Abstract:

Objective: In this paper, the expression dynamics of key genes in salicylic acid and jasmonic acid/ethylene signaling pathway in rosa were monitored in order to clarify the roles and regulatory mechanisms of salicylic acid and jasmonic acid/ethylene signaling pathways in rose in response to Diplocarpon rosae. Method: The detached leaves of cultivar Rosa 'MEIbil' compatible with D. rosae(cfcc87205) was used as the test materials, and five treatments, including inoculation with D. rosae (CK+IN), 2 mmol·L^-1 SA-induced for 2 h and non-inoculation(SA+NO), 2 mmol·L^-1 SA-induced for 2 h and inoculation(SA+IN), 0.2 mmol·L^-1MeJA-induced for 2 h and non-inoculation(JA+NO), 0.2 mmol·L^-1MeJA-induced for 2 h and inoculation(JA+IN), and blank control(CK), were set. The leaves were sampled from 16-144 h post-treatments and the expressions of ICS, NPR1 and PR1 in salicylic acid signaling pathway and the expressions of AOS, JAR, COI1 and MYC2 related with jasmonic acid signaling pathway were detected through RT-qPCR analysis technique. The difference of expression amount of each gene at the same time point over different treatments and the expression dynamics of each gene under the same treatments were analyzed comprehensively. Result: In CK+IN treatment, ICS was down-regulated (P ≤ 0.05), NPR1 was up-regulated at 16 h and down-regulated continuously from 48-144 h post-inoculated(P ≤ 0.05), PR1 and JAR1 were down-regulated at 48 and 16 h post-inoculated (P ≤ 0.05), respectively, but there were no significant differences with CK in other time points. AOS was up-regulated at 16 h, down-regulated at 72 h, and there was no significant difference with CK treatment at 24, 48 and 144 h post-inoculated(P ≤ 0.05). COI1 was up-regulated from 24 to 72 h post-inoculated (P ≤ 0.05). MYC2 was up-regulated at 16 h, and down-regulated at 24, 72 and 144 h post-inoculated (P ≤ 0.05), however there was no significant difference with CK treatment at 48 h. In SA+IN treatment, ICS, NPR1, PR1 and AOS were up-regulated (P ≤ 0.05), there was no significant difference in JAR1 expression between SA+IN and CK+IN treatment(P ≤ 0.05), COI1 was down-regulated from 24 to 144 h post-inoculated(P ≤ 0.05), MYC2 was up-regulated at all time points except at 16 and 48 h post-inoculated(P ≤ 0.05) at which there had no significant difference with CK+IN treatment. In JA+IN treatment, the expression of ICS was up-regulated at all time points except at 16 h post-inoculated(P ≤ 0.05) at which the expression was down-regulated. The expression of PR1 had no significant difference from that in CK+IN treatment before 48 h, and then up-regulated (P ≤ 0.05), while the expressions of AOS and MYC2 were up-regulated especially before 48 h post-inoculated(P ≤ 0.05), and JAR1 had no significant difference from that in CK+IN treatment except up-regulated at 24 h. In addition, the expression variation trends of NPR1 and COI1 were consistent with those in SA+IN treatment. The results showed that D. rosae inhibited the synthesis of salicylic acid and the active jasmonic acid. SA+IN treatment was able to increase the expressions of genes in salicylic acid signaling pathway and promote the synthesis of jasmonic acid, but had little effect on the synthesis of active jasmonic acid. Meanwhile SA+IN treatment weakened the induction effect of D. rosae on MYC2 before 48 h post-inoculation, while the treatment increased the expressions of both ICS and PR1 as well as the expression of MYC2 after 48 h post-inoculated. JA+IN treatment not only promoted synthesis of active jasmonic acid and the expression PR1 but also increased the expression of MYC2. In addition, this study also found that in the SA+NO and JA+NO treatments, the expression levels of 7 genes changed to different degrees compared with that in CK treatments, but the change trends were inconsistent with the corresponding SA+IN and JA+IN treatments, indicating that D. rosae affected the induced expression of genes of the host by exogenous salicylic acid and jasmonic acid on the corresponding signaling pathway. Conclusion: In conclusions, D. rosae has a strong inhibitory effect on the salicylic acid and jasmonic acid/ethylene signaling pathways of rose, and mainly inhibits salicylic acid signaling pathway before 48 h post-inoculation, and mainly inhibits the jasmonic acid/ethylene signaling pathway after 48 h post-inoculated. The pathogen, D. rosae, may realize dual inhibition of salicylic acid and jasmonic acid/ethylene signaling pathways of rose by enhancing the expression of MYC2 in roses.

Key words: black-spot disease, compatibility interaction, salicylic acid, jasmonic acid, MYC2 transcription factor