Expression domain analysis of four members of the plasmodesmata-localized protein family in Arabidopsis
Date
2016
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
There are two modes of cell-to-cell communication between plant cells: the apoplastic and symplastic pathways. The apopolastic pathway involves endocytosis and exocytosis, whereas, the symplastic pathway involves movement through plasmodesmata (PD). PD are channels that directly connect the cytoplasms of neighboring cells and allow for the symplastic trafficking of proteins, RNA and other small molecules. PD, over the years, have been implicated in plant growth, development, survival and innate immune responses. Protein analysis of cell wall extractions identified a family of proteins called Arabidopsis PD-localized protein (PDLP), named for their association with PD. There are 8 type-I membrane receptor like proteins in the PDLP family. PDLP1 and PDLP5 have been shown to regulate plasmodesmal aperture. Here, the expression domains and patterns of four PDLP members, PDLP4, 6, 7 and 8 were investigated using the yellow fluorescent protein and/or β-glucoronidase reporter systems. The results of this study distinct tissue and cell specific expression patterns of these members. PDLP4 promoter was active in primary and lateral roots, both in the mature endodermal cells with developed casparian strips and the lateral root cap. PDLP6 promoter was active in the shoot apical meristem. It was also transiently induced in the primary root vasculature and root tip. PDLP7 promoter was active in the companion cells of cotyledons and young true leaves. As well as in the primary root, specifically phloem pole pericycle, companion cells and the columella root cap. Similar to PDLP7, PDLP8 promoter was active in the vasculature of cotyledons and roots, including the companion cells and the phloem pole pericycle. The expression patterns of PDLP4 and PDLP7 were quite exciting given that no information is known about the role of PD in that tissue. Thus, analysis of the PDLP4 and PDLP7 genes was carried out using auxin treatments of the PDLP4pro:GUS and PDLP7pro:GUS lines and phenotyping the transgenic knockout lines for each gene. Observation and quantification of primary root growth of individual mutants revealed significant differences between the growth of pdlp7-1 lines and WT plants. Gravitropic assays coupled with histochemical assays revealed a role for PDLP4 and PDLP7 in lateral root emergence. While confocal imaging of mutants revealed abnormal root cap cell morphology and subsequently hindered sloughing of root cap cells, similar in phenotype to the SOMBRERO, BEARSKIN 1 and BEARSKIN 2 (SMB, BRN1 and BRN2) knockouts. SMB, BRN1 and BRN2 are NAC domain transcription factors involved in cell wall modifications. Based on expression patterns, auxin responsiveness, and knockout line phenotypes, I propose a mechanism for lateral root propagation in phloem pole pericycle cells in pdlp7-1 lines. Additionally, a role for PDLP7 and PDLP8 in floral transitioning. And lastly, a method to study symplastic movement of the transcription factor WUSCHEL by regulating PD aperture within the shoot apical meristem using PDLP6.
Description
Keywords
Biological sciences, Callose, PDLP, PDLP4-1, PDLP5, PDLP7-1, Plasmodesmata