Value of clay as a supplement to swine diets

Daye Mun1Jongmoon Lee1Jeehwan Choe1Byeonghyeon Kim1Sangnam Oh2*Minho Song1*

Abstract

The use of practical management factors to maximize pig health improvement cannot guarantee freedom from diseases. Moreover, because of health safety concerns, the use of antibiotics has been restricted in livestock, including pigs. Therefore, the swine industry has been looking for various alternatives to antibiotics to improve pig’s health and performance. Clay is a dietary factor generally accepted for improving pig health. It is a naturally occurring material and is primarily composed of fine-grained minerals. It has a specific structure with polar attraction. Because of this structure, clay has the ability to lose or gain water reversibly. In addition, clay has beneficial physiological activities. First, clay has anti-diarrheic and antibacterial effects by penetrating the cell wall of bacteria or inhibiting their metabolism. Second, it can protect the intestinal tract by absorbing toxins, bacteria, or even viruses. When added to the diet, clay has also been known to bind some mycotoxins, which are toxic secondary metabolites produced by fungi, namely in cereal grains. Those beneficial effects of clay can improve pigs’ health and performance by reducing pathogenic bacteria, especially pathogenic Escherichia coli, in the intestinal tract. Therefore, it is suggested that clay has a remarkable potential as an antibiotics alternative.

Keyword



Introduction

An important management point in the swine industry is to maximize pig health improvement to keep pigs free of various diseases. The most practical management factors are follows: all-in/all-out pig flow, age segregation, intense biosecurity practices, sanitation, new vaccinations, and depopulation/repopulation (Hardy, 2002; Adjiri-Awere and van Lunen, 2005). However, these techniques cannot guarantee freedom from diseases for pigs although they are common and widely used. Thus, it is necessary to apply other methods to support these limited technologies.

The use of antibiotics is one of the most effective ways to prevent diseases in any livestock, including pigs (Jang et al., 2016). However, it has been reported that the use of antibiotics in the

swine industry has potential safety issues, such as the emergence of antibiotic-resistant enteric bacteria which cause a high risk to both animal and human health (Cromwell, 2002; Hardy, 2002). Due to these health safety issues, most countries have restricted antibiotics use, forcing the swine industry to find alternatives to antibiotics to improve pig health without safety issues.

Dietary factors (e.g., feed ingredients, feed additives, or feeding methods) have been increasingly considered for the improvement of pigs’ health and performance (Pluske et al., 2002; Stein and Kil, 2006; Park et al., 2016). Moreover, it is generally accepted that some dietary factors, such as clay, spray-dried plasma, and enzymes, are important nutrient sources and can improve pig health. Some literature reported that these factors provide physiological activities such as the modulation of the intestinal environment and absorption properties which affect pathogenic microbes directly or indirectly (Song et al., 2012, Jang et al., 2016). This implies that dietary factors can be an effective component of swine health management programs along with existing practical management practices. This article reviews the value of dietary factors with a focus on the value of clay supplement.

Character of Clay and Utilization in Swine Diets

Definition and Structure of Clay

“The term ‘clay’ refers to a naturally occurring materials, found in geological deposits, which is composed primarily of fine-grained minerals (< 2.0 µm in diameter) such as, phyllosilicate and other minerals. These impart plasticity to clay as variable amounts of water are trapped in the mineral structure by polar attraction. Clay will harden when dried or fired” (Guggenheim and Martin, 1995; Williams et al., 2009).

Natural clay deposits are rarely pure and most of them contain mixtures of a variety of minerals from various clay mineral groups such as kaolinite, montmorillonite-smectite, illite, and chlorite (Williams et al., 2009). Three different structures exist: 1) 1 : 1 layer structure formed between a single octahedral sheet ((Al, Mg, Fe)O6) and a single tetrahedral sheet ((Al, Si)O4), 2) 2 : 1 layer structure formed from sandwiching a single octahedral sheet ((Al, Mg, Fe)O6) between two tetrahedral sheets ((Al, Si)O4), and 3) framework structure that is a three dimensional frameworks of SiO44- and AlO45- tetrahedra linked through shared oxygen atoms (Papaioannou et al., 2005; Williams and Haydel, 2010).

