Abstract
Systemic acquired resistance (SAR) induction is one of the primary defence mechanisms of plants against a broad range of pathogens. It can be induced by infectious agents or by synthetic molecules, such as benzo(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH). SAR induction is associated with increases in salicylic acid (SA) accumulation and expression of defence marker genes (e.g., phenylalanine ammonia-lyase (PAL), the pathogenesis-related (PR) protein family, and non-expressor of PR genes (NPR1)). Various types of pathogens and pests induce plant responses by activating signalling pathways associated with SA, jasmonic acid (JA) and ethylene (ET). This work presents an analysis of the influence of BTH and its derivatives as resistance inducers in healthy and virus-infected plants by determining the expression levels of selected resistance markers associated with the SA, JA, and ET pathways. The phytotoxic effects of these compounds and their influence on the course of viral infection were also studied. Based on the results obtained, the best-performing BTH derivatives and their optimal concentration for plant performance were selected, and their mode of action was suggested. It was shown that application of BTH and its derivatives induces increased expression of marker genes of both the SA- and JA-mediated pathways.
Highlights
Plants are organisms with limited mobility, which determines their ability to defend against pathogens and pests
Reduced accumulation of viral RNA in the apical leaf was observed for plants challenged with all the resistance inducers tested, with the lowest level of viral RNA accumulation observed for plants pre-treated with BTHWA (approximately 36,000 times less viral RNA in plants challenged with this compound than in water-treated plants with virus inoculation (Figure 1, Plant set 7)) and [Chol][BTHCOO]
We are almost helpless against viral infections, as these pathogens are specific in their action and closely associated with host plants; there is no direct method to fight them without harming the plants
Summary
Plants are organisms with limited mobility, which determines their ability to defend against pathogens and pests. When comparing untreated virus-infected plants to virus-infected plants treated with BTH or its derivatives, a significant increase in PR-1b gene expression on each analysed day for all the tested inducers was observed (Figure S1a,b and Table S4) This comparison showed statistically significant upregulation of the ER and PI II genes (4 hpi), CTR, ER and NPR1 (5 dpi) and all genes except for the PAL gene (9 dpi) in BTHWA- and [Chol][BTHCOO]-treated plants. A multivariate ANOVA test was used to confirm the statistical significance of gene expression levels after comparison of three independent variables (viral infection, resistance inducer treatment (BTHWA and [Chol][BTHCOO]), and time point post infection) For both of these BTH derivatives, all results obtained were statistically significant (Table S7)
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