MOLECULAR CHARACTERIZATION AND PHYLOGENETIC STUDIES OF COMPONENT SIX OF BANANA BUNCHY TOP BABUVIRUS (BBTV DNA-6)‏

Abstract

Banana and plantations (Musa sp.) are the most fourth most important global food crop after rice, wheat and maize (Piertersen and Thomas, 2001). Banana plantations are subjected to various natural climates but diseases; in particular, viral diseases constitute a major setback to this crop worldwide. Among viral infections, Banana Bunchy Top Virus (BBTV) is the most serious virus affecting banana in Egypt as well as the world (Dale, 1987; Othman et al., 1996; Harish et al., 2008) and is responsible for the massive reduction in banana crop yield. The symptoms of BBTD are yellowing, dark green streaks on midrib, petioles, extending down into pseudostem, dark green dots and dashes along the minor leaf veins, stunted growth with bunchy top appearance (Magee, 1940; Vetten et al., 2005). BBTV belong to genus Babuvirus and family Nanoviridae with isometric particles of 18-20 nm in diameter. It is naturally transmitted, in persistence manner, by banana aphid Pentalonia nigronervosa (Hu et al., 1996). BBTV is identified as a phloem-limited virus used to occur in low concentration in banana-infected plants (Harding et al., 1991 and 2000). The virus has a single coat protein with molecular weight (Mr.) of about 20-21kDa (Dietzgen and Thomas, 1991; Harding et al., 1991; Sadik et al., 1999). The viron consists of at least six components of circular ssDNA each component of the BBTV genome contains one large (monocistronic) transcriptional active open reading frame (ORF) except BBTV DNA 1 contains two ORFs one master replication protein (Rep) ORF (Hafner et al., 1997) and a small ORF internal to major ORF (Beetham et al., 1997). Additionally, two conserved region: stem-loop common region (CR-SL) and major common region (CR-M), potential TATA box at 3 ' of the stem-loop and polyadenylation signal (Burns et al., 1995; Beetham et al., 1997 and 1999). The nucleotide sequence of the component six of Australian isolate BBTV has 1089 nt. (Burns et al., 1995). The encoded protein of BBTV DNA-6 is a nuclear shuttle protein and is preferentially targeted to the nucleus when expressed alone however in the presence of the movement protein it targeted to the cell periphery (Wanitchakorn et al., 2000a). The aim of this study is to amplify, clone and sequence the full length of BBTV DNA-6 and compare it with other published sequences of the corresponding sequence.