SH Tan1,2, M Nishiguchi3, M Murata2 and F Motoyoshi2

1Department of Biotechnology, Faculty of Food Science and Biotechnology, University Putra Malaysia. Serdang 43400, Malaysia; 2Research Institute for Bioresources, Okayama University, Kurashiki 710, Japan; 3National Institute of Agrobiological Resources, Tsukuba, Ibaraki 305, Japan

Background and objectives
Tobamovirus species causing diseases in cucurbitaceous crops have been first recorded in Japan in late 1960s. A virus strain isolated from cucumber in Tokushima Prefecture was first described as cucumber green mottle mosaic virus (CGMMV)[1,2] but later classified as C-strain of kyuri green mottle mosaic virus (KGMMVC)[3]. Another KGMMV strain (KGMMV-Y) similar but not identical to KGMMV-C was collected from cucumber in Yodo, Matsuyama-city [4]. A strain of CGMMV was first recorded in watermelon in Chiba Prefecture and called 'watermelon strain' of CGMMV (CGMMV-W)[2]. CGMMV-SH, another strain of CGMMV that was identified from greenhouse-grown muskmelon in Shizuoka Prefecture, is the only strain whose genomic sequence has been completely determined [5]. The present study is intended to clarify the intra and interspecific molecular variations in KGMMV and CGMMV and the common features of the two virus species, which are distinct from other tobamoviruses.

Results and conclusions
Using cDNAs of the viral genomic RNAS, the complete nucleootide sequences of KGMNIV-Y and CGMMV-W were determined and part of the KGMMV-C genome was also sequenced which included ORFs encoding the coat and the 29 ;kDa putative movement proteins. The genome of KGMMV-Y is 6519 nucleolides long and its organization is almost parallel to that of CGMMV-SH which is 6423 nucleolides long. The sequences of KGMMV-Y, KGMMV-C, CGMMV-W and CGMMV-SH were compared intra- and interspecifically. One amino acid substitution was found in the 29 ;protein between KGMMV-Y and KGMMV-C, while 20 amino acid substitutions were found in the coat protein. In a comparison between CGMMV-W and CGMMV-SH, no amino acid substitutions was found in the coat protein. A total of nine amino acid substitutions were found, six of which ocurred in the 129/186 ;kDa protein region and three in the 29 ;kDa protein. In interspecific comparison between KGMMV-Y and CGMMV-SH, the identities of amino acid sequence are 58% in the 129/186 ;kDa protein, 60% in the 29 ;kDa protein and 46% in the coat protein. Two regions, one in the 129 ;kDa protein (and also in the 186 ;kDa protein) and the other in the 29 ;kDa protein, were found to be remarkably conserved between KGMMV-Y and CGMMV-SH but much less conserved in six other tobamoviruses. In three phylogenic trees constructed based on identities in the deduced amino acid sequences of the 186 ;kDa protein, the 29 ;kDa protein and the coat protein, KGMMV and CGMMV formed one cluster which did not include any other tobamoviruses, suggesting that KGMMV is related most to CGMMV among the tobamoviruses examined.

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