Positive role of phytochromes in Nicotiana tabacum against Cucumber mosaic virus via a salicylic acid-dependent pathway

Abstract

Previous literature indicates that both light and photoreceptors may play key roles in host susceptibility to viruses. Studies have already suggested that phytochrome B is essential for the defence strategies of Nicotiana tabacum against Cucumber mosaic virus (CMV). Here, further investigations are made into the roles of phytochromes in N. tabacum against CMV. The recombinant vector pRNAi-LIC-PHYA/PHYB was used to produce tobacco phyA, phyB and phyAphyB mutants via the Agrobacterium-mediated transformation method. The results suggest that both phyA and phyB deficiency increase the susceptibility of N. tabacum to CMV infection. Mutant plants showed more obvious CMV-induced symptoms and higher transcriptional levels of the CMV coat protein gene than wild type plants, and the effect was clearly synergistic in the phyAphyB double mutant. Furthermore, the data show that mutations in phyA/phyB up-regulate the sensitivity of N. tabacum to CMV by repressing the salicylic acid (SA)-mediated defence pathway in tobacco plants. Additionally, the results indicate that phytochrome signalling strongly modulates the response of N. tabacum to endogenous SA but not to endogenous jasmonic acid. Taken together, these results reinforce the idea that intact phytochrome signalling plays a positive role in the ability of N. tabacum to resist CMV and is required for the induction and development of SA-mediated defence responses in CMV-inoculated N. tabacum.