General Effects and Proposed Mechanisms of Clay

Clays have several potential effects when they are administered orally or topically (Carretero, 2002; Gomes and Silva, 2007; Tateo and Summa, 2007). For oral applications, first, clays are used as gastrointestinal protectors, especially palygorskites or kaolinites. The gastric and intestinal mucous membranes can be protected as clays adhere to them and absorb toxins, bacteria, or even viruses, but they also eliminate enzymes or other nutritive elements. Second, clays, especially sodium smectites, are used as osmotic laxatives to encourage defecation. This is not a function of the clay itself but of the interlayered Na+ as it spreads and produces the osmotic pressure in the intestines. Third, clays are used as antidiarrheics, especially clays with absorbent minerals such as kaolinites, palygorskites, or calcium smectites, which have a high capacity for water absorption. They work by reducing the quantity of liquid and the speed of passage through the intestines as clays absorb excess water as well as gases in the digestive tract. Fourth, clays have potential antibacterial (bacteriostatic or bactericidal) effects by penetrating the cell wall of bacteria or inhibiting their metabolisms.

There are two types of proposed mechanisms, physical and chemical means (Papaioannou et al., 2005; Williams et al., 2009). As an example of physical means, clays are hydrophilic or organophilic. Organophilic smectities (modified clays), made by inserting alkylammonium compounds into the clay interlayer, can attract the bacterial cell to the surface of the clay with enough physical force that the cell membrane is torn (adsorption property), causing bacterial cell death (Papaioannou et al., 2005; Williams et al., 2009). Natural clays also have this same effect of bacterial cell lysis by physical force. This adsorption property combined with the physical force of clays may be beneficial for killing bacteria. However, clays may harm host tissues because they can also adhere to gastrointestinal walls and modify or reinforce the mucus lining of intestines (Tateo and Summa, 2007).

 As an example of chemical means, French green clays used for treating Buruli ulcer caused by Mycobacterium ulcerans are dominated by illite and Fe-smectite mineralogically, which are hydrophilic (Papaioannou et al., 2005; Williams et al., 2008). These natural clays may have potential effects that kill bacteria with chemical exchanges in aqueous media by providing a toxin to bacteria, depriving bacteria of essential nutrients for their metabolism, or changing pH and oxidation state in the intestines. There are also other clay effects such as dermatological protection, excipients for drug, pelotherapy, etc., but only oral application cases are considered in this review.

Physiological Effects of Clays

Clays as a Mycotoxin Binder

Mycotoxins (aflatoxin, ergot alkaloids, fumonisin, orchartoxin, vomitoxin, or zearalenone) are the toxic secondary metabolites produced by fungi (Aspergillus, Fusarium, Penicillium, and Claviceps species) in cereal grains during storage, growth, harvest, transportation, or processing (Lindemann et al., 1993). These mycotoxins are detrimental to animal growth, production, and health when animals consume diets contaminated with them. A practical approach has been the addition of adsorbents to contaminated feed to bind the mycotoxins and to reduce the detrimental effects by mycotoxins. One solution may be the addition of clays in livestock diets. A hydrated sodium calcium aluminosilicate (HSCAS, clay) has been known to bind some of these mycotoxins when added to the livestock diets (Phillips et al., 1988; Papaioannou et al., 2005). In vitro studies showed the adsorption of mycotoxins by clays (Lemke et al., 1998; Lemke et al., 2001). In vivo studies showed that the addition of clays in the pig diets reduce the adverse effects of aflatoxin in the diets on growth rate and serum indicators of protein synthetic capabilities and of liver damage of pigs (Lindemann et al. 1993; Schell et al., 1993a; Schell et al., 1993b).

Effects of Clay on Pig Performance

Field observations suggest that clays in pig diets also have anti-toxic or -diarrheic effects. Without challenge, clays may improve (Pond et al., 1988; Papaioannou et al., 2004; Alexopoulos et al., 2007; Table 1) or may not improve (Ward et al., 1991; Poulsen and Oksbjerg, 1995; Parisini et al., 1999) the growth rate of pigs. This may be because the ion exchange, adsorption, and catalytic properties of clays may reduce the passage rate through intestinal tract, reduce the enzymatic hydrolysis of diets, and reduce absorption of nutrients (Shurson et al., 1984; Pond et al., 1988). Clays may not affect serum minerals (Papaioannou et al., 2002; Alexopoulos et al., 2007), or may affect them, because of ion exchange properties of clays or interference of mineral ions (e.g., Al) from degradation of clays in the acidic environment (Shurson et al., 1984; Ward et al., 1991). Clays may reduce serum urea nitrogen (Shurson et al., 1984; Poulsen and Oksbjerg, 1995; Alexopoulos et al., 2007) or toxic compounds (Shurson et al., 1984; Ramu et al., 1997) because of the high affinity of clays for ammonium ions, resulting from the deamination of proteins, and for toxic compounds, resulting from microbial degradation. Clays may affect or may not affect (Alexopoulos et al., 2007) hematological parameters such as hematocrit, white blood cell count, and hemoglobin concentrations because of intestinal irritation or inflammation by clays.

