<i>SlWRKY45</i>, nematode-responsive tomato <i>WRKY</i> gene, enhances susceptibility to the root knot nematode; <i>M. javanica</i> infection

The fluctuation of tomato's WRKY defense regulators during infection by the root knot nematode <i>Meloidogyne javanica</i> was analyzed: and the spatial and temporal expression of <i>SlWRKY45</i> was studied in depth with regard to its response to nematode infection, phytohormones, and wounding. Expression of <i>WRKY45</i> increased substantially within 5 d upon infection and continued through feeding-site development and gall maturation. Histological analysis of nematode feeding sites indicated that <i>WRKY45</i> was highly expressed within the feeding cells and associated vascular parenchyma cells. Responses of SlWRKY45 promoters to several phytohormones showed that <i>WRKY45</i> was highly induced by specific phytohormones, including cytokinin, auxin, and the defense-signaling molecule salicylic acid (SA), but not by the jasmonates. Overexpressing tomato lines were generated, and infection tests showed that, significantly, roots over-expressing SlWRKY45 contained substantially increased number of females, indicating that <i>WRKY45</i> overexpression supported faster nematode development. qRT-PCR tests have shown roots overexpressing <i>WRKY45</i> suppressed the jasmonic acid and salicylic acid marker genes, proteinase inhibitor (PI), and pathogenesis related protein (PR1), respectively, and also the cytokinin response factors <i>CRF1</i> and <i>CRF6</i>. Overall, this study indicated SlWRKY45 to be a potential transcription factor whose manipulation by the invading nematode might be critical for coordination of hormone signals supporting favorable condition for nematode development in root tissue<i>.</i>