Filamentous pathogens such as the oomycete Phytophthora infestans infect plants by developing specialized structures termed haustoria inside the host cells. Haustoria are thought to enable the secretion of effector proteins into the plant cells. Haustorium biogenesis, therefore, is critical for pathogen accommodation in the host tissue. Haustoria are enveloped by a specialized hostderived membrane, the extrahaustorial membrane (EHM), which is distinct from the plant plasma membrane. The mechanisms underlying the biogenesis of the EHM are unknown. Remarkably, several plasma membrane-localized proteins are excluded from the EHM, but the remorin REM1.3 accumulates around P. infestans haustoria. Here, we used overexpression, colocalization with reporter proteins, and superresolution microscopy in cells infected by P. infestans to reveal discrete EHM domains labeled by REM1.3 and the P. infestans effector AVRblb2. Moreover, SYNAPTOTAGMIN1, another previously identified perihaustorial protein, localized to subdomains that are mainly not labeled by REM1.3 and AVRblb2. Functional characterization of REM1.3 revealed that it is a susceptibility factor that promotes infection by P. infestans. This activity, and REM1.3 recruitment to the EHM, require the REM1.3 membrane-binding domain. Our results implicate REM1.3 membrane microdomains in plant susceptibility to an oomycete pathogen.

Shared systems in leaf development The long, narrow leaves of grasses look rather different from the often shorter, flatter leaves of eudicot plants. Richardson et al . combined developmental genetics and computational modeling to reveal that these two types of leaves, which are widely separated by evolution, have more in common than expected. Expression of similar patterning genes in the primordial zone is confined to a wedge for the eudicot leaf but expanded to concentric domains in the grass leaf, driving development of the cylindrical, encircling sheath characteristic of grass leaves. Addition or removal of gene expression in a marginal zone contributes to the development of the broader leaf characteristic of eudicots. Thus, grass and eudicot leaves are diversified elaborations of shared toolkits. —PJH