Morphological And Molecular Characterization Of A Tobacco Powdery Mildew Used As A Tool To Investigate Post-invasion Resistance In Arabidopsis

Powdery mildew fungi are widespread plant pathogens that cause devastating damage on a wide range of plants, and it is an economically important plant disease with a persistent impact on wheat, barley and rye production.It is with the popular recent that identification of fungal species pathogenic on Arabidopsis to complete the model of plant-pathogen interaction. Arabidopsis-powdery mildew interaction has been successfully used as the prototype for study and understand of biotrophic fungi-plant interactions in general. To elucidate plant-powdery mildew interactions, a tobacco powdery mildew isolate designated Golovinomyces cichoracearum SICAU1.1. Molecular phylogenetic analysis of the fungus to a subgroup of Golovinomyces cichoracearumThe isolate has two different nucleotide sequence site compared with Gc UCSC1, through to comfirm which group it is, we do analysis their ITS sequence. The isolate of tobacco powdery mildew is classified in a subgroup that contains G. cichoracearum, and named the isolate of Gc SICAU1.2. Gc SICAU1 can ivasive the tobacco and ArabidopsisSome pathogens are highly specialized and other are able to colonize a few hosts. Subsequently, we dissect the host range of Gc SICAU1 and inoculate the purified isolate in Arabidopsis, Benlhamiana, cucumber, tomato, pea, pumpkin and lettuce leaves. We found that just in tobacco the conidia can well growing, and had some limit in Arabidopsis and Benthamiana. Gc SICAU1 has weak virulence and is partically stopped by post-invasion resistance of Arabidopsis thalinan.3. Arabidposis shows post-invasion resistance to Gc SICAU1Before the non-adapted pathogen successes to penetrate the cell and develops the complete haustorial, the plant shows penetration resistance which often related PAMP-triggered immunity (PTI). However, Gc SICAU1 is not weakened by the PTI or pen1-1 triggered resistance mechanism, as no significant difference in the fls2,efr-1 and pen1-1 mutant comparing with wild type (Col-0). The post-invasion resistance is primary assumed that plant immunity referring to systemic signals emanating from infection sites, which include callose deposition, production of reaction oxygen species (ROS). In Arabidopsis, two signaling pathways leading to the activation of defense gens in response to pathogen attack. The pathway is dependent upon perception of the plant hormones jasmonic acid and ethylene. Ethylene (ET) defence pathway related mutant ein2-1 does not appear to limit Gc SICAU1 growth and has a litte promote to susceptible. Thus, ethylene pathway may not appear to contribute resistance to Gc SICAU1 during the compatible interaction.4.Post-invasion resistance to Gc SICAU1 is SA-dependent in Arabidopsis.The more important pathway induces a suite of defense genes via a salicylic acid-dependent mechanism. Hormone deficient as pad4-1, nprl-1, pad4-1/sid2-1, syp121/122/pad4/sid2 mutants and NahG transgenic line all show increased susceptibility to Gc SICAU1, indicating that flux through the sacylic acid signaling pathway limits Gc SICAU1 growth. Host defense limit pathogen growth, mutant edsl-2 shows fully susceptibility to Gc SICAU1 and eds5-1 result in increase disease symptoms. In this process, we found that double mutant pad4-1/sid2-1 is super susceptible to Gc SICAU1 which shows significant different to wild type and single mutant pad4-1. Interestingly, inoculating with Gc SICAU1, the infection leaves turn yellow and the cell commence to death in wild type, however, the double mutant pad4-1/sid2-1 infected leaves keep green.5.PAD4 and SID2 are the key factors for Gc SICAU1 to invasive plantThus, this partial breakdown of post-invasion resistance seemed to be associated with genes pad4 and sid2, we even could infer that either PAD4 and SID2 can compensate for each other function in post-invasion resistance.Cumulative mutations in SA signaling pathway can transform a poor-adapted powdery mildew fungus into a full-fledged pathogen, suggesting that mutations in hormones signaling pathways. For the most important, the marvellous phenotype in double mutant pad4-1/sid2-1 makes Gc SICAU1 can be a useful tool to detect post-invasion resistance which probably represents how is the poorly adapted pathogen transform to the super adapted pathogen. We want to do further study to investigate the molecular mechanism.Taken together, all these findings of the powdery mildew on tobacco leaves confirm that the Gc SICAU1 is a weak virulence pathogen on Arabidopsis, providing the unique use of it in the post-invasion resistance in the crop-pathogen research.