Study On The Disease Resistance Mechanism Of Betula Platyphylla MiR156-SPL In Response To Alternaria Alternata

Leaf blight is a common disease of white birch（Betula platyphylla）seedlings caused by fungi such as Alternaria alternata,which severely affects the growth of white birch.In a pre-vious study,it was found that leaf blight infection was more severe in birch seedlings overex-pressing Bpmi R156 under natural environment.In this study,we used overexpressed Bpmi R156birch plants as materials to analyze the physiological and gene expression changes during the disease susceptibility of the plants,to clarify the target genes of Bpmi R156 that regulate the process of plant resistance response,and to analyze the mechanism of Bpmi R156-SPL that reg-ulates the disease resistance of birch.The results of the study are as follows:1.Inoculation of tissue culture rooted seedlings of Bpmi R156 overexpressing birch strains with the A.alternata.showed that:the disease resistance of transgenic birch strains was re-duced;and the activities of resistance-related enzymes such as PPO changed significantly;Gene quantification of Bp SPLs during A.alternata stress treatment showed that Bp SPL6 and Bp SPL16 gene expression was regulated by Bpmi R156.2.Transcriptomic analysis revealed that 2544 differentially expressed genes,including Bp WRKYs,were screened in the wild type compared with transgenic strains.3.Transgenic birch with Bp SPL6,Bp SPL16 were inoculated with A.alternata.for 0,3,5,7 and 9 d.The physiological and biochemical indices and the expression of Bp WRKYs genes were analyzed,and the results showed that the disease resistance of the overexpression strain of Bp SPL6 was higher than that of the wild-type plants,and the disease resistance of the sup-pression expression strain of Bp SPL6,Bp SPL16 was significantly reduced.The activities of H₂O₂,SOD,CAT,MDA,PPO and PAL of each transgenic strain during infestation changed continuously with the extension of stress treatment time,and different transgenic strains saw significant differences in the changes of enzyme activities.All three Bp WRKYs genes screened by transcriptome were induced to be expressed during pathogen infestation,and there were dif-ferences in the change trends.4.KEGG enrichment analysis of differential genes in leaves of transgenic plants overex-pressing and repressing Bp SPL6 showed that the shared differential genes between wild-type and transgenic strains were mainly enriched in plant-pathogen interactions,plant hormone sig-nal transduction,MAPK signaling transduction and phenylpropanoid biosynthesis.A total of286 differentially expressed genes were screened for wild-type and overexpression strains.424differentially expressed genes were screened between wild-type and suppression strains.Based on the expression pathway map of plant disease-course-related genes,three Bp WRKYs genes were found to be differentially expressed in transgenic strains.The sequences of Bp SPLs gene recognition sites in the promoters of Bp WRKYs genes were constructed into p HIS2-WRKY re-porter vectors,and the self-activation activity of Bp WRKYs was detected by self-activation as-say.In summary,this study found that Bpmi R156 overexpression and Bp SPL6,Bp SPL16 sup-pression expression enhanced the susceptibility of birch plants to A.alternata inoculation;dur-ing pathogen infestation,Bp SPL6 and Bp SPL16 genes acted downstream of Bpmi R156 gene and participated in the immunization process of birch against A.alternata.