Ureteroscopia versus litotripsia extracorpórea con ondas de choque

Potato leaf roll virus (PLRV) belongs to the family Luteoviridae and is a type member of the genus Polerovirus. The icosahedral virions have a diameter of 24 nm that are principally limited to the host phloem cells (DeBlasio et al. 2016; Mayo et al. 2000) and are transmitted persistently by aphid species, predominantly by Myzus persicae Sulz. (Casper, 1988; Syller, 1996). The virus represses translocation of produced carbohydrates resulting in carbohydrate accumulation within the leaves. This leads to upward rolled, leathery and fragile leaf characteristics and phloem necrosis that leads to easy cracking leaflets, if crushed between the fingers (Faccioli et al. 1971). Additionally, the reduced distribution and turnover of primary metabolites often result in stunted host plants (Faccioli et al. 1971; Syller 1996). Further consequences are reduced tuber sizes and tuber yield up to 60% (Hamm and Hane 1999; Loebenstein 2001; McDonald 1976). Secondary infections lead to severe plant stunting and strong upward rolling of basal leaves. Aerial parts of some susceptible potato varieties are capable to show extreme necrosis of phloem tissue and their tubers sometimes display net necrosis symptoms (Douglas and Pavek 1972). The host range is mainly restricted to species of Solanacae, including potato virus indicator plants such as Datura species and Physalis

domestica, Fragaria x ananassa and Prunus species are other PLRV host crop plants (Hühnlein 2016a).

With invention of systemic insecticides in agricultural and horticultural application in the 80ies, the incidence of PLRV decreased remarkably (Hühnlein et al. 2016b; Valkonen 2007) (Dupuis 2017). Before that time, PLRVwas reported as one of the most important viruses in crop potato production(Hühnlein et al. 2016b; Murphy et al. 1966). Depending on the target site, systemic insecticides often induce the death of an aphid before the virus reaches their salivary glands important for persistent virus transmission (Figure 4). However, systemic insecticides neonicotinoids (e.g. imidacloprid, clothianidin, thiamethoxam, dinotefuran, acetamiprid and thiacloprid) are not only destructive to agricultural and horticultural pathogens. Authors consider them as neurotoxic to bees and probably to other non-target invertebrates like forest and meadow insects (Pisa et al. 2015; Lundin et al. 2015). That could be a reason for the European Commission to restrict many broad-spectrum systemic insecticides like the group of neonicotinoids as effective agricultural application in aphid control of potato crop production. According to Hühnlein (2016a) the loss of applicable compounds acting systemically against aphids could lead to insufficient control of aphid vectors in potato crop production and bring a revival of PLRV incidence.

PLRV has a single-stranded positive sense RNA genome of about 5865 nucleotides, which is packed into a non-enveloped icosahedral capsid. The capsid comprises 180 coat protein (CP, P3) subunits with an unknown contingent ratio holding a read-through protein (RTP, P3/P5) extension exposed on the capsid surface (Bahner et al. 1990; Chavez et al. 2012; Peter et al. 2008). The RTP (P3/P5) is translated due to suppression of the coat protein stop codon (Bahner et al. 1990; Mayo et al. 1989). This leads to 80 kDa RTP, containing 23 kDa coat protein domain (P3) and a 57 kDa read-through domain (RTD; P5; Miller and Mayo 1991). The coat protein domain (P3) is essential for the virus encapsulation. PLRV particles with deletions in their read-through proteins are infectious but not aphid transmissible (Peter et al. 2008). Within the RTD (P5) there is a highly conserved N-terminal region, responsible for aphid transmission and aphid endosymbiont interaction and a variable C-terminal region, which is suggested to be dispensable for aphid transmission (van den Heuvel et al. 1997; Wang et al. 1995) but thought to be responsible for phloem limitation of PLRV (Peter et al. 2009). Solanum sarachoides plants infected with PLRV mutant lacking one of two known cross-linking sites in the RTP exhibited a delay in the appearance of systemic infection symptoms (Chavez et al. 2012).

The gRNA of PLRV is directly translated into so far five known proteins, four of them by ribosomal frame shifting (Figure 4; Mayo et al. 1989; ViralZone_PLRV 2017). The first open reading frame is coding for the RNA silencing suppressor (P0, Han et al. 2010), the second one leads to a polyprotein consisting of one proteinase P1 and a viral genome-linked protein

Introduction

(VPg) separated by a self-proteolysis site (Prüfer et al. 1999) and the third open reading frame (P2) codes for the RNA-dependent RNA polymerase (RdRp) that is translated via ribosomal frameshifting at slippery sequence UUUAAAU (Prüfer et al. 1992). The fifth protein is expressed from the ORF starting at about 1500 nucleotides and is termed the replication associated protein (Rap1), which is translated via internal ribosomal entry site (IRES; Jaag et al. 2003). Furthermore, at the 3'-end of the gRNA nucleotide sequence, three positive sense sgRNAs are transcribed and act as templates for translation of so far six known additional proteins (P3, P3a, P4, P5, P6 and P7; Figure 4). The coat protein (P3), P3a, the movement protein (P4) and the read-through domain (P5) are translated from the sgRNA1 (Miller and Mayo 1991; Smirnova et al. 2015; Smith and Harris 1990). Whereas, P3, P3a, P4 and P5 are translated by leaky scanning (Tacke et al. 1990; Smirnova et al. 2015), the sgRNA2 carries two ORFs being separated by small non-coding regions for translation of proteins P6 and P7 (Ashoub et al. 1998) and sgRNA3 serves as template for translation of P7 that was found, lately (Hwang et al. 2013).

In Figure 4, the functions of the PLRV proteins are mentioned. RNA silencing suppression activity was discovered for P0 and P6 proteins of the virus species of Luteoviridae family, Melon aphid-borne yellows virus, Barley yellow dwarf virus and Wheat yellow dwarf virus (Han et al. 2010; Liu et al. 2012). The P1-VPg protein is obligatory for replication (Sadowy et al. 2001). Since it is the main goal of a virus particle to replicate, other PLRV proteins like Replication-associated protein 1 (Rap1; Jaag et al. 2003) and the RNA-dependent RNA polymerase (RdRp, P2; Prüfer et al. 1992) have been found to contribute to replication, as well. The proteins P3a (Smirnova et al. 2015), P3 as coat protein, P4 (Schmitz et al. 1997; Lee et al. 2002; Hofius et al. 2001) and the read-through protein (RTP, P3-P5; Chavez et al. 2012) contribute to cell-to-cell movement and virus transmission.

Figure 4: Genome organization of PLRV (A) persistent aphid transmission (B) and role of proteins (C).

The 5865 nucleotides of the PLRV genome lead to so far ten known proteins. Five of them are translated by ribosomal frame shifting from the gRNA (P0, P1, VPg, P2 and Rap1). The separation of the polyprotein P1-VPg is realized via self- proteolysis, while Rap1 is translated via internal ribosomal entry site (IRES; Jaag et al., 2003). Three positive-sense sgRNAs act as templates for translation of so far six known additional proteins (P3, P3a, P4, P5, P6 and P7). The coat protein (P3), P3a, the movement protein (P4) and the read-through domain (P5) are translated from the sgRNA1. The mechanism behind the overlapping ORFs is leaky scanning and a read-through sequence in case of the read-through protein (RTP, P3-P5). The sgRNA2 serves as template for translation of proteins P6 and P7 and sgRNA3 encodes P7, only. The process of persistent virus transmission by aphids is described based on information of Ali et al. (2014).

Introduction