Abstract
Kunitz-type (PKPI) and Potato type I (Pin1) protease inhibitors (PIs) are two families of serine proteinase inhibitors often associated to plant storage organs and with well known insecticidal and nematicidal activities. Noteworthy, their ability to limit fungal and bacterial pathogenesis in vivo or to influence plant physiology has not been investigated in detail. To this aim, we generated a set of PVX-based viral constructs to transiently and heterologously express two potato PKPI (PKI1, PKI2) and three potato Pin1 (PPI3A2, PPI3B2, PPI2C4) genes in Nicotiana benthamiana plants, a widely used model for plant-pathogen interaction studies. Interestingly, transgenic plants expressing most of the tested PIs showed to be highly resistant against two economically important necrotrophic fungal pathogens, Botrytis cinerea and Alternaria alternata. Unexpectedly, overexpression of the PKI2 Kunitz-type or of the PPI2C4 and PPI3A2 Potato type I inhibitor genes also lead to a dramatic reduction in the propagation and symptom development produced by the bacterial pathogen Pseudomonas syringae. We further found that localized expression of PPI2C4 and PKI2 in N. benthamiana leaves caused an increase in cell expansion and proliferation which lead to tissue hypertrophy and trichome accumulation. In line with this, the systemic expression of these proteins resulted in plants with enhanced shoot and root biomass. Collectively, our results indicate that PKPI and Pin1 PIs might represent valuable tools to simultaneously increase plant fitness and broad-spectrum resistance toward phytopathogens.
Highlights
PKPI and Pin1 are among the most abundant naturally occurring plant serine proteinase inhibitors (PIs)
Inhibitors of these enzymes, especially those belonging to the multigene PI families PKPI and Pin1 have been shown to accumulate in plant tissues in a highly precise spatial and temporal manner and following both abiotic and biotic threats (Hermosa et al, 2006; Wang et al, 2008; Singh et al, 2009; Turrà et al, 2009; Boex-Fontvieille et al, 2015; Rustgi et al, 2017)
From the complex set of plant-produced PIs, different protein products belonging to the PKPI and Pin1 serine proteinase inhibitor families and showing high inhibitory activity on both fungal growth and disease development when exogenously supplemented to the fungal inoculum source (Hermosa et al, 2006)
Summary
PKPI and Pin are among the most abundant naturally occurring plant serine proteinase inhibitors (PIs). Large amounts of these inhibitors accumulate in plant reproductive and storage organs, as in the case of Solanum tuberosum (Heibges et al, 2003; van den Broek et al, 2004). Their genes are transcribed, at lower levels, in all other plant tissues (Kuo et al, 1984; Lincoln et al, 1987; Jofuku and Goldberg, 1989; Heitz et al, 1993; Wang et al, 2003, 2008; Turrà et al, 2009). While serine PIs insecticidal and nematicidal activities have been efficiently proven in planta, their ability to alter plant resistance against fungal or bacterial pathogens in vivo has remained elusive
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