Light-dependent segregation of begomoviruses in Asystasia gangetica leaves

Emergence of begomoviruses and DNA satellites associated with weeds and intercrops: a potential threat to sustainable production of cassava in Côte d'Ivoire

Cassava (Manihot esculenta Crantz) plays a significant role in the livelihoods of people in Africa, particularly in Côte d'Ivoire. However, its production is threatened by begomoviruses which cause huge yield losses. Some weeds and food crops intercropped with cassava act as reservoirs, thereby facilitating the sustenance and propagation of Cassava mosaic begomoviruses (CMBs), along with other begomoviruses. To effectively manage these diseases, it is imperative to enhance our understanding of the various hosts of cassava viruses in Côte d'Ivoire. Thus, a comprehensive nationwide survey was conducted in 2017 in cassava fields across Côte d'Ivoire, and molecular analyses were performed on the samples collected. The results obtained from this survey indicated that 65 plant species belonging to 31 families were potential alternative hosts for CMBs in Côte d'Ivoire. The molecular analyses revealed that four species, Capsicum annuum, Solanum melongena, Centrosema pubescens, and Asystasia gangetica exhibited differential affinities for both African cassava mosaic virus and East African cassava mosaic Cameroon virus. Additionally, other begomoviruses and new alphasatellites were identified. Soybean chlorotic blotch virus was isolated from C. pubescens while West African Asystasia virus 1, West African Asystasia virus 2, and a new Asystasia yellow mosaic alphasatellite were isolated from A. gangetica which appears to be a plant species that could favor the emergence of new viral species harmful to cassava cultivation. This study offers insights that will inform the development of more effective control methods for sustainable cassava production in Côte d'Ivoire.

C4, the Pathogenic Determinant of Tomato Leaf Curl Guangdong Virus, May Suppress Post-transcriptional Gene Silencing by Interacting With BAM1 Protein

Tomato leaf curl Guangdong virus (ToLCGdV) is a begomovirus associated with a Tomato yellow leaf curl disease (TYLCD) epidemic in Guangdong province, China. Being the least conserved protein among geminivirus proteins, the function of C4 during ToLCGdV infection has not been elucidated. In this study, the infectious clones of ToLCGdV and a ToLCGdV mutant (ToLCGdV_mC4) with disrupted C4 ORF were constructed. Although ToLCGdV and ToLCGdV_mC4 could infect Nicotiana benthamiana and tomato plants, ToLCGdV_mC4 elicited much milder symptoms compared with ToLCGdV. To further verify the role of C4 in viral pathogenesis, C4 was expressed in N. benthamiana from Potato virus X (PVX) vector. The results showed that ToLCGdV C4 enhanced the pathogenicity of PVX and induced more severe developmental abnormalities in plants compared with PVX alone or PVX-mC4. In addition, ToLCGdV C4 suppresses systemic gene silencing in the transgenic N. benthamiana line 16c, but not local gene silencing induced by sense GFP in wild-type N. benthamiana plants. Moreover, C4 suppresses transcriptional gene silencing (TGS) by reducing the DNA methylation level of 35S promoter in 16c-TGS N. benthamiana plants. Furthermore, C4 could also interact with the receptor-like kinase (RLK) BARELY ANY MERISTEM 1 (BAM1), suggesting that C4 may suppress gene silencing by interfering with the function of BAM1 in the cell-to-cell spread of RNAi. All these results suggest that C4 is a pathogenic determinant of ToLCGdV, and C4 may suppress post-transcriptional gene silencing (PTGS) by interacting with BAM1.

Barcoding of Plant Viruses with Circular Single-Stranded DNA Based on Rolling Circle Amplification

The experience with a diagnostic technology based on rolling circle amplification (RCA), restriction fragment length polymorphism (RFLP) analyses, and direct or deep sequencing (Circomics) over the past 15 years is surveyed for the plant infecting geminiviruses, nanoviruses and associated satellite DNAs, which have had increasing impact on agricultural and horticultural losses due to global transportation and recombination-aided diversification. Current state methods for quarantine measures are described to identify individual DNA components with great accuracy and to recognize the crucial role of the molecular viral population structure as an important factor for sustainable plant protection.

Complete genome sequence of a new bipartite begomovirus infecting cotton in the Republic of Benin in West Africa

Here, we report the complete genome sequence of a novel bipartite begomovirus isolated from cotton plants (Gossypium raimondii, Malvaceae) exhibiting light yellow mosaic symptoms. The genome sequence was determined by Illumina DNA sequencing and confirmed by Sanger sequencing of RCA-enriched, cloned circular genomic components. The DNA-A and DNA-B components were each ~2.7 kb in size, and their genome arrangement was characteristic of other Old World bipartite begomoviruses. While the DNA-A component was most closely related to tobacco leaf curl Comoros virus (TbLCKMV) at 80 %, the DNA-B component had as its closet relative soybean chlorotic blotch virus (SbCBV) at 66 %. This previously undescribed begomovirus is herein named "cotton yellow mosaic virus" (CYMV).