Specific Targeting of a Plasmodesmal Protein Affecting Cell-to-Cell Communication

TLDR

Plasmodesmata are cytoplasmic channels essential for plant growth, development, and defense, yet the determinants that target proteins to these structures remain largely unknown. The authors aim to identify a new family of plasmodesmata‑localized proteins (PDLP1) and to investigate whether the first member, PDLP1a, can modulate cell‑to‑cell trafficking. They study PDLP1a, a type I membrane receptor‑like protein, and demonstrate that its altered expression alters intercellular transport. PDLP1a is delivered to plasmodesmata via a Brefeldin A‑sensitive, COPII‑dependent secretory route, with its C‑terminus cytoplasmic and N‑terminus apoplastic; its single transmembrane domain alone suffices for targeting, enabling heterologous protein delivery and revealing a novel trafficking mechanism that expands tools for plasmodesmal research.

Abstract

Plasmodesmata provide the cytoplasmic conduits for cell-to-cell communication throughout plant tissues and participate in a diverse set of non-cell-autonomous functions. Despite their central role in growth and development and defence, resolving their modus operandi remains a major challenge in plant biology. Features of protein sequences and/or structure that determine protein targeting to plasmodesmata were previously unknown. We identify here a novel family of plasmodesmata-located proteins (called PDLP1) whose members have the features of type I membrane receptor-like proteins. We focus our studies on the first identified type member (namely At5g43980, or PDLP1a) and show that, following its altered expression, it is effective in modulating cell-to-cell trafficking. PDLP1a is targeted to plasmodesmata via the secretory pathway in a Brefeldin A-sensitive and COPII-dependent manner, and resides at plasmodesmata with its C-terminus in the cytoplasmic domain and its N-terminus in the apoplast. Using a deletion analysis, we show that the single transmembrane domain (TMD) of PDLP1a contains all the information necessary for intracellular targeting of this type I membrane protein to plasmodesmata, such that the TMD can be used to target heterologous proteins to this location. These studies identify a new family of plasmodesmal proteins that affect cell-to-cell communication. They exhibit a mode of intracellular trafficking and targeting novel for plant biology and provide technological opportunities for targeting different proteins to plasmodesmata to aid in plasmodesmal characterisation.