Responses of Some American, European and Japanese Wheat Cultivars to Soil-Borne Wheat Viruses in China

Wheat seeds of 109 cultivars from USA, Europe and Japan were sown in experiments at seven sites in different provinces of China for one or two seasons. Five of the sites were infested with the bymovirus wheat yellow mosaic virus (WYMV) and two jointly with WYMV and the furovirus Chinese wheat mosaic virus (CWMV). Disease symptoms were assessed visually and leaf samples were tested for virus (es) by ELISA. At least 29 cultivars were resistant to WYMV at the sites where only this virus was present but all the cultivars were severely infected at Rongcheng (Shandong Province) where CWMV was mixed with WYMV. There was evidence that the presence of CWMV assisted infection by WYMV and also resulted in more severe symptoms. At the mixed site in Yantai, Shandong Province, symptoms were mild and many cultivars had symptomless infection . Of the two strains of WYMV identified in Japan, the Chinese sites seem to be most similar to the type isolated, WYMV-T. Eleven cultivars seemed to be susceptible to WYMV only at Loutian (Hubei Province),suggesting that the virus at this site would be worth studying further.

A virus-derived siRNA activates plant immunity by interfering with ROS scavenging

Virus-derived small interference RNAs(vsiRNAs)not only suppress virus infection in plants via induction of RNA silencing but also enhance virus infection by regulating host defensive gene expression.However,the underlying mechanisms that control vsiRNA-mediated host immunity or susceptibility remain largely unknown.In this study,we generated several transgenic wheat lines using four artificial microRNA expression vectors carrying vsiRNAs from Wheat yellow mosaic virus(WYMV)RNA1.Laboratory and field tests showed that two transgenic wheat lines expressing amiRNAI were highly resistant to WYMV infection.Further analyses showed that vsiRNAI could modulate the expression of a wheat thioredoxin-like gene(TaAAEDI),which encodes a negative regulator of reactive oxygen species(ROS)production in the chloroplast.The function of TaAAEDI in ROS scavenging could be suppressed by vsiRNAI in a dose-dependent manner.Furthermore,transgenic expression of amiRNAI in wheat resulted in broad-spectrum disease resistance to Chinese wheat mosaic virus,Barley stripe mosaic virus,and Puccinia striiformis f.sp.tritici infection,suggesting that vsiRNAI is involved in wheat immunity via ROS signaling.Collectively,these findings reveal a previously unidentified mechanism underlying the arms race between viruses and plants.