Involvement of jasmonic acid signalling in bacterial wilt disease resistance induced by biocontrol agent Pythium oligandrum in tomato

Abstract

When the biocontrol agent Pythium oligandrum (PO) colonizes the rhizosphere, it suppresses bacterial wilt disease in tomato ( Solanum lycopersicum cv. Micro-Tom) caused by Ralstonia solanacearum , and a homogenate of its mycelia exhibits elicitor activity, inducing an ethylene (ET)-dependent defence response in Micro-Tom. Since salicylic acid (SA) and jasmonic acid (JA) play an important role in plant defence responses to pathogens, the involvement of SA-and JAdependent signal transduction pathways in resistance to R. solanacearum was investigated in tomato roots treated with a mycelial homogenate of PO. Bacterial wilt disease was also suppressed in tomato cv. Moneymaker treated with the PO homogenate. However, the SA-inducible PR-1 ( P6 ) gene was not up-regulated in either Micro-Tom or Moneymaker. SA did not accumulate in homogenate-treated roots in comparison with distilled water-treated controls, even 24 h after inoculation. Induced resistance against R. solanacearum was not compromised in SA-non-accumulating NahG transgenic plants treated with the PO homogenate. On the other hand, the expression of the JA-responsive gene for the basic PR-6 protein was induced in both tomato cultivars treated with the PO homogenate. Furthermore, quantitative disease assays showed that the induced resistance against R. solanacearum was compromized in PO homogenate-treated jai1-1 mutant plants defective in JA signalling. These results indicated that the JA-dependent signalling pathway is required for PO-induced resistance against R. solanacearum in tomato.

Jasmonate signaling in plant interactions with resistance-inducing beneficial microbes

“…For instance, in tomato the JA-insensitive mutant def1 (defenseless 1) and the ET-insensitive mutant Nr (Never ripe) were not capable of mounting ISR against the oomycete pathogen Phytophthora infestans upon colonization of the roots by the PGPR Bacillus pumilus SE34 or P. fluorescens 89B61 (Yan et al, 2002). Similarly, colonization of the roots of wildtype and nahG-expressing tomato plants by the non-pathogenic oomycete P. oligandrum resulted in a decrease in Ralstonia solanacearum-inflicted disease symptoms, whereas the ISR response was blocked in mutant jai1 (jasmonic acid insensitive 1) plants (Hase et al, 2008). In addition, using nahG-expressing rice, an ET-insensitive OsEIN2 antisense rice line, and the JA-deficient rice mutant hebiba, De Vleesschauwer et al (2008) demonstrated that the ability of P. fluorescens WCS374r to trigger ISR against the rice leaf blast pathogen Magnaporthe oryzae is regulated by an SA-independent but JA/ET-modulated signaling pathway.…”

“…Moreover, transgenic Arabidopsis NahG plants that are unable to accumulate SA due to ectopic expression of the bacterial salicylate hydroxylase gene nahG, showed a similar level of induced disease resistance upon colonization of the roots by WCS417r as did wildtype plants, indicating that WCS417r-ISR functions independently of SA (Pieterse et al, 1996). Since then, many examples of SA-independent ISR have been demonstrated in Arabidopsis (Ahn et al, 2007;Iavicoli et al, 2003;Ryu et al, 2003;Segarra et al, 2009;Stein et al, 2008;Van Wees et al, 1997) and other plant species, such as tobacco (Press et al, 1997;Zhang et al, 2002), cucumber (Press et al, 1997), tomato (Hase et al, 2008;Tran et al, 2007;Yan et al, 2002), and rice (De Vleesschauwer et al, 2008). Hence, the ability to activate an SA-independent pathway controlling systemic disease resistance seems to be common for beneficial microorganisms and occurs in a broad range of plant species against different types of attackers.…”

“…(Vinale et al, 2008), Penicillium sp. GP16-2 (Hossain et al, 2008), Pythium oligandrum (Hase et al, 2008), Piriformospora indica (Waller et al, 2005) and related Sebacinales spp. .…”

Influence of Pythium oligandrum Biocontrol on Fungal and Oomycete Population Dynamics in the Rhizosphere

“…Le Floch and coworkers suggested that mycoparasitism is not the main mode of action (23). Root colonization by P. oligandrum may induce systemic resistance associated with the synthesis of elicitors protecting the plant from its aggressors (4,17,31,37,56). Several studies have investigated formulations of P. oligandrum oospores applied to soil or seeds, and their production and use, to optimize the efficacy of biocontrol (9,30).…”

Rhizobacteria induces resistance against Fusarium wilt of tomato by increasing the activity of defense enzymes

“…The antagonists UFV 252, UFV 592 and UFV 618 effectively reduced the Fusarium wilt severity at the same level of hormone JA. JA and its derivatives have been considered as signaling molecules for inducing systemic resistance, which is effective against pathogens with different lifestyles (Hase et al, 2008). In a study using tomato plants incapable of producing JA (def1), plants inoculated with five of eight pathogens were more susceptible to two bacteria (Pseudomonas syringae and X. campestris), two fungi (Verticillium dahliae and Fol) and an oomycete (Phytophthora infestans) but were not altered in their resistance to Cladosporium fulvum, Oidium neolycopersici and Septoria lycopersici.…”