Overexpression of Arabidopsis Plasmodesmata Germin-Like Proteins Disrupts Root Growth and Development  

Abstract

In plants, a population of non-cell-autonomous proteins (NCAPs), including numerous transcription factors, move cell to cell through plasmodesmata (PD). In many cases, the intercellular trafficking of these NCAPs is regulated by their interaction with specific PD components. To gain further insight into the functions of this NCAP pathway, coimmunoprecipitation experiments were performed on a tobacco (Nicotiana tabacum) plasmodesmal-enriched cell wall protein preparation using as bait the NCAP, pumpkin (Cucurbita maxima) PHLOEM PROTEIN16 (Cm-PP16). A Cm-PP16 interaction partner, Nt-PLASMODESMAL GERMIN-LIKE PROTEIN1 (Nt-PDGLP1) was identified and shown to be a PD-located component. Arabidopsis thaliana putative orthologs, PDGLP1 and PDGLP2, were identified; expression studies indicated that, postgermination, these proteins were preferentially expressed in the root system. The PDGLP1 signal peptide was shown to function in localization to the PD by a novel mechanism involving the endoplasmic reticulum-Golgi secretory pathway. Overexpression of various tagged versions altered root meristem function, leading to reduced primary root but enhanced lateral root growth. This effect on root growth was corrected with an inability of these chimeric proteins to form stable PD-localized complexes. PDGLP1 and PDGLP2 appear to be involved in regulating primary root growth by controlling phloem-mediated allocation of resources between the primary and lateral root meristems.

Genome-Wide Characterization and Expression Analysis of the Germin-Like Protein Family in Rice and Arabidopsis

“…Previous studies reported 29 AtGLP genes in Arabidopsis [18] and 41 OsGLP genes in rice [25]. We found three new GLP genes (AT1G74820, AT5G39100, AT5G61750) in Arabidopsis and two new GLP genes (Os01g14670, Os03g58990) in rice.…”

“…H 2 O 2 is an important component of plant defence responses, such as cell wall structure protein stiffening and lignification, as well as papillae formation [53]. In previous studies, GLP genes located on chromosome 8 in rice were reported to be the key disease-resistance genes [18,25]. Their orthologous GLP members in barley and grapevine are also implicated in basal defence responses [23,27], which suggests that the resistance conferred by the OsGLP genes on chromosome 8 is via a broad-spectrum, basal mechanism conserved among the Gramineae.…”

“…The overexpression of GLP genes in Arabidopsis and rice influenced the normal growth and development of plants [17,18]. Besides, GLP genes have different spatial and temporal expression characteristics in a variety of plants, which could affect the enzyme activities [3].…”

Versatility of germin-like proteins in their sequences, expressions, and functions

“…Various GLPs were known to be involved in growth and development of root tissues. An interesting study reported that two Arabidopsis thaliana orthologs, plasmodesmata germinlike proteins 1 and 2 (PD-GLP1 and PD-GLP2) were predominantly expressed in root tissues to control the root growth and development (Ham et al 2012). Overexpression of these two orthologs demonstrated reduced primary root growth but enhanced lateral root growth by regulating phloem-mediated allocation of resources between the primary and lateral root meristems.…”

Calmodulin-Mediated Signal Transduction Pathways in Arabidopsis Are Fine-Tuned by Methylation

“…Genes encoding GLPs are overexpressed in Prunus salicina fruit when treated with auxins (El-Sharkawy et al, 2010), and another member from Arabidopsis (GLP4) binds auxins in vitro (Yin et al, 2009). GLP10 has not been characterized to date, but it shows high similarity (more than 80% of the amino acid sequence) to plasmodesmata GLP (AT1G02335), which has been recently described to be involved in root development (Ham et al, 2012). Plants overexpressing plasmodesmata GLP are characterized by inhibition of primary root growth and compensatory increased development of lateral roots.…”