Molecular Mechanism Of Interaction Between Sclerotinia Sclerotiorum And Arabidopsis Thaliana

Sclerotinia sclerotiorum (Lib.) de Bary is a worldwide plant pathogen causing destructive Sclerotinia stem rot disease in many oil crops, vegetables, etc. Sclerotinia stem rot disease is particularly important in production of soybean and greenhouse vegetables in our country, and can cause destructive yield loss when the disease is severe. There is no evidence to reveal that pathogen and host interaction follows the typical gene-for-gene relationship. This has brought great difficulty to study the molecular mechanisms underlining the pathogenesis, so the mechanism of S. sclerotiorum-plant interaction still remains unclear. To study molecular plant-microbe interaction, our laboratory started up a long term functional genomics project by generating a large scale activation-tagging library of Arabidopsis thaliana. Interestingly, when we grew Arabidopsis, a Sclerotinia stem rot like disease happened severely. Since there is no any record on Arabidopsis Sclerotinia stem rot, we first identified the pathogen and then studied the molecular mechanism of Arabidopsis- Sclerotinia interaction.We first observed the infection process of Arabidopsis stem rot disease. The mycelium was not detected at 4h after inoculation, but at 8h after inoculation, mycelium was found surrounding the host cell, the end of mycelium swelled and generated many ramuses, then formed infestation stilt, but there were no lesions observed. The inoculated detached leaves showed water-soaked lesions at 12hpi and rapidly expanded to the petiole. Naturally infected plants developed symptoms from water-soaked stem lesions into necrotic tissues that subsequently develop patches of fluffy white mycelium, often with sclerotia and became wilt, typical symptom caused by Sclerotinia sclerotiorum. The fungal hyphae are hyaline, septate, branched and multinucleate. Sclerotia germinated to produce apothecia when buried in a petri dish with wet sandy overwinter. Apothecia produced ascospores, with singular cell but with two nuclei in each ascospore. Taking all these characters together, we concluded that Arabidopsis Sclerotinia stem rot was caused by Sclerotinia sclerotiorum. To our knowledge, this is the first report of Sclerotinia stem rot in ArabidopsisInterestingly, both Arabidopsis and S. sclerotiorum were whole genome sequenced, which set up a good model system to study none gene-for-gene relationship of plant-microbe interaction. To reach this goal, we first investigated the pathogenesis-related genes (PR) expression profile during the infection. Arabidopsis thaliana wild type Col-4 was inoculated with the fungal pathogen and sampled at 0, 4, 8, 12, 16, 20, 24, 48hrs post-inoculation for total RNA extraction and observation of the disease development. The gene PDF 1.2 were used as probes for Northern blot analysis and PR1 gene were used for RT-PCR. The results showed that expression of PDF 1.2 gene were induced at 12 hrs post-inoculation and increased gradually from 12 hours post-inoculation to 48hrs post-inoculation, while the expression of PR1 gene did not change. Combining the results of molecular analysis and infection progress observation, we concluded that expression of PDF 1.2 is related with disease development of S.sclerotiorum, which may suggest that JA/ET signal pathway is involved in the defense system.