Table 1. Effects of clay on pig performance (adapted from Song et al., 2012). http://dam.zipot.com:8080/sites/kjoas/images/N0030440202/Table_KJAOS_44_02_02_T1.jpg

Effects of Clay on Pigs’ Health

Clays reduce piglets’ diarrhea (Stojic et al., 1998; Papaioannou et al., 2004; Fig. 1) after weaning, maybe because of antibacterial effects by clays’ adsorption properties. Trckova et al. (2009) reported, in pigs, that, with a pathogenic E. coli challenge, the clay treatment improves body weight gain (but not growth efficiency), reduces the colonization and shedding of pathogenic E. coli, and does not change hematological parameters of serum or histopathological features of mucosa in small and large intestines compared with pigs fed the control diet.

Fig. 1.

Effect of clay on frequency of diarrhea of pigs (adapted from Song et al., 2012).

http://dam.zipot.com:8080/sites/kjoas/images/N0030440202/Figure_KJAOS_44_02_02_F1.jpg

In addition, some in vitro studies and human research support the antibacterial and mycotoxin binding effects of clays. Ramu et al. (1997) showed that clays adsorb and inactivate the heat-labile (LT) enterotoxins of E. coli and the cholera enterotoxins (CT) of Vibrio cholerae. Some reports showed clays eliminate or inhibit growth of pathogenic E. coli (Tong et al., 2005; Hu and Xia, 2006; Haydel et al., 2008), Salmonella choleraesuis (Tong et al., 2005), and other antibiotic-susceptible and antibiotic-resistant bacteria (Haydel et al., 2008) by damaging bacterial cell wall causing leakage of bacterial enzymes, by inhibiting bacterial respiratory metabolism, or by changing chemical conditions such as pH and oxidation state. Also, in vivo studies of human health showed evidences of those benefits. Some reports showed that clays attenuate overall disorder of diarrhea-predominant irritable bowel syndrome and abdominal pain, discomfort intensity (Chang et al., 2007), and severity of acute diarrhea of children (Madkour et al., 1993; Dupont et al., 2009). In addition, clay may reduce exposure and adverse effects of mycotoxin-contaminated food for humans (Wang et al., 2005).

In vitro studies have shown antiviral effects of clays. Some reports showed clays adsorb rotavirus and coronavirus (Clark et al., 1998), which generally cause gastroenteritis (acute diarrheal disease), and reovirus (Lipson and Stotzky, 1983), which causes gastrointestinal and respiratory problems, with high affinity by physical forces such as van der Waals forces and hydrogen bonding and by formation of a cation bridge between clays and viruses, although the clay-virus complex retained infectivity.

Conclusion

Clay is a naturally occurring material and is composed primarily of fine-grained minerals (phyllosilicate minerals). It has a specific structure which has the ability to lose or gain water reversibly to adsorb molecules and to exchange ions. Based on these properties, we conclude that there are several beneficial physiological activities such as protection of the intestinal tract, anti-diarrheic and antibacterial effects, etc. Those beneficial effects can contribute to improvement of pig performance and health by reducing pathogenic bacteria in the intestinal digestive tract (modulation of microbiota), especially pathogenic E. coli that cause piglets’ diarrhea after weaning.

Acknowledgements

This work was financially supported by the research fund of Chungnam National University in 2015.

References

1 Abbink TE, Peart JR, Mos TN, Baulcombe DC, Bol JF, Linthorst HJ. 2002. Silencing of a gene encoding a protein component of the oxygen-evolving complex of photosystem II enhances virus replication in plants. Virology 295:307-319. 

2 Avesani L, Marconi G, Morandini F, Albertini E, Bruschetta M, Bortesi L, Pezzotti M, Porceddu A. 2007. Stability of Potato virus X expression vectors is related to insert size: Implications for replication models and risk assessment. Transgenic research 16:587-597. 

3 Azevedo C, Betsuyaku S, Peart J, Takahashi A, Noël L, Sadanandom A, Casais C, Parker J, Shirasu K. 2002. Role of SGT1 in resistance protein accumulation in plant immunity. The EMBO Journal 25:2007-2016. 

4 Baker CA, Breman L, Jones L. 2006. Alternanthera mosaic virus found in Scutellaria, Crossandra, and Portulaca spp. in Florida. Plant Disease 90:833. 

