[1S01a] 10. ASPIRE - Part 2

3:30 PM - 3:45 PM JST(6:30 AM - 6:45 AM UTC)

[1ASPR-12] Contributions of Polygalacturonase-inhibiting Proteins (PGIPs) to Primary Cell Wall Degradation Enzymes during Xylem Vessel Differentiation

○Chaokun Huang¹ (1. Graduate School of Science, Department of Biological Sciences, The University of Tokyo (Japan))

Keywords:

Primary cell wall,Xylem differentiation,Polygalacturonase activity

[Purpose]
Cell wall remodeling is a critical process for xylem vessel functionality, and one of targets of remodeling is pectic depolymerization in the primary cell wall. Previously, the inhibitory mechanism between pathogen-derived polygalacturonases (PGs), pectin degradation enzymes, and plant polygalacturonase-inhibiting proteins (PGIPs) has been documented. However, the potential roles of plant PGIPs in regulating endogenous PGs during xylem development and tracheary element (TE) differentiation remain unclear. In this study, we characterized the spatial expression patterns, interaction with endogenous PGs, and physiological roles of PGIPs during xylem development, with a focus on the VND7-driven TE differentiation.
[Methode]
We combined reporter lines, TE induction systems, genetic analysis, and biochemical assays to investigate PGIP expression, localization, and function during xylem differentiation.
[Results]
Phylogenetic analysis revealed that three PGIPs form a single evolutionary clade which are highly conserved. The fluorescent tdTomato reporter lines elucidated the expression of PGIPs in the cytoplasm of leaf vasculature, but only PGIP1 specifically located in cell wall and apoplast. Ectopically induced TE in cotyledon demonstrated that PGIP1 is involved in the early stages of xylem vessel differentiation. Moreover, xylem vessel-specific overexpression of PGIPs reduces transport capacity, whereas loss-of-function mutants have a weaker effect on xylem transport. Cell wall polysaccharide profiling indicated that pectin-derived oligosaccharides (OGs) are released during TE differentiation. Consistent with an OG-triggered cell wall integrity (CWI) feedback, transcription levels of PGIPs were increased during in vivo TE induction, indicating that PGIP expression in neighboring undifferentiated cells contributes to limiting pectin degradation in plant tissues. In contrast, transcription levels of PGIPs were reduced during in vitro TE induction, suggesting that PGIPs act as negative regulators of xylem vessel formation. In addition, comparative transcriptome analysis of dexamethasone-induced T87 cells and phytohormone-induced cotyledons revealed that upregulation of PGIPs facilitates the downregulation of PG genes. The Bimolecular fluorescence complementation (BiFC) assay detected interactions between PGIPs and endogenous PGs at the cell wall /apoplastic regions. Total PG activity was increased in PGIP loss-of-function seedlings.
[Consideration]
This work extends the role of PGIPs beyond defense against pathogen-derived PGs and highlights PGIPs-mediated modulation of cell wall remodeling as an intrinsic component of the xylem differentiation program.
[Conclusion]
Our results support a model in which PGIPs act as endogenous modulators of PG-mediated pectin remodeling during xylem differentiation. The expression of PGIPs coupled with PG interaction signals suggested that development-immunity trade-off in CWI surveillance pathways.