Abstract
Polygalacturonase-inhibiting protein (PGIP), belonging to a group of plant defence proteins, specifically inhibits endopolygalacturonases secreted by pathogens. Herein, we showed that purified GhPGIP1 is a functional inhibitor of Verticillium dahliae and Fusarium oxysporum f. sp. vasinfectum, the two fungal pathogens causing cotton wilt. Transcription of GhPGIP1 was increased in cotton upon infection, wounding, and treatment with defence hormone and H2O2. Resistance by GhPGIP1 was examined by its virus-induced gene silencing in cotton and overexpression in Arabidopsis. GhPGIP1-silenced cotton was highly susceptible to the infections. GhPGIP1 overexpression in transgenic Arabidopsis conferred resistance to the infection, accompanied by enhanced expression of pathogenesis-related proteins (PRs), isochorismate synthase 1 (ICS1), enhanced disease susceptibility 1 (EDS1), and phytoalexin-deficient 4 (PAD4) genes. Transmission electron microscopy revealed cell wall alteration and cell disintegration in plants inoculated with polygalacturonase (PGs), implying its role in damaging the cell wall. Docking studies showed that GhPGIP1 interacted strongly with C-terminal of V. dahliae PG1 (VdPG1) beyond the active site but weakly interacted with C-terminal of F. oxysporum f. sp. vasinfectum (FovPG1). These findings will contribute towards the understanding of the roles of PGIPs and in screening potential combat proteins with novel recognition specificities against evolving pathogenic factors for countering pathogen invasion.
Highlights
Polygalacturonase-inhibiting protein (PGIP), belonging to a group of plant defence proteins, inhibits endopolygalacturonases secreted by pathogens
The predicted protein displayed the typical topology of previously described PGIPs, which included a 22-amino acid signal peptide for secretion, an N-terminal domain, an leucine-rich repeat (LRR) domain composed of 10 imperfect modules characterized by an extracytoplasmic type LRR consensus sequence, and a C-terminal domain
Phylogenetic analysis of GhPGIP1 was performed by constructing a phylogenetic tree that consisted of several main branches (Fig. 2), in which cotton PGIP was observed to have a high degree (80%) of amino acid identity with PGIPs from Arabidopsis[15], suggesting that they might have similar features and functions
Summary
Polygalacturonase-inhibiting protein (PGIP), belonging to a group of plant defence proteins, inhibits endopolygalacturonases secreted by pathogens. Resistance by GhPGIP1 was examined by its virus-induced gene silencing in cotton and overexpression in Arabidopsis. GhPGIP1 overexpression in transgenic Arabidopsis conferred resistance to the infection, accompanied by enhanced expression of pathogenesis-related proteins (PRs), isochorismate synthase 1 (ICS1), enhanced disease susceptibility 1 (EDS1), and phytoalexindeficient 4 (PAD4) genes. Polygalacturonase-inhibiting protein (PGIP) is a cell wall-binding protein that effectively and binds with PGs and inhibits further invasion of pathogens[7]. Transgenic tobacco plants expressing Capsicum annuum CaPGIP1 exhibited increased resistance to PGs from Alternaria alternata and Colletotrichum nicotianae[18], and the overexpression of AtPGIPs in A. thaliana enhanced its resistance to B. cinerea infection[15], indicating that the over-expression of PGIP could effectively inhibit the infection by various fungal pathogens. This report suggested that PGIP genes function in systemic resistance of plants to pathogens
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