5 Baurès I, Candresse T, Leveau A, Bendahmane A, Sturbois B. 2008. The Rx gene confers resistance to a range of potexviruses in transgenic Nicotiana plants. Molecular Plant-Microbe Interactions 21:1154-1164. 

6 Bayne EH, Rakitina DV, Morozov SY, Baulcombe DC. 2005. Cell‐to‐cell movement of potato potexvirus X is dependent on suppression of RNA silencing. The Plant Journal 44:471-482. 

7 Beck DL, Guilford PJ, Voot DM, Andersen MT, Forster RL. 1991. Triple gene block proteins of white clover mosaic potexvirus are required for transport. Virology 183:695-702. 

8 Bhat S, Folimonova SY, Cole AB, Ballard KD, Lei Z, Watson BS, Sumner LW, Nelson RS. 2013. Influence of host chloroplast proteins on tobacco mosaic virus accumulation and intercellular movement. Plant Physiology 161:134-147. 

9 Brunkard JO, Runkel AM, Zambryski PC. 2015. Chloroplasts extend stromules independently and in response to internal redox signals. Proceedings of the National Academy of Sciences of the United States of America 112:10044-10049. 

10 Büchen-Osmond C, Hiebert E. 1988. Papaya mosaic potexvirus. Plant viruses online. Descriptions and lists from the VIDE database. Accessed in http://sdb.im.ac.cn/vide/descr548.htm on 16 January 1997. 

11 Cakmak I, Römheld V. 1997. Boron deficiency-induced impairments of cellular functions in plants. Plant and Soil 193:71-83. 

12 Candresse T, Marais A, Faure C, Dubrana, MP, Gombert J, Bendahmane A. 2010. Multiple coat protein mutations abolish recognition of pepino mosaic potexvirus (PepMV) by the potato Rx resistance gene in transgenic tomatoes. Molecular Plant-Microbe Interactions 23:376-383.  

13 Caplan JL, Kumar AS, Park E, Padmanabhan MS, Hoban K, Modla S, Czymmek K, Dinesh-Kumar SP. 2015. Chloroplast stromules function during innate immunity. Developmental cell 34:45-57. 

14 Caplan JL, Mamillapalli P, Burch-Smith TM, Czymmek K, Dinesh-Kumar SP. 2008. Chloroplastic protein NRIP1 mediates innate immune receptor recognition of a viral effector. Cell 132:449-462. 

15 Chalcroft J, Matthews REF. 1966. Cytological changes induced by turnip yellow mosaic virus in Chinese cabbage leaves. Virology 28:555-562. 

16 Chellappan P, Vanitharani R, Ogbe F, Fauquet CM. 2005. Effect of temperature on geminivirus-induced RNA silencing in plants. Plant Physiology 138:1828-1841. 

17 Ciuffo M, Turina M. 2004. A potexvirus related to papaya mosaic virus isolated from moss rose (Portulaca grandiflora) in Italy. Plant Pathology 53:515. 

18 Dardick C. 2007. Comparative expression profiling of Nicotiana benthamiana leaves systemically infected with three fruit tree viruses. Molecular Plant-Microbe Interactions 20:1004-1017. 

19 Duarte LML, Toscano AN, Alexandre MAV, Rivas EB, Harakava R. 2008. Identification and control of alternanthera mosaic virus isolated from Torenia sp. (Scrophulariaceae). Revista Brasileira de Horticultura Ornamental 14:59-66. 

20 Erickson JW, Bancroft JB, Horne RW. 1976. The assembly of papaya mosaic virus protein. Virology 72:514-517. 

21 Fridborg I, Grainger J, Page A, Coleman M, Findlay K, Angell S. 2003. TIP, a novel host factor linking callose degradation with the cell-to-cell movement of Potato virus X. Molecular Plant-Microbe Interactions 16:132-140. 

22 Geering ADW, Thomas JE. 1999. Characterisation of a virus from Australia that is closely related to papaya mosaic potexvirus. Archives of Virology 144:577-592. 

23 Gleba Y, Marillonnet S, Klimyuk V. 2004. Engineering viral expression vectors for plants: The ‘full virus’ and the ‘deconstructed virus’ strategies. Current Opinion in Plant Biology 7:182-188. 

24 Goulden MG, Köhm BA, Santa Cruz S, Kavanagh TA, Baulcombe DC. 1993. A feature of the coat protein of potato virus X affects both induced virus resistance in potato and viral fitness. Virology 197:293-302. 

25 Groth G, Strotmann H. 1999. New results about structure, function and regulation of the chloroplast ATP synthase (CF0CF1). Physiologia Plantarum 106:142-148. 

