The Role Of ABA In Tomato Resistance To Grey Leaf Spot Disease

Tomato?Solanum lycopersicum?is not only an important vegetable,but also a classic model for study on plant immunity.There are at least 200 diseases infecting tomato that have caused severe damage to tomato production.Recently,grey leaf spot disease has become more and more serious for crop production.It is caused by fungal pathogen Stemphylium spp.Tomato is one of the most important crops being damaged by grey leaf spot disease.Tomato grey leaf spot disease can cause up to 80%of yield loss.Currently,grey leaf spot disease has occurred in many fields in China.Due to the lack of study,the pathogenesis of gray leaf spot and the mechanism of host resistance are still unclear.In addition,there are no reliable resistant germplasm of tomato or effective disease control.Thus,under this circumstance a disease-resistant germplasm and the mechanism of plant defense against gray leaf spot are not only urgent for tomato production but also an important scientific question.We have isolated and purified the pathogen?Stemphylium lycopersici?of tomato gray leaf spot from diseased tomato leaves and established an effective infection system for study on plant resistance to grey leaf spots.In this study we used tomato as a model,aimed to screen new disease-resistant germplasm and reveal the molecular basis of plant defense against gray leaf spot.First,more than 1000 tomato germplasm lines were screened for disease resistance.It showed that tomato genetic background determined resistance to gray leaf spot.We found that sitiens?sit?,an ABA synthesis mutant,was highly immune to gray leaf spot.Second,we further studied the mechanism of resistance of sit mutants to grey leaf spot.It suggests that H₂O₂ was synthesized earlier in the infected sites of sit leaves than the wild type tomato.When ABA was applied to sit the production of H₂O₂ in sit mutant was similar to that of wild type.Also,the exogenous ABA rescue the susceptibility of sit to wild type level.The results suggest that deficiency in ABA synthesis leads to a disease-resistant phenotype in tomato plants.Finally,we identified homologous genes involving in ABA biosynthesis in tomato based on homolog search to Arabidopsis genome.By real-time quantitative PCR reaction,we detected the expression of genes related to ABA synthesis in tomato after pathogen infection.It was found that the ABA synthase gene was induced by infect of the gray leaf spot pathogen.These results indicate that ABA controls plant resistance to gray leaf spot by regulating H₂O₂.Based on these results,in future we will modify the ABA synthesis in tomato and increase tomato resistance to gray leaf spot.In summary,the level of ABA play an important role in maintaining resistance of tomato to gray leaf spot.Low level of ABA led to early H₂O₂ accumulation at the infected site and thus increase tomato resistance to gray leaf spot.This study indicates that artificially modification of ABA content in plants could be an effective approach to enhance the plant's resistance to gray leaf spot,which also provides important information for creating disease-resistant germplasm and molecular basis of plant immunity.