This call aims to support the integration of post-quantum cryptography (PQC) algorithms into Public Key Infrastructures (PKIs) to ensure secure, efficient, and compatible migration from current cryptographic standards. It focuses on developing new cryptographic combiners, testing hybrid certificates in various protocols, and improving open-source libraries for certificate management, validation, and transparency. Proposals should address key management, security, performance, and backward compatibility across critical sectors while ensuring smooth coexistence of pre-quantum and post-quantum systems. The call encourages the creation of clear transition procedures and collaboration among diverse PKI stakeholders, including researchers, developers, certification authorities, and end-users, to build resilient and future-proof PKI ecosystems.