This article addresses two architectural challenges associated with managing and orchestrating open radio access network (O-RAN) slice subnets within the service management and orchestration (SMO) Framework. The first challenge involves unifying the components and interfaces of the O-RAN Alliance, Third Generation Partnership Project (3GPP), and European Telecommunications Standards Institute (ETSI) to enhance the capabilities of the SMO Framework regarding the management and orchestration (M&O) of O-RAN slice subnets and their required resources. The objective of this unification is to eliminate ambiguity in the interaction, interworking, and integration of various standards within a unified SMO Framework and to enable it to leverage the latest specifications. The second challenge entails facilitating standard-compliant interoperability among the components of the three modules by proposing two logical functions and their interfaces within the SMO Framework. This interoperability is intended to enable the components and interfaces of the O-RAN architecture to influence the decisions made by the 3GPP and ETSI components and interfaces concerning O-RAN slice subnets. It will also allow the 3GPP and ETSI components and interfaces to improve their capabilities by utilizing the features and services of the O-RAN architecture.