| The interactions between Tomato yellow leaf curl China virus (TYLCCNV) Y10 isolate (Y10) and Tobacco curly shoot virus (TbCSV) Y35 isolate (Y35) with their associated DNAβ molecules (YlOp and Y35P) and molecular variations among YlOp and Y35β populations were investigated in this study.Y35+Y35β, Y35+Y10β, Y10+Y10β and Y10+Y35β were agroinoculated to Nicotiana benthamiana, N. glutinosa plants and N. tabacum Samsun nn, respectively Southern blot analysis showed that both YlOp and Y35P could be trans-replicated by heterogenous geminivirus, but DNAβ molecules associated, with heterogenous helper virus accumulated in plants at a lower level as compared with those associated, with cognate helper virus. Symptoms induced by Y10 or Y35 with their cognate DNAβ were different from those induced by co-infection with heterogenous DNAβ, and high pathogenicity was found in plants inoculated with Y10β and Y35. Southern blot analysis indicated that no direct co-relation existed, between symptom severity and virus and satellite accumulation levels in plants.PCR and Southern blot analyses showed that the heterogenous DNAβ. could not be detected in N. benthamiana and N. glutinosa plants agroinoculated with Y10+Y10β+Y35β or Y35+Y35β+Y10β in later stage of infection. In N. benthamiana plants agroinoculated with Y35+Y10+Y35β or Y35+Y10+Y10β, both viruses and DNAP molecules were detectable in the whole growing period, and the inoculated plants showed milder symptoms as compared with those induced by Y35 or Y10 plus cognate or heterogenous DNAβ. In contrast, symptom antagonism was observed in N. glutinosa inoculated with the same combinations in the early stage of infection, but not observed in later stage of infection, and PCR and Southern blot indicated that Y10 was undetectable at later stage of infection. Presence of viruses and associated DNAβ . molecules could be detected in the whole growing period in N. benthamiana plants agroinoculated with Y35+Y10+Y35β+Y10β, however, Y10 and Y10β only existed in N. glutinosa in the early stage of infection.The population diversity of DNAβ was compared by DNA sequencing of progenies of Y10β and Y35β molecules in N. benthamiana and N. glutinosa plants agroinoculated withY35+Y35β, Y35+Y10p, Y10+Y10β and Y10+Y35β, respectively. Comparisons showed that Y10β and Y35β populations associated with heterogenous helper virus had stronger mutation tendency and higher population diversity than associated with cognate helper virus. Moreover, Y10β and Y35β populations had different levels of mutation frequency in N. benthamiana and N. glutinosa, indicating that hosts may play important role in evolution of DNAβ populations. Most mutations generated in Y10β and Y35β populations were located in A-rich region. No mutation was found in βCl ORF and SCR. Various mutation types including substitution, deletion and insertion occurred in Y10β and Y35β populations, and the same type of mutation in the same nucleotide position was observed in several DNAp clones. The biological significance of the mutation accumulation in disease epidemic is unclear.Pre-inoculation of βCl gene defective mutant of Y10β or Y35β (Y10ΔC1β and Y35AC1β) with cognate virus could mediated cross-protection to challenge-infection of cognate or heterogenous helper viruses and associated DNAp. All N. benthamiana and N. glutinosa plants pre-inoculated with Y10+Y10ΔC1β or Y35+Y35AC1β exhibited mild symptoms after challenge inoculation with Y10+Y10P or Y35+Y35β, but better protection effects were found for cognate helper viruse and associated DNAp, and protection effects in N. benthamiana were better than those in N. glutinosa. The above results will have important role for control of TYLCCNV and other begomo viruses.Y128 isolate was obtained from tobacco in Baoshan, Yunnan province. The PCR amplification proved that Y128 is an isolate of TbCSV. Satellite DNA molecule (Y128β) was found to be associated with Y128 and the complete nucleotide sequence of Y128β was determined to be 1350 nucleotides. Y128p has 85...
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