Primary Researchs On The Suppression Of Cotton (Gossypium Hirsutum L.) Defense Response To Pathogen Of Alternaria Alternata Caused By Chilling Stress Pretreatment

Cotton premature leaf senescence restricted severely the production of cotton and caused seriousreduction in yield and quality of cotton. To reveal the molecular mechanism of cotton premature leafsenescence are important for further research and management of cotton premature leaf senescence.Previous studies showed that chilling stress is the key factor that cause of A. alternatia infection ofcotton, which leading of cotton Alternaria disease and leaf senescence. The detailed molecularmechanism of cotton premature leaf senscence is still unclear. In this paper, the molecular mechanism ofcotton premature leaf senescence was preliminary studied by microarray and virus induced genesilencing. The results show that chilling stress could suppress the cotton defense response, causedAlternaria disease, and eventually lead to cotton leaf senescence.The results were as follows:1. Chilling stess could suppress the cotton defense response. GO analysis show that the defenseresponse genes of the normal growth cotton were significantly up-regulated after inoculation, so thatAlternatia disease and cotton premature leaf senscence hardly occur. But the expression of the defenseresponse genes of the cotton chilling pre-treated after inoculation were suppressed, causing to seriousAlternatia disease and leading to cotton premature leaf senescence.2. There is a positive correlation between the development of Alternaria disease and ethyleneproduction. According to the result of microarray, the expression level of ethylene-related genes of thenormol gorth cotton after inoculation was not significantly changed, but the expression level of signaltransduction of ethylene-related genes (EIN2) of the cotton chilling stress pre-treated after inoculation6days of was significantly upregulated. So, ethylene content during Alternaria disease developmentpromoted by chilling stress pre-treatment were determined. Results of the study indicated that infectionof cotton leaves with A. alternata induced dramatic ethylene production, whereas insignificant ethyleneproduction increase only occurred at4-6days after inoculation. It may be assumed that the productionof ethylene increased caused the accelerated senescence progress.3. Cotton leaf crumple virus-induced gene silencing (VIGS) was used to silence ethylene relatedgenes and defense response related genes in XLZ13via targeting the fragment of GhMPK3gene,GhWDP2gene, GhWDP1gene, GhPAL gene, GhGML gene, GhDLP2gene and GhDLP1gene. A.alternatia was used to inoculate silence cotton plants. The results showed that, the disease index of wildtype XLZ13and VIGS with vector control plants were20.73，28.78， respectively. The disease index ofsilencing defense response related genes including GhMPK3gene, GhWDP2gene, GhWDP1gene,GhPAL gene, GhGML gene, GhDLP2gene and GhDLP1gene plants were82.82，77.32，73.16，66.61，54.50，47.31and46.41, respectively. Meanwhile, compared to the wild-type plants and VIGS withvector control plants, the H2O2content of the silencing defense response related genes plants weresignificantly increased, the DAB staining of the silencing defense response related genes plants hadobvious phenomenon. The results showed that silencing of the genes related to defense response could cause severe Alternatia disease. And the disease index of silencing ethylene related genes includingGhEIN2-1gene and GhEIN2-2gene plants were18.25，16.67, respectively. Compared to the wild-typeplants and VIGS with vector control plants, the disease index of silencing plants decreased. The resultsshow that silencing of the genes related to ethylene could reduce Alternatia disease.Chilling stress could suppress the cotton defense response, cause Alternaria disease and eventuallylead to cotton leaf senescence. And the production of ethylene increased caused the acceleratedsenescence progress. This research has demonstrated that molecular mechanism of cotton (Gossypiumhirsutum L.) premature leaf senescence. It could be expected that the understanding of the key factorscausing and promoting cotton leaf senescence would be helpful for taking appropriate managementsteps to prevent cotton premature leaf senescence.