Study On The Mechanism Of Botrytis Cinerea's Participation In Disease Ethylene Synthesis

Pathogenic fungi cause enormous losses to postharvest fruits and vegetables,and the disease ethylene(ET)burst is associated with disease development.The outbreak of disease ET can accelerate the softening and senescence of fruits and vegetables.In addition,exogenous ET also promotes the growth and pathogenic process of fungi,which shown that the disease ET may play a significant effect on both sides of the interaction.Studies have shown that host plants and pathogenic fungi can synthesize ET through the Yang cycle or the KMBA pathway,respectively.But the source and mechanism of disease ET release are still unclear;besides,the enzymes of KMBA pathway are still unknown.In this thesis,we studied the source and synthesis process of disease ET in “plant-Botrytis cinerea” pathosystem,and investigated the molecular and chemical mechanism of the KMBA pathway in B.cinerea.The specific conclusions are as follows:1.In the investigation of the source of the disease ET,we finally determined that disease ET produced by both host plants and pathogenic fungi.But the fungi-induced botanic KMBA decomposition is the main way for outbreak of disease ET.Besides fungi can also slowly assimilate plant-derived L-Met to release ET.2.The chemical mechanism of fungi induced decomposition of KMBA was further investigated using analysis of the effects of different wave-length lights and oxygen radicals on ET synthesis in fungi and their pathosystems.We determined that blue light is the most effective light quality to promote KMBA decomposition.In addition,it has been proved that oxygen radicals from fungal secretions are the final substances to promote the decomposition of KMBA.3.The ET emission was detected in real-time in pathosystem,physical damage system and healthy fruits,respectively.We found that the light-induced ET production is specific in fungi and their pathosystems.Besides,the fungal disease can be accurately predicted in the early stage by detecting light-induced ET burst.Based on this principle,we presented a non-destructive device for fungal diseases detection.4.The deamination of L-Met is the rate-limiting step in KMBA pathway.Through homologous comparison with vas1 in Arabidopsis thaliana and bcaro8 in Saccharomyces cerevisiae and q PCR,we screened and named five homologous genes,bcvas1,bcvas2,bcaro1,bcaro2 and bcaro3.Using the single gene knockeout strategy,we determined that the bcaro2 gene encoded one of the main speed limited enzyme in KMBA pathway of B.cinerea and the bcvas2 mainly promoted ET release in dark condition.In addition,bcvas1,bcaro1 and bcaro3 negatively regulate the ET synthesis.In summary,the main source,release law and regulatory mechanism of disease ET burst in "plant-fungi" pathosystem were studied and the important role of fungi in disease ET release was firstly reported in this thesis.Finally we proposed the model of disease ET production in “plant-Botrytis” pathosystem.We also screened out the main transaminase of KMBA pathway in B.cinerea,and further clarified the chemical mechanism of KMBA decomposition.In terms of theoretical research,this thesis describes the causes and regulatory mechanisms of the outbreak of disease ET,which provides a theoretical basis for further exploration of the regulatory role of fungal disease ET at different stages of infection.In the aspect of postharvest biology,the method of light-induced non-destructive detection of fungal diseases is expected to be widely used in the regular detection of fungal diseases.In terms of industrial production,the transaminase genes can be used as genetic targets for industrial production.