The Root Hair Specific SYP123 Regulates the Localization of Cell Wall Components and Contributes to Rizhobacterial Priming of Induced Systemic Resistance

Abstract

Root hairs are important for nutrient and water uptake and are also critically involved the interaction with soil inhabiting microbiota. Root hairs are tubular-shaped outgrowths that emerge from trichoblasts. This polarized elongation is maintained and regulated by a robust mechanism involving the endomembrane secretory and endocytic system. Members of the syntaxin family of SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) in plants (SYP), have been implicated in regulation of the fusion of vesicles with the target membranes in both exocytic and endocytic pathways. One member of this family, SYP123, is expressed specifically in the root hairs and accumulated in the growing tip region. This study shows evidence of the SYP123 role in polarized trafficking using knockout insertional mutant plants. We were able to observe defects in the deposition of cell wall proline rich protein PRP3 and cell wall polysaccharides. In a complementary strategy, similar results were obtained using a plant expressing a dominant negative soluble version of SYP123 (SP2 fragment) lacking the transmembrane domain. The evidence presented indicates that SYP123 is also regulating PRP3 protein distribution by recycling by endocytosis. We also present evidence that indicates that SYP123 is necessary for the response of roots to plant growth promoting rhizobacterium (PGPR) in order to trigger trigger induced systemic response (ISR). Plants with a defective SYP123 function were unable to mount a systemic acquired resistance in response to bacterial pathogen infection and ISR upon interaction with rhizobacteria. These results indicated that SYP123 was involved in the polarized localization of protein and polysaccharides in growing root hairs and that this activity also contributed to the establishment of effective plant defense responses. Root hairs represent very plastic structures were many biotic and abiotic factors can affect the number, anatomy and physiology of root hairs. Here, we presented evidence that indicates that interactions with soil PGPR could be closely regulated by signaling involving secretory and/or endocytic trafficking at the root hair tip as a quick way to response to changing environmental conditions.

PGPR‐mediated induction of systemic resistance and physiochemical alterations in plants against the pathogens: Current perspectives

“…Soluble proteins Nethylmaleimide-sensitive-factor attachment protein receptor (SNARE) was found effective in transportation, fusion of membranes of cargo-containing small shuttles, and referred to as vesicles, which target membranes in both exocytic and endocytic pathways [38]. Syntaxin of plant proteins (SYP), such as SYP123 and SYP132, and SNARE proteins were reported to be expressed specifically in the root hairs and were found to play roles in the correct localization and dispersion of defense-related proteins such as PRP3 (proline-rich protein 3) in the cell wall, thus establishing an effective plant defense against diseases [39]. The defense genes such as PR1, PDF1.2, MYB72, and MYC2 showed manifold expression on ISRpriming [40,41].…”

“…The transgenic plants, which show an overexpression of SYP123, have the ability to increase the expression of ISR-priming genes as compared with wildtype plants in response to rhizobacteria Pseudomonas spp. [39,42].…”

SCYL2 Genes Are Involved in Clathrin-Mediated Vesicle Trafficking and Essential for Plant Growth

“…It was reported that the function of root hair tiplocalized proteins, such as RHO-RELATED PROTEIN FROM PLANTS2 (ROP2), ROOT HAIR DEFECTIVE2 (RHD2), RAB GTPASE HOMOLOG A4B (RABA4B), SYNTAXIN OF PLANTS123 (SYP123), PRO-RICH PROTEIN3 (PRP3), and CSLD3, is important for proper root hair tip growth (Jones et al, 2002;Foreman et al, 2003;Preuss et al, 2004;Park et al, 2011;Ichikawa et al, 2014;Rodriguez-Furlán et al, 2016). To understand the root hair tip growth pathways in which SCYL2B functions, Col-0 and scyl2b mutants were transformed with GFP fusion constructs, including ROP2, RHD2, RABA4B, SYP123, PRP3, and CSLD3 genes, whose expression is driven by the EXPANSIN A7 (EXPA7) promoter, a root hair-specific promoter (Kim et al, 2006).…”

Membrane Trafficking in Plant Immunity

“…PEN1 forms a SNARE complex with SNAP33 and VAMP721/722 to direct focal secretion of defense molecules (Collins et al, 2003; Kwon et al, 2008). Another SYP1 member, SYP123, accumulates at the tip of growing root hairs and is necessary for polarized trafficking of cell wall components and induced systemic resistance (ISR) triggered by rhizobacteria in Arabidopsis (Rodriguez-Furlan et al, 2016). SYP132 appears to be central for multiple defense responses because silencing of a SYP132 ortholog in N. benthamiana resulted in impaired basal resistance, ETI and SAR (Kalde et al, 2007).…”