The Ve-mediated resistance response of the tomato to Verticillium dahliae involves H2O2, peroxidase and lignins and drives PALgene expression

Abstract

BackgroundVerticillium dahliae is a fungal pathogen that infects a wide range of hosts. The only known genes for resistance to Verticillium in the Solanaceae are found in the tomato (Solanum lycopersicum) Ve locus, formed by two linked genes, Ve1 and Ve2. To characterize the resistance response mediated by the tomato Ve gene, we inoculated two nearly isogenic tomato lines, LA3030 (ve/ve) and LA3038 (Ve/Ve), with V. dahliae.ResultsWe found induction of H2O2 production in roots of inoculated plants, followed by an increase in peroxidase activity only in roots of inoculated resistant plants. Phenylalanine-ammonia lyase (PAL) activity was also increased in resistant roots 2 hours after inoculation, while induction of PAL activity in susceptible roots was not seen until 48 hours after inoculation. Phenylpropanoid metabolism was also affected, with increases in ferulic acid, p-coumaric acid, vanillin and p-hydroxybenzaldehyde contents in resistant roots after inoculation. Six tomato PAL cDNA sequences (PAL1 - PAL6) were found in the SolGenes tomato EST database. RT-PCR analysis showed that these genes were expressed in all organs of the plant, albeit at different levels. Real-time RT-PCR indicated distinct patterns of expression of the different PAL genes in V. dahliae-inoculated roots. Phylogenetic analysis of 48 partial PAL cDNAs corresponding to 19 plant species grouped angiosperm PAL sequences into four clusters, suggesting functional differences among the six tomato genes, with PAL2 and PAL6 presumably involved in lignification, and the remaining PAL genes implicated in other biological processes.An increase in the synthesis of lignins was found 16 and 28 days after inoculation in both lines; this increase was greater and faster to develop in the resistant line. In both resistant and susceptible inoculated plants, an increase in the ratio of guaiacyl/syringyl units was detected 16 days after inoculation, resulting from the lowered amount of syringyl units in the lignins of inoculated plants.ConclusionsThe interaction between the tomato and V. dahliae triggered a number of short- and long-term defensive mechanisms. Differences were found between compatible and incompatible interactions, including onset of H2O2 production and activities of peroxidase and PAL, and phenylpropanoid metabolism and synthesis of lignins.

Cationic peroxidase related to basal resistance of Betula platyphylla var. japonica plantlet No.^|^#8201;8 against canker-rot fungus Inonotus obliquus strain IO-U1

“…Moreover, POD was activated more rapidly than phenolic compound accumulation in all the treated plantlets (Figures 1 to 3). These results were in agreement with the previous reports that PODs are involved in polymerization of phenolics, and synthesis of phenolic compounds in relation to plant defense responses against infection and wounding (Bruce and West 1989;Deborah et al 2001;Egea et al 2001;Gayoso et al 2010;Lagrimini 1991;Morkunas and Gmerek 2007). However, B. platyphylla var.…”

The PAL2 promoter activities in relation to structural development and adaptation in Arabidopsis thaliana

“…The PAL2 promoter, which was induced in the root after 2 dpi in the leaves, demonstrated a progressive increase of activity during the pathogen challenge which correlates an induced defence response. During this type of defence response, the production of lignin precursors for strengthening the secondary cell wall (Conrath et al 2002;Hückelhoven 2007;Gayoso et al 2010) was induced, supporting the idea that the activation and the gradual increase of the PAL2 promoter in the root was associated with the plant adaptation to infection which may involve the structural adaptation of the organ. The importance of structural development and adaptation in plants was previously demonstrated in a study using the Arabidopsis pal1 pal2 double mutant where lower deposition of lignin in this plant caused the plants to be more susceptible to infection (Rohde et al 2004;Huang et al 2010).…”

Reactive oxygen species and plant resistance to fungal pathogens

“…Similarly, the generation of H 2 O 2 was detected in cotton roots after infection with Verticillium dahliae ). In a study investigating H 2 O 2 generation upon V. dahliae infection, H 2 O 2 production in tomato plants carrying the Ve resistance gene preceded that observed in a susceptible variety (Gayoso et al, 2010). Transgenic cotton plants expressing a fungal endochitinase gene are more resistant towards Rhizoctonia solani and accumulated ROS faster than the wild type after inoculation with the pathogen (Kumar et al, 2009).…”