26 Gu Y, Dong X. 2015. Stromules: Signal conduits for plant immunity. Developmental Cell 34:3-4. 

27 Hammond J, Hull R. 1981. Plantain virus X: A new potexvirus from Plantago lanceolata. Journal of General Virology 54:75-90. 

28 Hammond J, Lawson RH. 1988. An improved purification procedure for preparing potyviruses and cytoplasmic inclusions from the same tissue. Journal of Virological Methods 20:203-217. 

29 Hammond J, Reinsel MD, Maroon-Lango CJ. 2006a. Identification and full sequence of an isolate of alternanthera mosaic potexvirus infecting Phlox stolonifera. Archives of Virology 151:477-493. 

30 Hammond J, Reinsel MD, Maroon-Lango CJ. 2006b. Identification of potexvirus isolates from creeping phlox and trailing portulaca as strains of alternanthera mosaic virus, and comparison of the 3-terminal portion of the viral genomes. Acta Horticulturae 722:71-78. 

31 Hammond J, Reinsel MD. 2011. Mixed infections and novel viruses in various species of Phlox. Acta Horticulturae 901:119-126. 

32 Hammond J, Reinsel MD. 2015. Variability in alternanthera mosaic virus isolates from different hosts. Acta Horticulturae 1072:47-53. 

33 Hashimoto M, Komatsu K, Maejima K, Okano Y, Shiraishi T, Ishikawa K, Takinami Y, Yamaji, Y, Namba S. 2012. Identification of three MAPKKKs forming a linear signaling pathway leading to programmed cell death in Nicotiana benthamiana. BMC Plant Biology 12:103. 

34 Henderson DC, Reinsel MD, Fischer KF, Hammond J. 2014. First Detection of ligustrum necrotic ringspot virus, cucumber mosaic virus, and alternanthera mosaic virus in Mazus reptans in the United States. Plant Disease 98:1446. 

35 Ivanov PA, Mukhamedzhanova AA, Smirnov AA, Rodionova NP, Karpova OV, Atabekov JG. 2011. The complete nucleotide sequence of alternanthera mosaic virus infecting Portulaca grandiflora represents a new strain distinct from phlox isolates. Virus Genes 42:268-271. 

36 Iwabuchi N, Yoshida T, Yusa A, Nishida S, Tanno K, Keima T, Nijo T, Yamaji Y, Namba S. 2016. Complete genome sequence of alternanthera mosaic virus, isolated from Achyranthes bidentata in Asia. Genome Announcements 4:e00020-16. 

37 Jang C, Seo EY, Nam J, Bae H, Gim YG, Kim HG, Cho IS, Lee ZW, Bauchan GR, Hammond J, Lim HS. 2013. Insights into alternanthera mosaic virus TGB3 functions: Interactions with Nicotiana benthamiana PsbO correlate with chloroplast vesiculation and veinal necrosis caused by TGB3 over-expression. Frontiers in Plant Science 4:5. 

38 Jovel J, Walker M, Sanfaçon H. 2007. Recovery of Nicotiana benthamiana plants from a necrotic response induced by a nepovirus is associated with RNA silencing but not with reduced virus titer. Journal of Virology 81:12285-12297. 

39 Ju HJ, Samuels TD, Wang YS, Blancaflor E, Payton M, Mitra R, Krishnamurthy K, Nelson RS, Verchot-Lubicz J. 2005. The potato virus X TGBp2 movement protein associates with endoplasmic reticulum-derived vesicles during virus infection. Plant Physiology 138:1877-1895. 

40 Ko NY, Kim HS, Kim JK, Cho S, Seo EY, Kwon HR, Yu YM, Gotoh T, Hammond J, Youn YN, Lim HS. 2015. Developing an alternanthera mosaic virus vector for efficient cloning of whitefly cDNA RNAi to screen gene function. Journal of the Faculty of Agriculture, Kyushu University. 60:139-149. 

41 Koenig R, Lesemann DE, Loss S, Engelmann J, Commandeur U, Deml G, Schiemann J, Aust H, Burgermeister W. 2006. Zygocactus virus X-based expression vectors and formation of rod-shaped virus-like particles in plants by the expressed coat proteins of Beet necrotic yellow vein virus and Soil-borne cereal mosaic virus. Journal of General Virology 87:439-443. 

42 Komatsu K, Hashimoto M, Maejima K, Shiraishi T, Neriya Y, Miura C, Minato N, Okano Y, Sugawara K, Yamaji Y, Namba S. 2011. A necrosis-inducing elicitor domain encoded by both symptomatic and asymptomatic Plantago asiatica mosaic virus isolates, whose expression is modulated by virus replication. Molecular Plant-Microbe Interactions 24:408-420. 

