PvLOX2 silencing in common bean roots impairs arbuscular mycorrhiza-induced resistance without affecting symbiosis establishment

Abstract

The arbuscular mycorrhizal (AM) symbiosis is an intimate association between specific soil-borne fungi and the roots of most land plants. AM colonisation elicits an enhanced defence resistance against pathogens, known as mycorrhizal-induced resistance (MIR). This mechanism locally and systemically sensitises plant tissues to boost their basal defence response. Although a role for oxylipins in MIR has been proposed, it has not yet been experimentally confirmed. In this study, when the common bean (Phaseolus vulgaris L.) lipoxygenase PvLOX2 was silenced in roots of composite plants, leaves of silenced plants lost their capacity to exhibit MIR against the foliar pathogen Sclerotinia sclerotiorum, even though they were colonised normally. PvLOX6, a LOX gene family member, is involved in JA biosynthesis in the common bean. Downregulation of PvLOX2 and PvLOX6 in leaves of PvLOX2 root-silenced plants coincides with the loss of MIR, suggesting that these genes could be involved in the onset and spreading of the mycorrhiza-induced defence response.

Arbuscular Mycorrhizal Symbiosis-Induced Expression Changes in Solanum lycopersicum Leaves Revealed by RNA-seq Analysis

“…In addition to helping to establish mycorrhizal symbiosis and MIR, several oxylipins (including jasmonic acid and some of its derivatives) participate during the onset of priming, which occurs before the manifestation of this resistance (Campos-Soriano et al 2012;Hao et al 2012;Mora-Romero et al 2015). Our results are consistent with these reports, since several genes related to the jasmonate biosynthetic and signaling pathways were differentially expressed in leaves of mycorrhizal tomato plants.…”

“…Furthermore, previous results from our group indicate a role for the oxylipin pathway in common bean leaves during a priming state induced by mycorrhizal symbiosis (Mora-Romero et al 2015).…”

“…and characterization of many genes that are important for this interaction. Examples of these roles include the following: establishing the symbiosis in the root (Harrison 2012), nutrient acquisition from the soil to the fungus and then to the root (Govindarajulu et al 2005;Javot et al 2007), and an increased resistance to root and foliar pathogens, as well as abiotic stresses (Campos-Soriano et al 2012;Kapoor et al 2013;Mora-Romero et al 2015). In line with the occurrence of mycorrhizal colonization in roots, the differential expression of genes in roots of mycorrhizal vs. non-mycorrhizal plants (as observed by microarray analysis) has been reported for Medicago truncatula (Liu et al 2007), Lotus japonicus (Guether et al 2009), tomato (Solanum lycopersicum) (Fiorilli et al 2009), and rice (Oryza sativa) (Güimil et al 2005).…”

“…Several systemic effects on shoots have also been reported in response to mycorrhizal colonization of roots, including an increase in resistance to shoot pathogens and abiotic stresses (Campos-Soriano et al 2012;Mora-Romero et al 2015;Ouziad et al 2006;Pozo et al 2010). Interestingly, far fewer studies have reported the differential expression of genes in shoots of mycorrhizal plants.…”

Metabolic transition in mycorrhizal tomato roots

“…In some plant systems LOX-silencing does not significantly affect AMF colonization, therefore it has been proposed that activation of JA-signaling is a downstream event triggered by this symbiosis ( Wasternack and Hause, 2013 ). In fact, Pv LOX2- silencing in common bean roots is reported to have no effect on mycorrhiza establishment, whilst it does impair mycorrhiza-induced resistance ( Mora-Romero et al, 2014 ). Thus, the results suggest that AM functioning implies a precise regulation of the oxylipin pathway that may contribute to improving stress resistance in mycorrhizal plants.…”