scholarly journals Kinship networks of seed exchange shape spatial patterns of plant virus diversity

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Marc Delêtre ◽  
Jean-Michel Lett ◽  
Ronan Sulpice ◽  
Charles Spillane
Keyword(s):  
Genetic Structure ◽  
Plant Virus ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Seed Systems ◽  
Germplasm Exchange ◽  
Local Networks ◽  
Local Modes ◽  
Seed Exchange ◽  
Virus Diversity

AbstractBy structuring farmers’ informal networks of seed exchange, kinship systems play a key role in the dynamics of crop genetic diversity in smallholder farming systems. However, because many crop diseases are propagated through infected germplasm, local seed systems can also facilitate the dissemination of seedborne pathogens. Here, we investigate how the interplay of kinship systems and local networks of germplasm exchange influences the metapopulation dynamics of viruses responsible for the cassava mosaic disease (CMD), a major threat to food security in Africa. Combining anthropological, genetic and plant epidemiological data, we analyzed the genetic structure of local populations of the African cassava mosaic virus (ACMV), one of the main causal agents of CMD. Results reveal contrasted patterns of viral diversity in patrilineal and matrilineal communities, consistent with local modes of seed exchange. Our results demonstrate that plant virus ecosystems have also a cultural component and that social factors that shape regional seed exchange networks influence the genetic structure of plant virus populations.

scholarly journals Genetic diversity and phylogeography of cassava mosaic viruses in Kenya

2006 ◽  
Vol 87 (10) ◽  
pp. 3053-3065 ◽  
Author(s):  
Simon E. Bull ◽  
Rob W. Briddon ◽  
William S. Sserubombwe ◽  
Kahiu Ngugi ◽  
Peter G. Markham ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Central Africa ◽  
Mosaic Disease ◽  
Sub Saharan Africa ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Polymorphism Analysis ◽  
Virus Species ◽  
East African ◽  
Virus Diversity

Cassava is a major factor in food security across sub-Saharan Africa. However, the crop is susceptible to losses due to biotic stresses, in particular to viruses of the genus Begomovirus (family Geminiviridae) that cause cassava mosaic disease (CMD). During the 1990s, an epidemic of CMD severely hindered cassava production across eastern and central Africa. A significant influence on the appearance of virus epidemics is virus diversity. Here, a survey of the genetic diversity of CMD-associated begomoviruses across the major cassava-growing areas of Kenya is described. Because an initial PCR-restriction fragment-length polymorphism analysis identified a much greater diversity of viruses than assumed previously, representative members of the population were characterized by sequence analysis. The full-length sequences of 109 components (68 DNA-A and 41 DNA-B) were determined, representing isolates of East African cassava mosaic virus and East African cassava mosaic Zanzibar virus, as well as a novel begomovirus species for which the name East African cassava mosaic Kenya virus is proposed. The DNA-B components were much less diverse than their corresponding DNA-A components, but nonetheless segregated into western and eastern (coastal) groups. All virus species and strains encountered showed distinct geographical distributions, highlighting the importance of preventing both the movement of viruses between these regions and the importation of the disease from adjacent countries and islands in the Indian Ocean that would undoubtedly encourage further diversification.

scholarly journals WRKY Transcription Factors in Cassava Contribute to Regulation of Tolerance and Susceptibility to Cassava Mosaic Disease through Stress Responses

Viruses ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1820
Author(s):  
Warren Freeborough ◽  
Nikki Gentle ◽  
Marie E. C. Rey
Keyword(s):  
Transcription Factors ◽  
Stress Responses ◽  
Regulatory Networks ◽  
Large Scale ◽  
Mosaic Disease ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Manihot Esculenta Crantz ◽  
Transcriptional Reprogramming ◽  
Negative Role

