Study On Molecular Variability Of CP And SP Genes Of Rice Stripe Virus And Varieties Resistance In Northern China

Rice stripe virus (RSV) is a typical member of Tenuivirus. It causes rice stripe disease, one of the most serious diseases in rice. In recent years, this disease has become increasingly severe and brought great yield losses in northern China due to climatic changes, adjustment of cultivation structure and loss of varieties resistance. In this paper, resistance to rice stripe virus in 25 local rice varieties was screened by artificial inoculation. In addition, the frozen leaf tissue carrying virus was successfully transmitted to rice by small brown planthoppers. The method provides a convenience for further studying the relationship between molecular variability and pathogenity of RSV. The molecular variability of CP and SP gene of RSV was studied by using the isolates obtained from northern China.Twenty-five rice varieties, which were mostly cultivated in Henan Province, Anhui Province, Shandong Province, were screened for resistance to RSV by artificial inoculation in seedlings at greenhouse. The results indicated that the varieties 'Yangjing9538 'Shuijing3 'Kendao95-4', 'Nuhe0218 '04G886' and '04G1020' are highly resistant varieties while '04G824', 'Luhe301 'Zhendao88' and 'V6' are moderately resistant. The others are susceptible and accouted for 60% of the whole variety.The different symptoms displaying on rice by inoculating the same isolate (RSV-JS) to 25 rice entries showed that the leaf-folded and leaf-unfolded symptoms were closely related to the resistance of rice varieties.Thirty-four coat protein genes of RSV isolates collected from northern China were sequenced. The result indicated that the CP genes of all isolates were composed of 969 nts and coded 322 amino acids. The identities of nucleotides and amino acides sequences of CP gene in these isolates and 4 isolates from Yunnan province and T isolate from Japan reached 93.9% -100% and 96.8%-100%, respectively. When compared with sequences of all isolates, we found that the isolates of RSV could be divided into two groups. Isolates from Yunnan Province constituted one group and others shared the second group. The identities of nucleotide sequences of CP genes of isolates obtained from northern China reached 96.8%-100%. According to phylogenetic tree which was constructed based on the sequences of CP genes of isolates from northern China, the grouping was not evident and 22 animo acid sequcences of isolates are identical. All these 22 isolates accounted for most of isolates collected from nine regions of six provinces in northern China. The results indicated that this RSV group was a dominant population in northern China.In this study, we sequenced SP genes of 12 RSV isolates. The results exhibited that the SP gene of all 12 isolates comprised 537nts and coded 178 amino acids, which was same to those ofthe isolate YYLl from Yunnan Provience and T isolates from Japan which had reported. The identities of nucleotide sequences of SP genes of 12 isolates and YYLl and T isolates are from 73.2% to 100%. These 14 isolates can be dividedd into two groups clearly according to the identities of SP gene. The molecular variability of SP gene is very interesting. The mutation sites focus mainly on the third code.We compared the variabilty of CP and SP genes from 14 isolates and found that polymorphism of SP genes was better than that of CP genes. This results showed that CP genes was more conserved than SP genes.