43 Komatsu K, Hashimoto M, Ozeki J, Yamaji Y, Maejima K, Senshu H, Himeno M, Okano Y, Kagiwada S, Namba S. 2010. Viral-induced systemic necrosis in plants involves both programmed cell death and the inhibition of viral multiplication, which are regulated by independent pathways. Molecular Plant-Microbe Interactions 23:283-293. 

44 Krishnamurthy K, Mitra R, Payton ME, Verchot-Lubicz J. 2002. Cell-to-cell movement of the PVX 12K, 8K, or coat proteins may depend on the host, leaf developmental stage, and the PVX 25K protein. Virology 300:269-281. 

45 Laliberté Gagné ME, Lecours K, Gagné S, Leclerc D. 2008. The F13 residue is critical for interaction among the coat protein subunits of papaya mosaic virus. The FEBS Journal 275:1474-1484. 

46 Lee YS, Hsu YH, Lin NS. 2000. Generation of subgenomic RNA directed by a satellite RNA associated with bamboo mosaic potexvirus: Analyses of potexvirus subgenomic RNA promoter. Journal of Virology 74:10341-10348. 

47 Leshchiner AD, Solovyev AG, Morozov SY, Kalinina NO. 2006. A minimal region in the NTPase/helicase domain of the TGBp1 plant virus movement protein is responsible for ATPase activity and cooperative RNA binding. Journal of General Virology 87:3087-3095. 

48 Lim HS, Bragg JN, Ganesan U, Ruzin S, Schichnes D, Lee MY, Vaira AM, Ryu KH, Hammond J, Jackson AO. 2009. Subcellular localization of the barley stripe mosaic virus triple gene block proteins. Journal of Virology 83:9432-9448. 

49 Lim HS, Nam J, Seo EY, Nam M, Vaira AM, Bae H, Jang CY, Lee CH, Kim HG, Roh M, Hammond J. 2014. The coat protein of alternanthera mosaic virus is the elicitor of a temperature-sensitive systemic necrosis in Nicotiana benthamiana, and interacts with a host boron transporter protein. Virology 452:264-278. 

50 Lim HS, Vaira AM, Bae H, Bragg JN, Ruzin SE, Bauchan GR, Dienelt MM, Owens RA, Hammond J. 2010b. Mutation of a chloroplast-targeting signal in alternanthera mosaic virus TGB3 impairs cell-to-cell movement and eliminates long-distance virus movement. Journal of General Virology 91:2102-2115. 

51 Lim HS, Vaira AM, Domier LL, Lee SC, Kim HG, Hammond J. 2010c. Efficiency of VIGS and gene expression in a novel bipartite potexvirus vector delivery system as a function of strength of TGB1 silencing suppression. Virology 402:149-163. 

52 Lim HS, Vaira AM, Reinsel MD, Bae H, Bailey BA, Domier LL, Hammond J. 2010a. Pathogenicity of alternanthera mosaic virus is affected by determinants in RNA-dependent RNA polymerase and by reduced efficacy of silencing suppression in a movement-competent TGB1. Journal of General Virology 91:277-287. 

53 Lin MK, Hu CC, Lin NS, Chang BY, Hsu YH. 2006. Movement of potexviruses requires species-specific interactions among the cognate triple gene block proteins, as revealed by a trans-complementation assay based on the bamboo mosaic virus satellite RNA-mediated expression system. Journal of General Virology 87:1357-1367. 

54 Lockhart BE, Daughtrey ML. 2008. First report of alternanthera mosaic virus infection in angelonia in the United States. Plant Disease 92:1473. 

55 Lough TJ, Netzler NE, Emerson SJ, Sutherland P, Carr F, Beck DL, Lucas WJ, Forster RL. 2000. Cell-to-cell movement of potexviruses: Evidence for a ribonucleoprotein complex involving the coat protein and first triple gene block protein. Molecular Plant-Microbe Interactions 13:962-974. 

56 Lough TJ, Shash K, Xoconostle-Cázares B, Hofstra KR, Beck DL, Balmori E, Forster RL, Lucas WJ. 1998. Molecular dissection of the mechanism by which potexvirus triple gene block proteins mediate cell-to-cell transport of infectious RNA. Molecular Plant-Microbe Interactions 11:801-814. 

57 Lukashina E, Ksenofontov A, Fedorova N, Badun G, Mukhamedzhanova A, Karpova O, Rodionova N, Baratova L, Dobrov E. 2012. Analysis of the role of the coat protein N‐terminal segment in Potato virus X virion stability and functional activity. Molecular Plant Pathology 13:38-45. 

