EST Sequencing of Meloidogyne javanica Infected Pineapple Root Tissues Reveals Changes in Gene Expression during Root-Knot Nematode Induced Gall Formation

An expressed sequence tag project has been performed to survey a range of expressed sequences in the vascular cylinder tissue of pineapple roots infected with the root-knot nematode Meloidogyne javanica. A total of 4,102 EST sequences were obtained, comprising of 1,298 early infection clones, 2,461 late infection clones and 343 non-infected root tip clones. Clone redundancy was 34.4 %, with the 4,102 EST sequences clustering into 2,976 contigs comprising of 286 clusters and 2,690 singletons. A comparison of the most abundant clones isolated from the early and late infection libraries revealed significant differences in the transcriptomes of the vascular cylinder at early and late infection stages. Northern analysis and quantitative real time PCR confirmed a variety of genes including a metallothinein-like protein, an alpha tubulin, a phosphoglyceratemutase, a glyceradehyde phosphate dehydrogenase, a mannose-binding lectin and four previously undiscovered sequences are differentially expressed during gall formation. Analysis of clone distribution by functional classification revealed that the late infection library contains a higher proportion of clones associated with oxidative stress responses and the detoxification of free radicals. The EST and contig sequence collection, bioinformatic data and functional classification information is available through an online pineapple database resource housed at http://genet.imb.uq.edu.au/Pineapple/index.html.