Tm-2~2 Confers Different Resistance Responses against Tobacco mosaic virus Dependent on Its Expression Level

摘要

The innate immunity system of plants can be summarized into two clades. The former clade, where resistant processes are mediated by pattern recognition receptors, is termed pathogen-associated molecular patterns-triggered immunity and the latter is termed effector-triggered immunity (ETI), where R proteins play crucial roles. In most typical ETI, the recognition of pathogen-encoded avirulence effectors by R proteins or its genes activates defense response associated with hypersensitive response (HR)(Jones and Dangl, 2006), which is characterized by the rapid death of plant cells at the pathogen infection sites (Thomma et al., 2011). Another type of ETI conferred by R genes is termed extreme resistance (ER), which manifests no visible necrotic lesions at either local infection sites or systemic tissues. ER may result from undetectable accumulation of pathogen or rapid activation of resistance response at the single-cell level (Yamaji et al., 2012). However, it has remained unknown what causes an Rgene to confer ER or typical resistance associated with HR.A well-known case of ER is Tm-2~2-mediated resistance to Tomato mosaic virus (ToMV) or Tobacco mosaic virus (TMV). Both ToMV and TMV belong to tobamoviruses, which are linear single-strand sense RNA viruses, and cause a great deal of crop damage in Solanaceae and other economical crops. Tm-22 is originally isolated from tomato and confers ER against ToMV and TMV by recognizing viral movement proteins (MP). 7777-2~2-mediated resistance has been successfully used for decades to protect tomato plants against ToMV infection (Lanfermeijer et al., 2003). Very recently, we found that RuBisCO small subunit was involved in 7m-2~2-mediated ER (Zhao et al., 2013). However, it remains unknown why Tm-2~2 confers ER against tobamoviruses.