58 Mathioudakis MM, Veiga RS, Canto T, Medina V, Mossialos D, Makris AM, Livieratos I. 2013. Pepino mosaic virus triple gene block protein 1 (TGBp1) interacts with and increases tomato catalase 1 activity to enhance virus accumulation. Molecular Plant Pathology 14:589-601. 

59 Mitra R, Krishnamurthy K, Blancaflor E, Payton M, Nelson RS, Verchot-Lubicz J. 2003. The Potato virus X TGBp2 protein association with the endoplasmic reticulum plays a role in but is not sufficient for viral cell-to-cell movement. Virology 312:35-48. 

60 Morozov SY, Solovyev AG, Kalinina NO, Fedorkin ON, Samuilova OV, Schiemann J, Atabekov JG. 1999. Evidence for two nonoverlapping functional domains in the potato virus X 25K movement protein. Virology 260:55-63. 

61 Mukhamedzhanova AA, Smirnov AA, Arkhipenko MV, Ivanov PA, Chirkov SN, Rodionova NP, Karpova OV, Atabekov JG. 2011. Characterization of alternanthera mosaic virus and its coat protein. The Open Virology Journal 5:136-140. 

62 Nable RO, Bañuelos GS, Paull JG. 1997. Boron toxicity. Plant and Soil 193:181-198. 

63 Nam J, Nam M, Bae H, Lee C, Lee BC, Hammond J, Lim HS. 2013. AltMV TGB1 nucleolar localization requires homologous interaction and correlates with cell wall localization associated with cell-to-cell movement. The Plant Pathology Journal. 29:454-459. 

64 Noa-Carrazana JC, González-de-León D, Ruiz-Castro BS, Piñero D, Silva-Rosales L. 2006. Distribution of papaya ringspot virus and papaya mosaic virus in papaya plants (Carica papaya) in Mexico. Plant Disease 90:1004-1011. 

65 Peart JR, Lu R, Sadanandom A, Malcuit I, Moffett P, Brice DC, Schauser L, Jaggard DAW, Xiao S, Coleman MJ, Dow M, Jones JDG, Shirasu K, Baulcombe DC. 2002. Ubiquitin ligase-associated protein SGT1 is required for host and nonhost disease resistance in plants. Proceedings of the National Academy of Sciences of the United States of America 99:10865-10869. 

66 Prod’homme D, Jakubiec A, Tournier V, Drugeon G, Jupin I. 2003. Targeting of the turnip yellow mosaic virus 66K replication protein to the chloroplast envelope is mediated by the 140K protein. Journal of Virology 77:9124-9135. 

67 Purcifull DE, Hiebert E. 1971. Papaya mosaic virus. CMI/AAB Descriptions of Plant Viruses. No. 56. Accessed in http://www.dpvweb.net/dpv/showdpv.php?dpvno=056 on June 1971. 

68 Putlyaev EV, Smirnov AA, Karpova OV, Atabekov JG. 2015. Double subgenomic promoter control for a target gene superexpression by a plant viral vector. Biochemistry (Moscow) 80:1039-1046. 

69 Qiao Y, Li HF, Wong SM, Fan ZF. 2009. Plastocyanin transit peptide interacts with potato virus X coat protein, while silencing of plastocyanin reduces coat protein accumulation in chloroplasts and symptom severity in host plants. Molecular Plant-Microbe Interactions 22:1523-1534. 

70 Qu F, Ye X, Hou G, Sato S, Clemente TE, Morris TJ. 2005. RDR6 has a broad-spectrum but temperature-dependent antiviral defense role in Nicotiana benthamiana. Journal of Virology 79:15209-15217. 

71 Rubino L, Russo M. 1998. Membrane targeting sequences in tombusvirus infections. Virology 252:431-437. 

72 Samuels TD, Ju HJ, Ye CM, Motes CM, Blancaflor EB, Verchot-Lubicz J. 2007. Subcellular targeting and interactions among the Potato virus X TGB proteins. Virology 367:375-389. 

73 Schepetilnikov MV, Manske U, Solovyev AG, Zamyatnin AA Jr, Schiemann J, Morozov SY. 2005. The hydrophobic segment of Potato virus X TGBp3 is a major determinant of the protein intracellular trafficking. Journal of General Virology 86:2379-2391. 

74 Seo EY, Nam J, Kim HS, Park YH, Hong SM, Lakshman D, Bae H, Hammond J, Lim HS. 2014. Selective interaction between chloroplast β-ATPase and TGB1L88 retards severe symptoms caused by alternanthera mosaic virus infection. The Plant Pathology Journal 30:58-67. 

