A Role in Immunity for Arabidopsis Cysteine Protease RD21, the Ortholog of the Tomato Immune Protease C14

Abstract

Secreted papain-like Cys proteases are important players in plant immunity. We previously reported that the C14 protease of tomato is targeted by cystatin-like EPIC proteins that are secreted by the oomycete pathogen Phytophthora infestans (Pinf) during infection. C14 has been under diversifying selection in wild potato species coevolving with Pinf and reduced C14 levels result in enhanced susceptibility for Pinf. Here, we investigated the role C14-EPIC-like interactions in the natural pathosystem of Arabidopsis with the oomycete pathogen Hyaloperonospora arabidopsidis (Hpa). In contrast to the Pinf-solanaceae pathosystem, the C14 orthologous protease of Arabidopsis, RD21, does not evolve under diversifying selection in Arabidopsis, and rd21 null mutants do not show phenotypes upon compatible and incompatible Hpa interactions, despite the evident lack of a major leaf protease. Hpa isolates express highly conserved EPIC-like proteins during infections, but it is unknown if these HpaEPICs can inhibit RD21 and one of these HpaEPICs even lacks the canonical cystatin motifs. The rd21 mutants are unaffected in compatible and incompatible interactions with Pseudomonas syringae pv. tomato, but are significantly more susceptible for the necrotrophic fungal pathogen Botrytis cinerea, demonstrating that RD21 provides immunity to a necrotrophic pathogen.

Serpin1 and WSCP differentially regulate the activity of the cysteine protease RD21 during plant development in Arabidopsis thaliana

“…Binding of RD21 to AtSerpin1, however, is a mechanism to control RD21's activity as prodeath factor (13,14). Changes in vacuole permeability and protease compartmentalization are supposed to account for this set-point control mechanism (8,14). In support of this model, mutant plants lacking RD21 or overexpressing AtSerpin1 both were found to exhibit significantly less elicitor-stimulated programmed cell death than plants lacking AtSerpin1 (8,13,14).…”

“…RD21 was originally discovered as a drought-induced gene in A. thaliana (7). Later studies suggested a role in plant immunity and resistance against necrotrophic fungal pathogens such as Botrytis cinerea (8). RD21 has an interesting structure and biosynthetic pathway.…”

“…Cleavage of the RCL results in an irreversible, covalent serpin::protease adduct (19)(20)(21). Similarly, Arabidopsis Serpin1 forms RD21::Serpin1 adduct (henceforth referred to as RD21-Serpin1) in response to fungal pathogens and was suggested to provide some set-point control of RD21 activity during programmed cell death (8,11,13,14).…”

Enhancement of Rice Resistance to Bacterial Blight by Overexpressing BrCP3 Gene of Brassica rapa

“…Further alignment analysis of their conserved domains showed that both are 83.93% similar in prodomain, 89.25% in protease domain, and 96.49% in granulin domain (data not shown). RD21A is highly overexpressed in the leaf of Arabidopsis particularly during senescence indicating its role in cell death (Shindo et al 2012). Similarly, BrCP3 gene is also remarkably overexpressed in the leaf tissues, about 25-fold higher than in roots and stems of Brassica rapa although the highest levels, 2.48-and 1.39-fold higher than the leaves, were observed respectively in sepal and stamen (Fig.…”

“…Reports have been made on papain-like cysteine proteases acting as inhibitory agent against fungus, bacteria, oomycete and nematode such as Rcr3 (Krüger et al 2002), PIP1 (Tian et al 2007), RD19 (Bernoux et al 2008), RD21 (Shindo et al 2012), C14 (Kaschani et al 2010) and Cath B (Gilroy et al 2007). Each has unique participation in the induction of host immunity which is evident in the specific interactions with the effectors, involvement in a specific molecular battlefield, and the resulting immunity threshold (Niño et al 2014).…”