Among the numerous biological constraints that hinder cassava (Manihot esculenta Crantz) production, foremost is cassava mosaic disease (CMD) caused by virus members of the family Geminiviridae, genus Begomovirus. The mechanisms of CMD tolerance and susceptibility are not fully understood; however, CMD susceptible T200 and tolerant TME3 cassava landraces have been shown to exhibit different large-scale transcriptional reprogramming in response to South African cassava mosaic virus (SACMV). Recent identification of 85 MeWRKY transcription factors in cassava demonstrated high orthology with those in Arabidopsis, however, little is known about their roles in virus responses in this non-model crop. Significant differences in MeWRKY expression and regulatory networks between the T200 and TME3 landraces were demonstrated. Overall, WRKY expression and associated hormone and enriched biological processes in both landraces reflect oxidative and other biotic stress responses to SACMV. Notably, MeWRKY11 and MeWRKY81 were uniquely up and downregulated at 12 and 67 days post infection (dpi) respectively in TME3, implicating a role in tolerance and symptom recovery. AtWRKY28 and AtWRKY40 homologs of MeWRKY81 and MeWRKY11, respectively, have been shown to be involved in regulation of jasmonic and salicylic acid signaling in Arabidopsis. AtWRKY28 is an interactor in the RPW8-NBS resistance (R) protein network and downregulation of its homolog MeWRKY81 at 67 dpi in TME3 suggests a negative role for this WRKY in SACMV tolerance. In contrast, in T200, nine MeWRKYs were differentially expressed from early (12 dpi), middle (32 dpi) to late (67 dpi) infection. MeWRKY27 (homolog AtWRKY33) and MeWRKY55 (homolog AtWRKY53) were uniquely up-regulated at 12, 32 and 67 dpi in T200. AtWRKY33 and AtWRKY53 are positive regulators of leaf senescence and oxidative stress in Arabidopsis, suggesting MeWRKY55 and 27 contribute to susceptibility in T200.

Plant Virus Diversity and Evolution

2016 ◽  
pp. 197-215 ◽  
Author(s):  
Anthony Stobbe ◽  
Marilyn J. Roossinck
Keyword(s):  
Plant Virus ◽  
Virus Diversity

scholarly journals Agrobacterium-Mediated Gene Transient Overexpression and Tobacco Rattle Virus (TRV)-Based Gene Silencing in Cassava

2019 ◽  
Vol 20 (16) ◽  
pp. 3976 ◽  
Author(s):  
Hongqiu Zeng ◽  
Yanwei Xie ◽  
Guoyin Liu ◽  
Yunxie Wei ◽  
Wei Hu ◽  
...  
Keyword(s):  
Gene Silencing ◽  
Functional Genomics ◽  
Transient Expression ◽  
Fluorescent Protein ◽  
Tobacco Rattle Virus ◽  
Mosaic Disease ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Virus Induced Gene Silencing ◽  
Transient Expression Assay

Agrobacterium-mediated transient expression and virus-induced gene silencing (VIGS) are very useful in functional genomics in plants. However, whether these methods are effective in cassava (Manihot esculenta), one of the most important tropical crops, remains elusive. In this study, we used green fluorescent protein (GFP) and β-glucuronidase (GUS) as reporter genes in a transient expression assay. GFP or GUS could be detected in the infiltrated leaves at 2 days postinfiltration (dpi) and were evidenced by visual GFP and GUS assays, reverse-transcription PCR, and Western blot. In addition, phytoene desaturase (PDS) was used to show the silencing effect in a VIGS system. Both Agrobacterium GV3101 and AGL-1 with tobacco rattle virus (TRV)-MePDS-infiltrated distal leaves showed an albino phenotype at 20 dpi; in particular, the AGL-1-infiltrated plants showed an obvious albino area in the most distal leaves. Moreover, the silencing effect was validated by molecular identification. Notably, compared with the obvious cassava mosaic disease symptom infiltrated by African-cassava-mosaic-virus-based VIGS systems in previous studies, TRV-based VIGS-system-infiltrated cassava plants did not show obvious virus-induced disease symptoms, suggesting a significant advantage. Taken together, these methods could promote functional genomics in cassava.

scholarly journals Variants of East African cassava mosaic virus and Its Distribution in Double Infections with African cassava mosaic virus in Nigeria

Plant Disease ◽  
2003 ◽  
Vol 87 (3) ◽  
pp. 229-232 ◽  
Author(s):  
F. O. Ogbe ◽  
G. Thottappilly ◽  
A. G. O. Dixon ◽  
G. I. Atiri ◽  
H. D. Mignouna
Keyword(s):  
Mosaic Virus ◽  
Mosaic Disease ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Single Infection ◽  
East African ◽  
Humid Forest ◽  
Forest Region ◽  
Agroecological Zones ◽  
Cassava Mosaic Virus

