Analysis For Spontaneous Mutagenesis Of Wheat Yellow Mosaic Virus RNA1

Repeated passage of several fungus-transmitted plant viruses can lead to sequence deletion in their hosts. These deleted segments, known as defective RNA (D-RNA) or defective interfering RNA (DI-RNA), affect frequently the biological properties of the helper virus. To further investigate the function of the Wheat yellow mosaic virus (WYMV) gene, the spontaneously deleted region of WYMV genome (designated D-RNA 1) has been identified though serial manual passage of WYMV and the corresponding biological function of the D-RNA 1 were studied.Spontaneous deletion in the RNA1 of WYMV, which is comprised of two RNA components for the whole genome, was shown to occur after the twelfth passage of mechanical inoculation in wheat plants and exist stably in the inoculated plants to the 26th passage in the experiment. Sequence analysis showed that a contiguous segment of 2380 nucleotides was internally deleted from the WYMY RNA1 and flanked by direct repeats of six nucleotides CGTCTC, which supports the "copy choice" model as the possible mechanism of the generation of WYMV D-RNA 1.Associated with WYMV, D-RNA 1 appears to increase manual inoculation efficiency, shorten the latent period and exacerbate symptoms displayed in plants, which stabilized gradually in the late passages after the thirteenth (P13).On sand culture system, the virus-free P. graminis, that was filtrated and isolated by inoculating to WYMV non-host barley, acquired WYMV de novo by mechanical inoculation on wheat. Comparing with the wild type WYMV or WYMV in the early passage, WYMV transmission by P. graminis was affected when the D-RNA 1 was involved, that the infected wheat showed decreased disease incidence, prolonged latent period, reduced virus content and subdued symptoms. This suggests that the occurrence of deletion in WYMV RNA1 doesn't eliminate potential for transmission by P. graminis, but can reduce the transmission efficiency.It is concluded that this D-RNA 1 could be an interfering factor associated with virus replication, which affects not only on WYMV pathogenicity but also on transmission efficiency of P. graminis.