The plasma membrane (PM) and the plant cell wall (CW) form together an exocellular continuum that acts as a dynamic barrier against environmental threats. The properties of the PM and the plant CW have been studied independently for several decades but increasing evidence indicates that a continuous dialogue between the PM and the CW takes place with the intracellular machinery playing the role of conciliator. LOOPIN is a multidisciplinary project combining genetics, molecular biology, cell biology and glycochemistry that will answer the pending key research question: What molecular negotiations underlie the reciprocal regulation between the PM and the CW? The original strategy of LOOPIN is based on my recent breakthrough results which suggest that (i) it exists an amazing diversity of PM-derived oligosaccharides (OS-like) and CW-derived oligosaccharides (OS) (ii) and that OS and OS-like may act as sugar-encoded messengers allowing the CW and PM external leaflet to communicate and adjust the plant cell response according to the environmental conditions. The challenge is to crack the sugar code involved in regulating CW/PM integrities and to understand how it controls the development. The objectives are (i) Set up biochemical and cell biology approaches to investigate the role of OS and OS-like in the CW/PM interplay, (ii) Identify biological active OS and OS-like involved in the CW/PM interplay and (iii) Decrypt the signalling pathways they trigger by selected OS- and OS-like. The approach of LOOPIN is unprecedented and should revolutionize our vision of how plant cells regulate the dynamics of the exocellular continuum.