In a survey for cassava mosaic begomoviruses conducted in 1997 and 1998 in Nigeria, East African cassava mosaic virus (EACMV) was detected by the polymerase chain reaction together with African cassava mosaic virus (ACMV) in 27 out of 290 cassava leaf samples of infected plants from 254 farmers' fields in five agroecological zones. One plant was infected with EACMV only. Five variant isolates of EACMV were observed based on their reactions to primers that could detect Cameroonian and East African strains of EACMV. Isolates of variants 1 and 3 occurred mostly in the derived or coastal and southern Guinea savannahs, while variants 4 and 5 predominated in the humid forest region. Isolates of variant 2 were widely distributed across the three agroecologies. EACMV was not detected in the northern Guinea savannah and arid and semiarid zones. Most doubly infected plants showed more severe symptoms than plants with single infection. Occurrence of EACMV variants together with ACMV detection and information about their distribution in Nigeria could be used for the selection of cassava clones in cassava mosaic disease resistance programs.

scholarly journals Recombination, pseudorecombination and synergism of geminiviruses are determinant keys to the epidemic of severe cassava mosaic disease in Uganda

2001 ◽  
Vol 82 (3) ◽  
pp. 655-665 ◽  
Author(s):  
J. S. Pita ◽  
V. N. Fondong ◽  
A. Sangaré ◽  
G. W. Otim-Nape ◽  
S. Ogwal ◽  
...  
Keyword(s):  
Mosaic Virus ◽  
Mosaic Disease ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
East African ◽  
Recombinant Fragment ◽  
Complete Sequences ◽  
Natural Recombination ◽  
Cassava Mosaic Virus

The molecular variability of cassava geminiviruses occurring in Uganda was investigated in this study. Infected cassava plants and whiteflies were collected from cassava plantings in different geographical areas of the country and PCR was used for molecular characterization of the viruses. Two complete sequences of DNA-A and -B from African cassava mosaic virus (ACMV), two DNA-A sequences from East African cassava mosaic virus (EACMV), two DNA-B sequences of EACMV and the partial DNA-A nucleotide sequence of a new virus strain isolated in Uganda, EACMV-UG3, are reported here. Analysis of naturally infected cassava plants showed various assortments of DNA-A and DNA-B of the Ugandan viruses, suggesting the occurrence of natural inter- and intraspecies pseudorecombinations and a pattern of cassava mosaic disease (CMD) more complex than previously reported. EACMV-UG2 DNA-A, which contains a recombinant fragment between ACMV and EACMV-UG1 in the coat protein gene that resembles virus from Tanzania, was widespread in the country and always associated with EACMV-UG3 DNA-B, which probably resulted from another natural recombination event. Mixed infections of ACMV-UG and EACMV-UG in cassava and whiteflies were detected in most of the regions where both viruses occurred. These mixed-infected samples always showed extremely severe CMD symptoms, suggesting a synergistic interaction between ACMV-UG and EACMV-UG2. The first demonstration is provided of infectivity of EACMV clones to cassava, proving conclusively that the pseudorecombinant EACMV-UG2 DNA-A+EACMV-UG3 DNA-B is a causal agent of CMD in Uganda.

scholarly journals First Report of the Presence of East African Cassava Mosaic Virus in Cameroon

Plant Disease ◽  
1998 ◽  
Vol 82 (10) ◽  
pp. 1172-1172 ◽  
Author(s):  
V. N. Fondong ◽  
J. S. Pita ◽  
C. Rey ◽  
R. N. Beachy ◽  
C. M. Fauquet
Keyword(s):  
Mosaic Virus ◽  
East Africa ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Symptom Expression ◽  
Virus Species ◽  
East African ◽  
First Report ◽  
Sequence Identity ◽  
Cassava Mosaic Virus