75 Shivprasad S, Pogue GP, Lewandowski DJ, Hidalgo J, Donson J, Grill LK, Dawson WO. 1999. Heterologous sequences greatly affect foreign gene expression in tobacco mosaic virus-based vectors. Virology 255:312-323. 

76 Siddiqui SA, Sarmiento C, Kiisma M, Koivumäki S, Lemmetty A, Truve E, Lehto K. 2008. Effects of viral silencing suppressors on tobacco ringspot virus infection in two Nicotiana species. Journal of General Virology 89:1502-1508. 

77 Skryabin KG, Morozov SY, Kraev AS, Rozanov MN, Chernov BK, Lukasheva LI, Atabekov JG. 1988. Conserved and variable elements in RNA genomes of potexviruses. FEBS Letters 240:33-40. 

78 Solovyev AG, Makarova SS, Remizowa MV, Lim HS, Hammond J, Owens RA, Kopertekh L, Schiemann J, Morozov SY. 2013. Possible role of the Nt-4/1 protein in macromolecular transport in vascular tissue. Plant Signaling & Behavior 8:e25784. 

79 Sturbois B, Dubrana-Ourabah MP, Gombert J, Lasseur B, Macquet A, Faure C, Bendahmane A, Baurès I, Candresse T. 2012. Identification and characterization of tomato mutants affected in the Rx-mediated resistance to PVX isolates. Molecular Plant-Microbe Interactions 25:341-354. 

80 Takano J, Miwa K, Yuan L, von Wirén N, Fujiwara T. 2005. Endocytosis and degradation of BOR1, a boron transporter of Arabidopsis thaliana, regulated by boron availability. Proceedings of the National Academy of Sciences of the United States of America 102:12276-12281. 

81 Takano J, Noguchi K, Yasumori M, Kobayashi M, Gajdos Z, Miwa K, Hayashi H, Yoneyama T, Fujiwara T. 2002. Arabidopsis boron transporter for xylem loading. Nature 420:337-340. 

82 Tang J, Olson JD, Ochoa-Corona FM, Clover GRG. 2010. Nandina domestica, a new host of apple stem grooving virus and alternanthera mosaic virus. Australasian Plant Disease Notes 5:25-27. 

83 Torrance L, Cowan GH, Gillespie T, Ziegler A, Lacomme C. 2006. Barley stripe mosaic virus-encoded proteins triple-gene block 2 and γb localize to chloroplasts in virus-infected monocot and dicot plants, revealing hitherto-unknown roles in virus replication. Journal of General Virology 87:2403-2411. 

84 Tremblay MH, Majeau N, Gagné MEL, Lecours K, Morin H, Duvignaud JB, Bolduc M, Chouinard N, Paré C, Gagné S. 2006. Effect of mutations K97A and E128A on RNA binding and self assembly of papaya mosaic potexvirus coat protein. The FEBS Journal 273:14-25. 

85 Tyagi A, Hermans J, Steppuhn J, Jansson C, Vater F, Herrmann RG. 1987. Nucleotide sequence of cDNA clones encoding the complete “33 kDa” precursor protein associated with the photosynthetic oxygen-evolving complex from spinach. Molecular and General Genetics MGG 207:288-293. 

86 Ushiyama R, Matthews REF. 1970. The significance of chloroplast abnormalities associated with infection by turnip yellow mosaic virus. Virology 42:293-303. 

87 Vaira AM, Maroon-Lango CJ, Hammond J. 2008. Molecular characterization of Lolium latent virus, proposed type member of a new genus in the family Flexiviridae. Archives of Virology 153:1263-1270. 

88 Verchot-Lubicz J. 2005. A new cell-to-cell transport model for potexviruses. Molecular Plant-Microbe Interactions 18:283-290. 

89 Vitoreli A, Baker CA, Harmon CL. 2011. Alternanthera Mosaic Virus identified in clock vine in Florida. Phytopathology 101:S183. 

90 von Bargen S, Salchert K, Paape M, Piechulla B, Kellmann JW. 2001. Interactions between the tomato spotted wilt virus movement protein and plant proteins showing homologies to myosin, kinesin and DnaJ-like chaperones. Plant Physiology and Biochemistry 39:1083-1093. 

91 Yang S, Wang T, Bohon J, Gagné MÈL, Bolduc M, Leclerc D, Li H. 2012. Crystal structure of the coat protein of the flexible filamentous papaya mosaic virus. Journal of Molecular Biology 422:263-273.