Plasma accelerators driven by advanced laser sources and/or compact electron linacs are key components for the next generation of green and sustainable research infrastructures. We propose a project on the development of "Plasma Accelerator systems for Compact Research Infrastructures" (PACRI), which will develop highly important and ground-breaking plasma accelerator technologies for Europe's future research infrastructures (RI). The specific objectives of PACRI are: - The development of high repetition rate plasma modules, as required for the EuPRAXIA ESFRI project, capable of extending its scientific scope from high average brightness radiation sources to high energy physics. - Improving the performance of normal conducting accelerator technology for X-band linacs, paving the way for high repetition rate operation (up to kHz) with a focus on efficiency and power consumption. - The development of key laser components required to scale up high power, high repetition rate laser technology as required by the EuPRAXIA and ELI ESFRI research infrastructures. The achievement of the PACRI objectives will enable the production of unique particle and photon beams with a wide range of applications in ultrafast science, high precision medical imaging, materials diagnostics, medical treatment and, in the longer term, the development of future compact colliders. These developments will be used for future resource-efficient upgrades of existing RIs at INFN, Elettra, CERN, CNR, CNRS, DESY, ELI, GSI/FAIR and UKRI. In addition, PACRI will support the implementation of ESFRI's EuPRAXIA distributed research facility by consolidating its sites and centres of excellence being developed under the ongoing EuPRAXIA_PP project. It will fund the development of some technical prototypes that are crucial for the implementation of the EuPRAXIA project and other European Research Infrastructures (e.g. enabling major upgrades to the ELI-Beamlines facility).