The plant virus transmissions database

Plant viruses are transmitted mechanically or by vegetative propagation, and by vectors such as arthropods, fungi, nematodes, or parasitic plants. Sources to access available information regarding plant virus transmissions are scattered and require extensive literature searches. Here, a recently created plant virus transmission database is described. This was developed to provide access to the modes of transmission and vectors of over 1600 plant viruses. The database was compiled using over 3500 publication records spanning the last 100 years. The information is publicly accessible via https://library.wur.nl/WebQuery/virus and fully searchable by virus name, taxonomic position, mode of transmission or vector.

Small Talk: On the Possible Role of Trans-Kingdom Small RNAs during Plant-Virus-Vector Tritrophic Communication

Small RNAs (sRNAs) are the hallmark and main effectors of RNA silencing and therefore are involved in major biological processes in plants, such as regulation of gene expression, antiviral defense, and plant genome integrity. The mechanisms of sRNA amplification as well as their mobile nature and rapid generation suggest sRNAs as potential key modulators of intercellular and interspecies communication in plant-pathogen-pest interactions. Plant endogenous sRNAs can act in cis to regulate plant innate immunity against pathogens, or in trans to silence pathogens' messenger RNAs (mRNAs) and impair virulence. Likewise, pathogen-derived sRNAs can act in cis to regulate expression of their own genes and increase virulence towards a plant host, or in trans to silence plant mRNAs and interfere with host defense. In plant viral diseases, virus infection alters the composition and abundance of sRNAs in plant cells, not only by triggering and interfering with the plant RNA silencing antiviral response, which accumulates virus-derived small interfering RNAs (vsiRNAs), but also by modulating plant endogenous sRNAs. Here, we review the current knowledge on the nature and activity of virus-responsive sRNAs during virus-plant interactions and discuss their role in trans-kingdom modulation of virus vectors for the benefit of virus dissemination.

Rescue of Citrus sudden death-associated virus in Nicotiana benthamiana plants from cloned cDNA: insights into mechanisms of expression of the three capsid proteins

Citrus sudden death-associated virus (CSDaV) is a member of the genus Marafivirus in the family Tymoviridae, and has been associated with citrus sudden death (CSD) disease in Brazil. Difficulties in the purification of CSDaV from infected citrus plants have prevented progress in the investigation of the role of this virus in CSD and an understanding of its molecular biology. In this work, we have constructed a full-length cDNA clone of CSDaV driven by the 35S promoter (35SRbz-CSDaV). Agrobacterium tumefaciens-mediated inoculation of 35SRbz-CSDaV in Nicotiana benthamiana plants enabled a fast recovery of large amounts of virions from the agroinfiltrated leaves, which allowed a better molecular characterization of CSDaV. In vivo analyses of mutant versions of 35SRbz-CSDaV revealed the expression strategies used by CSDaV for production of the capsid proteins (CPs). We showed that CSDaV virions contain three forms of CP, each of which is generated from the same coding sequence, but by different mechanisms. The major CPp21 is a product of direct translation by leaky scanning from the second start codon in the subgenomic RNA (sgRNA), whereas the minor CPs, p25 and p23, are produced by direct translation from the first start codon in the sgRNA and by trans-proteolytic cleavage processing derived from the p25 precursor, respectively. Together, these findings contribute to advance our understanding of CSDaV genome expression strategies. In addition, the construction and characterization of the CSDaV infectious clone represent important steps towards the investigation of the role of this virus in CSD and of its use as a tool for citrus biotechnology.

Deep Sequencing Analysis of RNAs from Citrus Plants Grown in a Citrus Sudden Death-Affected Area Reveals Diverse Known and Putative Novel Viruses

Citrus sudden death (CSD) has caused the death of approximately four million orange trees in a very important citrus region in Brazil. Although its etiology is still not completely clear, symptoms and distribution of affected plants indicate a viral disease. In a search for viruses associated with CSD, we have performed a comparative high-throughput sequencing analysis of the transcriptome and small RNAs from CSD-symptomatic and -asymptomatic plants using the Illumina platform. The data revealed mixed infections that included Citrus tristeza virus (CTV) as the most predominant virus, followed by the Citrus sudden death-associated virus (CSDaV), Citrus endogenous pararetrovirus (CitPRV) and two putative novel viruses tentatively named Citrus jingmen-like virus (CJLV), and Citrus virga-like virus (CVLV). The deep sequencing analyses were sensitive enough to differentiate two genotypes of both viruses previously associated with CSD-affected plants: CTV and CSDaV. Our data also showed a putative association of the CSD-symptomatic plants with a specific CSDaV genotype and a likely association with CitPRV as well, whereas the two putative novel viruses showed to be more associated with CSD-asymptomatic plants. This is the first high-throughput sequencing-based study of the viral sequences present in CSD-affected citrus plants, and generated valuable information for further CSD studies.