Accumulation of defense related transcripts in sunflower hypocotyls (Helianthus annuus L.) infected with Plasmopara halstedii

A cDNA clone encoding a sunflower chitinase was obtained using degenerated primers in PCR amplifications and RACE procedures. This clone, a phenylalanine ammonia-lyase (PAL) clone and ubiquitin clone were used to analyse the resistance of sunflower (Helianthus annuus) to downy mildew. The differential regulation of amounts of PAL (involved in the general pathway of phenylpropanoid synthesis), chitinase (a pathogenesis-related protein) and ubiquitin (involved in proteolytic pathways) mRNA was studied in hypocotyls during the early stages after an aerial infection of sunflower inbred line RHA274 with zoospores from either race 1 (incompatible, host resistant) or race B (compatible, host susceptible) of Plasmopara halstedii. Northern analyses showed that transcript levels of PAL, chitinase and ubiquitin were rapidly and strongly increased after infection in incompatible interactions but not in the compatible ones, suggesting that regulation of these mRNAs is an important component of the resistance mechanisms in sunflower.