Red light-induced systemic disease resistance against root-knot nematode Meloidogyne javanica and Pseudomonas syringae pv. tomato DC 3000

The pretreatment of Arabidopsis with red light (600-700 nm) induces systemic resistance against root-knot nematode Meloidogyne javanica and Pseudomonas syringae pv. tomato DC 3000. Red light treatment significantly (P = 0.05) reduced the number of root galls in both wild type (Col-0) and nahG-expressing Arabidopsis compared with those of white light-treated control plants, while red light treatment only induced resistance to P. syringae in wild-type plants. This result suggests that red light induces resistance against root-knot nematode in Arabidopsis through a transduction pathway, which is independent of salicylic acid (SA) accumulation in roots, but resistance to P. syringae is SA-dependent. PR1 gene expression was monitored as a marker for systemic acquired resistance (SAR). Relative quantification of expression of the PR1 gene corresponding to the cDNA was examined in both leaves and roots. There was no significant difference between leaves and roots of red light-treated Arabidopsis in quantitative PR1 gene expression. In red light-treated wild type (Col-0) Arabidopsis, PR1 mRNA was induced by 23.11- and 22.47-fold for leaf and root, respectively, compared with the plants treated with white light. However, in nahG plants, PR1 gene expression changed only by 0.4-fold. These findings indicate that plant defense responses activated by the foliar SA-dependent pathway depend on the specific host-pathogen system. This is the first report of red light-induced resistance in Arabidopsis against root-knot nematode.