Leptosphaeria maculans interacts with its host Brassica napus according to gene-for-gene concept, where the recognition of the only molecule (pathogen´s effector) by its corresponding partner (product of plant resistance gene) protects the plant against disease development. However, the fungus is able to avoid recognition by mutation events, partial or complete deletion of the avirulence gene. Eleven L. maculans avirulence genes were genetically mapped and at least 3 were cloned up to date, however the functions of the effector proteins for which they code are still unknown. AvrLm4-7 belongs among the few cloned effectors and is special for its dual specificity to products of B. napus resistance genes Rlm4 and Rlm7. By a single amino acid change AvrLm4-7 escapes recognition by Rlm4, but is still recognized by Rlm7. Moreover, absence of the functional AvrLm4-7 allele is linked with decreased aggressiveness suggesting that the effector is important for L. maculans fitness. The question remains: why? After the recognition of invading agent plant signal transduction pathways mediated by plant hormones play a pivotal role in induction of appropriate defence responses. Although more is known about bacterial effectors, recently has been shown that also fungal effectors can affect the plant defence signalling in favour of the pathogen.We investigated the effect of AvrLm4-7 on defence signalling in oilseed rape. Using RT-qPCR we examined the level of transcription of previously characterized marker genes of salicylic acid, jasmonic acid, abscisic acid and ethylene signalling pathways in a susceptible cultivar of B. napus inoculated by L. maculans isolates carrying or lacking AvrLm4-7. We found that salicylic acid and ethylene-specific marker genes are supressed during the infection by the isolate carrying the AvrLm4-7 effector gene. Moreover, the presence of AvrLm4-7 seems to influence the formation of reactive oxygen species in infected cotyledons. Although it is still long way to go to uncover the function of AvrLm4-7 effector, we contributed to narrow the field of search for possible AvrLm4-7 target proteins.