Mechanism Of Rice Stripe Virus Regulating Expression Of Plant Ferredoxin 1

Rice stripe disease is an important virus disease caused by Rice stripe virus(RSV)with severe symptoms and even death of plants,which certainly influence production of rice.Identification the interactions between host and virus benefits the establishment of effective measures for disease control,and provides theoretical basis for breeding cultivars resistant to disease that are of great significant for disease controlling and rice production.FD1 encodes a soluble acceptor of electrons of the chloroplast electron transport chain.Recently,increasing evidences revealed the roles of plant FD1 in plant immunity,and its expression were universally downregulated by various pathogens.However,the regulation mechanism of FD1 expression is still unclear.Here,we focused on exploring the mechanisms of RSV regulating expression of plant FD1.In this study,we found that RSV infection downregulated the expression of FD1 in both N.benthamiana and rice plants.NbFD1 silencing contributed to the accumulation of RSV in N.benthamiana plants,while the FD1-overexpressing transgenic lines of N.benthamiana and rice enhanced plant resistance to RSV infection.We first searched the libraries of small interference RNA and found that a RSV-derived s RNA(vsi R45349)might target NbFD1 transcript for silencing.When vsi R45349 was expressed transiently in N.benthamiana leaves with RSV genomic sequence containing vis R45349 or MIR319 precursor,NbFD1 transcript was decreased to 70% of normal level.Then,the involvement of vsi R45349 in regulating expression of NbFD1 at posttranscriptional level was further confirmed via degradome sequencing.Whereas,vis R45349-mediated downregulation of NbFD1 transcript was not to the much lower levels found in RSV-infected plants.We therefore supposed that there must also be other mechanisms involved in regulating NbFD1 transcript expression during RSV infection.To further explore the possible mechanism of NbFD1 downregulation by RSV,we analyzed the binding sites of potential transcription factors and identified two elements for ABA responsiveness in NbFD1 promoter.Indeed,RSV induced ABA accumulation in infected N.benthamiana plants.Exogenous application of ABA reduced the expression of NbFD1 and reporter genes driven by NbFD1 promoter.After analyzing the transcription factors that participated in ABA signaling,we found ABI5 might be involved in regulating expression of NbFD1.Further studies suggested that NbFD1 expression was upregulated in NbABI5-silenced plants,but downregulated by NbABI5 overexpression.Furthermore,the suppression effect of ABA on NbFD1 expression was attenuated in NbABI5-silenced plants,indicating the involvement of NbABI5 in regulating expression of NbFD1.Yeast One Hybird(Y1H)assay confirmed NbABI5 could bind to NbFD1 promoter directly,but the interaction was attenuated or even abolished when the two ABRE motifs were mutated individually or together.The dual-luciferase assay showed NbABI5 suppressed the transcription from the NbFD1 promoter,but had no effect on that from NbFD1 promoter with two mutated ABRE motifs.The above results demonstrated that NbABI5 was indispensable for ABA-mediated regulation of NbFD1 expression.In rice,ABRE motifs were also identified in Os FD1 promoter and ABA accumulation was two fold greater in RSV-infected plants.We next confirmed the expression of Os FD1 was downregulated in ABA-treated rice plants.In addition,the two Os ABI5 variants in rice that was simulated by ABA treatment and RSV infection,suppressed the transcription of reporter gene from the Os FD1 promoter.The results suggested that FD1 is also regulated by ABA in RSV-infected rice plants.Collectively,our results revealed that in RSV-infected plants,FD1 is downregulated at both transcriptional and post-transcriptional level to facililate RSV infection.