[Maria-discuss] MariaDB Galera Cluster version 10.0 incompatible with the version 5.5

Hi All, I'm new in the clustering, after installed 4 nodes with 3 having version 10.0 and another with version 5.5, this last did not want to join the cluster until I upgrade it to version 10.0. My question is, they is an incompatibility between the two versions? Thanks