Towards understanding of plasmodesmal association and regulation using Plasmodesmata-Located Protein 5 as a model
Date
2017
Authors
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Publisher
University of Delaware
Abstract
Plasmodesmata (PDs) mediate intercellular communication by facilitating cell- to-cell exchange of soluble molecules in plants. Despite a growing number of proteins are identified to associate with PD and affect PD permeability, not much is known about how they are targeted to PD and regulate PD function. Arabidopsis Plasmodesmata-Located Protein 5 (PDLP5), a receptor-like type I transmembrane protein associated with PD and restricts PD permeability. PDLP5 expression is controlled by a salicylic acid (SA)-dependent signaling pathway, and functional PDLP5 is required for the immunity. However, it is not understood how PDLP5 associates with PD and how it restricts PD permeability during defense responses. To gain insight into the mechanisms underlying PDLP5 targeting and function, a mutagenesis approach in combination with various functional analyses was taken. Subcellular localization studies of the mutant constructs fused to fluorescent proteins revealed that while the presence of transmembrane domain (TMD) is important for plasmodesmal membrane association, no specific sequence within the TMD is required for its targeting to PD. Instead, we found that other domains differentially contribute to PD localization and that the TMD is responsible for homo- or heteromeric interactions with other PDLP members. Functional analyses using fluorescent dye and GFP movement assays indicated that the extracellular domain is essential for PDLP5 function. Analyzing Arabidopsis mutants that are impaired in SA biosynthetic or signaling pathways such as eds1, ics1 or npr1, using PD permeability assays and PD callose quantifications showed that, SA accumulation is critical for PDLP5-mediated PD-callose deposition and -closure during microbial pathogen infection.
Description
Keywords
Plasmodesmata, Protein 5