Direct evidence for a new mode of plant defense against insects via a novel polygalacturonase-inhibiting protein expression strategy

Abstract

<jats:p>Plant cell wall-associated polygalacturonase-inhibiting proteins (PGIPs) are widely distributed in the plant kingdom. They play a crucial role in plant defense against phytopathogens by inhibiting microbial polygalacturonases (PGs). PGs hydrolyze the cell wall polysaccharide pectin and are among the first enzymes to be secreted during plant infection. Recent studies demonstrated that herbivorous insects express their own PG multi-gene families, raising the question whether PGIPs also inhibit insect PGs and protect plants from herbivores. Preliminary evidence suggested that PGIPs may negatively influence larval growth of the leaf beetle Phaedon cochleariae (Coleoptera: Chrysomelidae) and identified BrPGIP3 from Chinese cabbage (Brassica rapa ssp. pekinensis) as a candidate. PGIPs are predominantly studied in planta because their heterologous expression in microbial systems is problematic and instability and aggregation of recombinant PGIPs has complicated in vitro inhibition assays. To minimize aggregate formation, we heterologously expressed BrPGIP3 fused to a glycosylphosphatidylinositol (GPI) membrane anchor, immobilizing it on the extracellular surface of insect cells. We demonstrated that BrPGIP3_GPI inhibited several P. cochleariae PGs in vitro, providing the first direct evidence of an interaction between a plant PGIP and an animal PG. Thus, plant PGIPs not only confer resistance against phytopathogens, but may also aid in defense against herbivorous beetles.</jats:p>

Dampening the DAMPs: How Plants Maintain the Homeostasis of Cell Wall Molecular Patterns and Avoid Hyper-Immunity

“…OGs antagonize auxin (Branca et al, 1988;Bellincampi et al, 1995) by inhibiting the transcription of auxin-induced genes belonging to the IAA and SAUR families as well as the activity of the auxinresponsive promoter DR5 (Savatin et al, 2011). During microbial infections, the accumulation of OGs is facilitated by the interaction of microbial polygalacturonases (PGs) with specific PG-inhibiting proteins (PGIPs; Kalunke et al, 2015;Haeger et al, 2020). Notably, the transgenic expression of a PGIP-PG chimera referred to as the "OG-machine" is able to produce in vivo endogenous OGs, enhancing Arabidopsis resistance against Botrytis cinerea, Pectobacterium carotovorum, and Pseudomonas syringae (Benedetti et al, 2015).…”

Engineering of Polygalacturonase-Inhibiting Protein as an Ecological, Friendly, and Non-toxic Pest Control Agent

“…Although we were successful in demonstrating the interactions between PGIPs and PGs using a Y2H system, some previous studies report that PGIPs are difficult to express in soluble in microbial system. This could be due to a number of factors, such as protein instability or an aggregation of recombinant PGIPs (Haeger et al, 2020). Nevertheless, in this study we were able to reconstitute the PG-PGIP interaction using a Y2H system and identified a method to secrete functional PGIP from yeast into the medium.…”

“…Here, we investigate the potential of using engineered PvPGIP2 as a fungal growth inhibitor. We utilized Saccharomyces cerevisiae as a microbial expression system, which has benefits such as the lack of background PGIP activity and a fast turnover time (Haeger et al, 2020). We reproduced previously reported interactions between PvPGIP2 and various PGs in a yeast two hybrid (Y2H) system, thus validating it as a handy approach to estimate PvPGIP2 activity.…”

Host Cell Wall Damage during Pathogen Infection: Mechanisms of Perception and Role in Plant-Pathogen Interactions

“…Notably, P. sojae in turn has evolved a paralogous decoy protein (PsXLP1) that has no enzymatic activity but interacts more tightly with GmGIP1 than PsXEG1, thus preventing the inhibition of its hydrolytic activity [ 111 ]. The production of decoy pseudoenzymes to evade inhibition of CWDEs might be more widespread than currently acknowledged [ 112 ].…”