Cassava mosaic disease (CMD) occurs in all cassava-growing regions of Africa, India, and Sri Lanka. Characterized by mosaic and distortion of cassava leaves and reduced plant growth, causing high yield losses, CMD is caused by geminiviruses (genus Begomovirus, family Geminiviridae) transmitted through infected cuttings or by the whitefly, Bemisia tabaci. Three such geminiviruses have been described: African cassava mosaic virus (ACMV) occurs in most of the cassava-producing zones of Africa; East African cassava mosaic virus (EACMV) in East Africa; and Indian cassava mosaic virus (ICMV) in the Indian subcontinent (1). The two components of ACMV and ICMV genomes, DNA-A and DNA-B, have been sequenced; only DNA-A of EACMV has been identified and sequenced. Variations in symptom expression and severity within the same cassava variety have been observed in Cameroon. To determine the nature of the virus species inducing such variations, 50 samples were collected from CMD-infected plants in the savannah and rainforest zones of Cameroon: 2 from the sahel/savannah plain, 13 from the western highland savannah, and 35 from the main cassava-producing belt of the southwestern rainforest. There is a high incidence of CMD in the rainforest region, with some farms completely infected, while in the savannah regions farms generally have less than 25% incidence. Variation in symptom expression was more common in the rainforest region. Samples were collected from plants with distinct symptoms and/or different extents of symptom severity, then analyzed with the polymerase chain reaction (PCR) with specific primers: JSP1, ATG TCG AAG CGA CCA GGA GAT; JSP2, TGT TTA TTA ATT GCC AAT ACT; and JSP3, CCT TTA TTA ATT TGT CAC TGC. Primer JSP1 anneals to the 5′ end of the coat protein (CP) of ACMV and EACMV; primers JSP2 and JSP3 anneal to the 3′ ends of ACMV and EACMV, respectively. Virus identification was based on presence of an amplified fragment of either virus. ACMV was detected in all 50 samples; EACMV was detected in 8. All samples infected with EACMV were from the southwestern rainforest of Cameroon and were more severely affected by the disease than single infected plants. Previous reports have limited occurrence of EACMV to East Africa (1). This is the first report of the occurrence of EACMV in West Africa. The CP gene of three isolates of EACMV from Cameroon (EACMV/CM) was sequenced from cloned PCR products. There was a high CP nucleotide sequence identity (>99%) with only two amino acid differences among all three EACMV isolates. In contrast, there was a rather low sequence identity (94%) with EACMV/TZ from Tanzania (2), suggesting they may belong to a previously undescribed West African strain of EACMV. This indicates the geminiviruses causing CMD in Africa are more widely distributed than previously reported. None of the Cameroon isolates showed the type of recombination of the EACMV isolate from Uganda (EACMV/ UG) (having the CP core segment the identical to the corresponding ACMV CP sequence) (2). This emphasizes the need for characterization of the viruses causing CMD in different cassava-growing regions of Africa since appropriate control strategies depend on adequate knowledge of disease etiology. References: (1) Y. G. Hong et al. J. Gen. Virol. 74:2437, 1993. (2) X. Zhou et al. J. Gen. Virol. 78:2101, 1997.

scholarly journals Validation of high rates of nucleotide substitution in geminiviruses: phylogenetic evidence from East African cassava mosaic viruses

2009 ◽  
Vol 90 (6) ◽  
pp. 1539-1547 ◽  
Author(s):  
Siobain Duffy ◽  
Edward C. Holmes
Keyword(s):  
Nucleotide Substitution ◽  
Central Africa ◽  
Mosaic Disease ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
East African ◽  
Substitution Rates ◽  
Leaf Curl Virus ◽  
Intensive Sampling ◽  
Major Pathogens

Whitefly-transmitted geminiviruses are major pathogens of the important crop cassava in Africa. The intensive sampling and sequencing of cassava mosaic disease-causing viruses that occurred in the wake of a severe outbreak in Central Africa (1997–2002) allowed us to estimate the rate of evolution of this virus. East African cassava mosaic virus and related species are obligately bipartite (DNA-A and DNA-B segments), and these two genome segments have different evolutionary histories. Despite these phylogenetic differences, we inferred high rates of nucleotide substitution in both segments: mean rates of 1.60×10−3 and 1.33×10−4 substitutions site−1 year−1 for DNA-A and DNA-B, respectively. While similarly high substitution rates were found in datasets free of detectable recombination, only that estimated for the coat protein gene (AV1), for which an additional DNA-A sequence isolated in 1995 was available, was statistically robust. These high substitution rates also confirm that those previously estimated for the monopartite tomato yellow leaf curl virus (TYLCV) are representative of multiple begomoviruses. We also validated our rate estimates by comparing them with those depicting the emergence of TYLCV in North America. These results further support the notion that geminiviruses evolve as rapidly as many RNA viruses.

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