A mutation in the cytokinin receptor CRE1 enhances susceptibility to tobacco mosaic virus in Nicotiana tabacum

Cytokinin (CTK)-mediated pathways play essential roles in plant stress responses. How CTK receptors affect plant resistance to viral pathogens remains unclear. Tobacco mosaic virus [recombinant TMV encoding green fluorescent protein (TMV-GFP)] was used to investigate the role of Nicotiana tabacum CRE1 (CTK receptor 1) in modulating virus susceptibility in N. tabacum. CRE1 deficiency enhanced the susceptibility of N. tabacum to TMV-GFP. The cre1 RNAi mutants showed extensive green florescence and higher transcript levels of the TMV coat protein gene than the wild type (WT) plants. CRE1 deficiency affected the antioxidant response to TMV-GFP, and the RNAi mutants had depressed antioxidant enzyme activities compared to the WT plants under virus infection. In addition, endogenous salicylic acid (SA) accumulation and the expression levels of SA pathway-related defence genes induced by TMV-GFP were significantly repressed in the RNAi mutants compared with the WT plants. Furthermore, the presence of exogenous CTK could only partially reduce the susceptibility of tobacco to TMV caused by CRE1 deficiency. Taken together, these results suggest that CRE1 plays a positive role in the tobacco defence response to the virus and is required for the induction and development of complete defence responses.