| Sorghum is one of the most important grain crops in the world.It is also an important raw material for forage,industry and energy development.The sugarcane aphid,Melanaphis sacchari,is one of the main pests infecting sorghum.Due to its strong fecundity,it has seriously reduced the yield and quality of sorghum.Plant hormones play an important role in plant defense system against pathogens / insects.Salicylic acid(SA)can induce plant resistance to various pathogens / insects,and excessive accumulation of SA can interfere with auxin(IAA)responses.Gene A and B at RMES1 locus are genes conferring resistance to Melanaphis sacchari.However,the mechanism of how they regulate hormone to defend aphids is not clear.In this study,the sorghum aphid-resistant variety HN16(WT,including gene A and B at RMES1 locus),aphid-susceptible mutant asm1(gene B mutated at RMES1 locus)and aphid-susceptible mutant asm2(gene A mutated at RMES1 locus)were used as research materials.By analyzing the transcriptome data and the content changes of endogenous hormones in the process of aphid feeding,and combined with the external hormone experiment,the change law of SA / IAA signal pathway in the aphid-resistance reaction mediated by RMES1 have be analyzed,which can provide a theoretical basis for sorghum resistance breeding.The main results are as follows:1.Venn diagram analysis found that there were a large number of differentially expressed genes between WT and asm1 / asm2.KEGG enrichment analysis and heat map analysis found that a total of 33 SA and IAA pathway genes were enriched.Focus on SA and IAA pathway genes and verify their expression levels.The results are basically consistent with transcriptome analasis.The assay of endogenous hormones content during aphid feeding found that SA accumulation increased and IAA accumulation decreased at RMES1-mediated aphid-resistance responses.It shows that SA and IAA pathways are changed and activated in the aphid resistance mediated by RMES1.2.After external application of SA and resistance identification,it was found that SA positively regulated the resistance response of sorghum to aphids.The positive regulation of SA was further proved by the analysis of the expression of marker gene of SA signal pathway.By analyzing the expression pattern of marker gene in other hormone pathways,it is speculated that there is an interaction between SA and CK / IAA in the aphid resistance mediated by RMES1.After external application of IAA and resistance identification,it was found that IAA negatively regulated the resistance response of sorghum to aphids.And the expression pattern analysis of the marker gene of IAA signaling pathway further proved the negative regulatory response of IAA,and the mutation of gene A and B at RMES1 made this negative response be further enhanced.3.After external application of SA / IAA and resistance identification,it was found that there was an interaction between SA and IAA and the SA signaling pathway was activated while the IAA pathway was inhibited in the aphid resistance mediated by RMES1.And the analysis results of the expression of marker genes in the SA and IAA pathways were consistent with the resistance identification,which further confirmed the interaction between SA and IAA.4.Compared with the mutant,the expression of Sb PAL gene in WT was increased significantly under the condition of external application of SA and during the feeding process of aphids,while the expression of Sb ICS1 gene was decreased significantly.And compared with the mutant,the enzymatic activity level of PAL in WT was increased significantly,while the activity of ICS1 did not change significantly.Therefore,it is speculated that the SA is synthesized through the phenylpropane pathway in the aphid-resistace mediated by RMES1.5.The results of bacterial colony PCR identification,plasmid double-enzyme digestion identification and sequencing showed that the VIGS expression vector of A and B gene at RMES1 was successfully constructed and can be used in the next VIGS experiment. |
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