| The capsicum Phytophthora is one of the most serious diseases that endanger the pepper production.Although some of the existing methods for controlling the Phytophthora are effective,not only are they not ideal,but also could lead to various environmental problems.More and more attention has been paid to the use of endophytes to improve controlling efficiency and reduce environmental pollution.Previous experiments have proved that two strains of endophytic bacteria DLJ1 and SZ5,which can secrete ACC deaminase,can promote the growth of pepper seedlings and increase the yield of pepper when being inoculated at germination stage;and DLJ1 treatment can also increase the resistance of plants to P.capsici.The RNA-seq technology was used in this paper to compare the differences of gene expressions in plants under diverse treatments,and tried to analysis of the growthpromoting mechanism of two endophytes and the resistance-promoting effects of DLJ1 to P.capsici.Results are as follows:First,the effect that DLJ1 treatment can significantly improve the resistance of plants to P.capsici and SZ5 treatment brought little effect was affirmed.Then,the pepper seeds were inoculated with DLJ1 or SZ5 at germination stage,and chal enged with P.capsici at seedling stage.Leaves with the same position were sampled at the early stage of disease,and their transcriptomes were extracted and sequenced.The quality of transcriptome sequencing was qualified and could be used for further analysis.The analysis on gene expressions of plants from three treatments without inoculation of P.capsici showed that,both treatments with DLJ1 and SZ5 promoted such genes’ expression down-regulated as ethylene biosynthesis,signal transduction,and resistance-related genes,while the changes caused by DLJ1 treatment were greater.This is beneficial for plants to use limited energy for growth and development.In addition,DLJ1 treatment also promoted the expression of genes related with antioxidant enzymes,disease-related proteins and photosynthesis,which ultimately led to a more significant improving effect on plant growth.After inoculated with P.capsici,the expression of ethylene signal transduction factors and defense related genes decreased,and the expression of photosynthetic related genes increased in the control.This indicated that the resistance of pepper plants to P.capsici is low.When invaded with P.capsici,the expression of ethylene transcription factors and resistance-related genes was enhanced,while the expression of photosynthetic related genes was decreased in the DLJ1 pre-vaccinated group.The expression of resistance-related genes in SZ5 group was similar to that in DLJ1 group,but the expression of ethylene signal transduction factor in SZ5 group was not significantly up-regulated.The results of the above transcriptome analysis were verified by qPCR experiments.Accordingly,the possible growth-improving mechanism of DLJ1 and SZ5,and the possible enhancing resistance mechanism of plants to P.capsici were summarized as follows:Inoculation of DLJ1 at germination stage reduces the seedlings’ resistance,which is not only facilitated the colonization of endophytes,but also helps the plants to use limited energy for photosynthesis and growth.SZ5 has a similar effect,but the changes in the number and the expression of genes involved are relatively smal,which leads to its relatively weak growth-promoting effect.When plants were defiantly infected with P.capsici,the control group and the SZ5-preinoculated group show little resistance;the expression of “ethylene signal transduction transcription factor"increased rapidly,which leads to the expression of a series of resistance-related genes in the DLJ1-preinoculated treatment.At the same time,the expression of photosynthesis-related genes was inhibited and plant resistance-related genes were enhanced.It was concluded that the up-regulation of ethylene signal transduction factor might be the key factor for DLJ1 to enhance plant resistance to P.capsici. |
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