In adapting to their changing environment, plants need to balance the integration of signals stemming from biotic and abiotic factors and regulatory mechanisms governing growth and development. Within this context, two factors will be considered for my project: 1) the colonization of A. thaliana roots by the beneficial microbe Bacillus sp. as a biotic environmental stimulus and 2) the plant specific family of ROP GTPases, which serve as molecular switches regulating various processes surrounding cellular development and metabolism. Using high resolution microscopy coupled with 3D printed growth chambers, we for one plan to elucidate the effects of Bacillus sp. colonization on root hair morphology and decipher its significance for the microbial association. On the other hand, we will investigate potentially novel interaction partners of the ROP GTPase ROP2 and examine their importance in the interaction with Bacillus sp. In summary, this project aims to understand how signals deriving from Bacillus sp. colonization are integrated into changes in growth and development in the roots of A. thaliana and to which extent signaling hubs such as ROP GTPases are involved.