RESUMEN
The outcome of certain plant-virus interaction is symptom recovery, which is accompanied with the emergence of asymptomatic tissues in which the virus accumulation decreased dramatically. This phenomenon shows the potential to reveal critical molecular factors for controlling viral disease. MicroRNAs act as master regulators in plant growth, development, and immunity. However, the mechanism by which miRNA participates in regulating symptom recovery remains largely unknown. Here, we reported that miR172 was scavenged in the recovered tissue of tobacco mosaic virus (TMV)-infected Nicotiana tabacum plants. Overexpression of miR172 promoted TMV infection, whereas silencing of miR172 inhibited TMV infection. Then, TARGET OF EAT3 (TOE3), an APETALA2 transcription factor, was identified as a downstream target of miR172. Overexpression of NtTOE3 significantly improved plant resistance to TMV infection, while knockout of NtTOE3 facilitated virus infection. Furthermore, transcriptome analysis indicated that TOE3 promoted the expression of defense-related genes, such as KL1 and MLP43. Overexpression of these genes conferred resistance of plant against TMV infection. Importantly, results of dual-luciferase assay, chromatin immunoprecipitation-quantitative PCR, and electrophoretic mobility shift assay proved that TOE3 activated the transcription of KL1 and MLP43 by binding their promoters. Moreover, overexpression of rTOE3 (the miR172-resistant form of TOE3) significantly reduced TMV accumulation compared to the overexpression of TOE3 (the normal form of TOE3) in miR172 overexpressing Nicotiana benthamiana plants. Taken together, our study reveals the pivotal role of miR172/TOE3 module in regulating plant immunity and in the establishment of recovery in virus-infected tobacco plants, elucidating a regulatory mechanism integrating plant growth, development, and immune response.
RESUMEN
MiRNAs play an important role in regulating plant growth and immune response. Mosaic diseases are recognized as the most important plant diseases in the world, and mosaic symptoms are recovery tissues formed by plants against virus infection. However, the mechanism of the formation of mosaic symptoms remains elusive. In this study, two typical mosaic systems consisting of Nicotiana tabacum-cucumber mosaic virus (CMV) and N. tabacum-tobacco mosaic virus (TMV) were used to investigate the relevance of miRNAs to the appearance of mosaic symptoms. The results of miRNA-seq showed that there were significant differences in miRNA abundance between dark green tissues and chlorotic tissues in mosaic leaves caused by the infection of CMV or TMV. Compared with healthy tissues, miRNA expression was significantly increased in chlorotic tissues, but slightly increased in dark green tissues. Three miRNAs, namely miR1919, miR390a, and miR6157, were identified to be strongly up-regulated in chlorotic tissues of both mosaic systems. Results of overexpressing or silencing of the three miRNAs proved that they were related to chlorophyll synthesis, auxin response, and small GTPase-mediated immunity pathway, which were corresponding to the phenotype, physiological parameters and susceptibility of the chlorotic tissues in mosaic leaves. Besides, the newly identified novel-miRNA48, novel-miRNA96 and novel-miRNA103 may also be involved in this formation of mosaic symptoms. Taken together, our results demonstrated that miR1919, miR390a and miR6157 are involved in the formation of mosaic symptoms and plant antiviral responses, providing new insight into the role of miRNAs in the formation of recovery tissue and plant immunity.