Biotrophic fungi for which the HR response is a viable resistance mechanism form invaginations in host cell membranes known as haustoria. The fungi secrete effectors into the extrahaustorial matrix and these effectors are transported into host cells, although the exact mechanism of such translocation is not known (in some oomycetes, there are consereved amino acid sequences found to be necessary for such translocation). The HR, much like in bacteria, is initiated by a signaling cascade pathway leading to transciptional activation of HR-related genes. This cascade begins with host perception of effectors by host resistance genes.