Enhanced Defense Responses in Arabidopsis Induced by the Cell Wall Protein Fractions from Pythium oligandrum Require SGT1, RAR1, NPR1 and JAR1

Abstract

The cell wall protein fraction (CWP) is purified from the non-pathogenic biocontrol agent Pythium oligandrum and is composed of two glycoproteins (POD-1 and POD-2), which are structurally similar to class III elicitins. In tomato plants treated with CWP, jasmonic acid (JA)- and ethylene (ET)-dependent signaling pathways are activated, and resistance to Ralstonia solanaceraum is enhanced. To dissect CWP-induced defense mechanisms, we investigated defense gene expression and resistance to bacterial pathogens in Arabidopsis thaliana ecotype Col-0 treated with CWP. When the leaves of Col-0 were infiltrated with CWP, neither visible necrosis nor salicylic acid (SA)-responsive gene (PR-1 and PR-5) expression was induced. In contrast, JA-responsive gene (PDF1.2 and JR2) expression was up-regulated and the resistance to R. solanaceraum and Pseudomonas syringae pv. tomato DC3000 was enhanced in response to CWP. Such CWP-induced defense responses were completely compromised in CWP-treated coi1-1 and jar1-1 mutants with an impaired JA signaling pathway. The induction of defense-related gene expression after CWP treatment was partially compromised in ET-insensitive ein2-1 mutants, but not in SA signaling mutants or nahG transgenic plants. Global gene expression analysis using cDNA array also suggested that several other JA- and ET-responsive genes, but not SA-responsive genes, were up-regulated in response to CWP. Further analysis of CWP-induced defense responses using another eight mutants with impaired defense signaling pathways indicated that, interestingly, the induction of JA-responsive gene expression and enhanced resistance to two bacterial pathogens in response to CWP were completely compromised in rar1-1, rar1-21, sgt1a-1, sgt1b (edm1) and npr1-1 mutants. Thus, the CWP-induced defense system appears to be regulated by JA-mediated and SGT1-, RAR1- and NPR1-dependent signaling pathways.

Pythium oligandrum: an example of opportunistic success

“…Because induced resistance to Ralstonia solanacearum is not compromised in CWP-treated nahG transgenic tomato mutants (transgenic plants expressing the bacterial salicylate hydroxylase gene) while it is compromised in jai1-1 mutants with an impaired JA signalling pathway (Hase et al, 2008), it is tempting to speculate that, analogous to other beneficial associations (Van der Ent et al, 2009), the JA-dependent signalling pathway is required in the CWP-mediated induced resistance. The recent use of an array of mutants with different impaired defence signalling pathways brought conclusive evidence for an involvement of the JA-and ETdependent signalling pathways in the CWP-induced plant response (Kawamura et al, 2009). It seems likely that the strong activation of the JA signalling pathway by CWPs from P. oligandrum results in the suppression of the SA signalling pathway through hormonal cross-talk mechanisms.…”

Proteomic identification of differentially expressed proteins in Arabidopsis in response to methyl jasmonate

“…Indole acetic acid (IAA) is a growth hormone that has been correlated with JA activity (Kawamura et al, 2009). Local IAA accumulation in the basal meristem of Arabidopsis roots was shown to increase after JA treatment (Sun et al, 2009).…”

“…1). Coronatine-regulated tyrosine aminotransferase (CORI3, spots 146 and 147) has been reported to be induced by JAs and aphid feeding (Myzus persicae and Brevicoryne brassicae) (Kusnierczyk et al, 2007;Kawamura et al, 2009). The up-regulation of these proteins indicates that JAs are potent regulators of the processes involved in abiotic and biotic stress response and tolerance (Desikan et al, 2001;Goulas et al, 2007;Jiang et al, 2007).…”

Implications of oligomeric forms of POD-1 and POD-2 proteins isolated from cell walls of the biocontrol agent Pythium oligandrum in relation to their ability to induce defense reactions in tomato

“…This biocontrol agent quickly and massively colonizes tomato root tissues like Pythium-major pathogens, but its colonization is associated with neither host wall disruption nor host cell alternations and is followed by induction of several host defense reactions (Le Floch et al, 2005). We previously reported that a cell wall protein fraction (CWP) of P. oligandrum containing two novel elicitin-like proteins, POD-1 and POD-2 induced defense reactions in sugar beet (Takenaka et al, 2003), wheat (Takenaka et al, 2003), tomato Kawamura et al, 2009a), and Arabidopsis thaliana (Kawamura et al, 2009b). In tomato leaves treated with CWP, JA-and ET-dependent signaling pathways are activated (Kawamura et al, 2009a).…”