanisms known to be activated upon plant parasite infestation and identified potential novel players worth further investigation e.g. iron homeostasis and mitochondrial respiration-related genes. Most intriguingly, we show a previously unknown strategy of maize post-attachment resistance based on DIMBOA accumulation in S. hermonthica-infested maize roots. S. hermonthica infestation triggers positive regulation of gene expression in the hydroxamic acid (HA) pathway culminating with an accumulation of benzoxazinoids (BX), known for their antifeedant, insecticidal, antimicrobial, and allelopathic activities. We demonstrate that HA root content is positively correlated with S. hermonthica resistance in the resistant parent and its progenies and in unrelated maize lines. Downregulation of HA genes causes increased susceptibility to S. hermonthica infestation in loss-of-function maize mutants. While the mechanism of BX action in parasitic plant resistance is yet to be uncovered, the potential of this discovery for developing effective control and breeding strategies is enormous.

Plant small RNAs (sRNAs) are a heterogeneous group of noncoding RNAs with a length of 20–24 nucleotides that are widely studied due to their importance as major regulators in various biological processes. sRNAs are divided into two main classes—microRNAs (miRNAs) and small interfering RNAs (siRNAs)—which differ in their biogenesis and functional pathways. Their identification and enrichment with new structural variants would not be possible without the use of various high-throughput sequencing (NGS) techniques, allowing for the detection of the total population of sRNAs in plants. Classifying sRNAs and predicting their functional role based on such high-performance datasets is a nontrivial bioinformatics task, as plants can generate millions of sRNAs from a variety of biosynthetic pathways. Over the years, many computing tools have been developed to meet this challenge. Here, we review more than 35 tools developed specifically for plant sRNAs over the past few years and explore some of their basic algorithms for performing tasks related to predicting, identifying, categorizing, and quantifying individual sRNAs in plant samples, as well as visualizing the results of these analyzes. We believe that this review will be practical for biologists who want to analyze their plant sRNA datasets but are overwhelmed by the number of tools available, thus answering the basic question of how to choose the right one for a particular study.

Viroid and viroid-like satellite RNAs are infectious, circular, non-protein coding RNAs reported in plants only so far. Some viroids (family Avsunviroidae) and viroid-like satellite RNAs share self-cleaving activity mediated by hammerhead ribozymes (HHRzs) endowed in both RNA polarity strands. Using a homology-independent method based on the search for conserved structural motifs of HHRzs in reads and contigs from high-throughput sequenced RNAseq libraries, we identified a novel small (550 nt) viroid-like RNA in a library from a Citrus reticulata tree. Such a viroid-like RNA contains a HHRz in both polarity strands. Northern blot hybridization assays showed that circular forms of both polarity strands of this RNA (tentatively named citrus transiently-associated hammerhead viroid-like RNA1 (CtaHVd-LR1)) exist, supporting its replication through a symmetric pathway of the rolling circle mechanism. CtaHVd-LR1 adopts a rod-like conformation and has the typical features of quasispecies. Its HHRzs were shown to be active during transcription and in the absence of any protein. CtaHVd-LR1 was not graft-transmissible, and after its first identification, it was not found again in the original citrus source when repeatedly searched in the following years, suggesting that it was actually not directly associated with the plant. Therefore, the possibility that this novel self-cleaving viroid-like RNA is actually associated with another organism (e.g., a fungus), in turn, transiently associated with citrus plants, is proposed.

Despite the importance of storage root (SR) organs for cassava and the other root crops yield, their developmental origin is poorly understood. Here we use multiple approaches to shed light on the initial stages of root development demonstrating that SR and fibrous roots (FR) follow different rhizogenic processes. Transcriptome analysis carried out on roots collected before, during and after root bulking highlighted early and specific activation of a number of functions essential for root swelling and identified root-specific genes able to effectively discriminate emerging FR and SR. Starch and sugars start to accumulate at a higher rate in SR before they swell but only after parenchyma tissue has been produced. Finally, using non-destructive computed tomography measurements, we show that SR (but not FR) contain, since their emergence from the stem, an inner channel structure in continuity with the stem secondary xylem, indicating that SR derive from a distinct rhizogenic process compared with FR.

Earth’s life may have originated as self-replicating RNA. Some of the simplest current RNA replicators are RNA viruses, defined by linear RNA genomes encoding an RNA-dependent RNA polymerase (RdRP), and subviral agents with single-stranded, circular RNA genomes, such as viroids encoding paired self-cleaving ribozymes. Amongst a massive expansion of candidate viroid and viroid-like elements, we report that fungal pathogens, ambiviruses, are viroid-like elements which undergo rolling circle replication and encode their own viral RdRP, thus they are a distinct hybrid infectious agent. These findings point to a deep evolutionary history between modern RNA viruses and sub-viral elements and offer new perspectives on the evolution of primordial infectious agents, and RNA life. One-Sentence Summary Novel infectious agents resembling self-cleaving viroid-like RNAs whilst encoding a viral RNA-dependent RNA polymerase.