Plant hormones: a key in clubroot development.

Clubroot disease causes gall formation on Brassica roots. A holistic approach was undertaken to understand the role of plant hormones in early clubroot symptom development in Arabidopsis. We used the CYCB1;1::GUS, DR5::GUS and ARR5::GUS constructs to assess clubroot initiation. We compared plant hormone concentration between control and infected plants, screened different hormone mutants for resistance and evaluated auxin transport. Also, a differential proteome study was performed using two dimensional gel electrophoresis coupled to MALDI-TOF. Combining the hormone and proteome data, we postulate that at the first stages of clubroot disease, cytokinins are produced by the pathogen. This triggers a local re-initiation of cell division in the root cortex. Consequently, a de novo meristematic area is established that acts as a sink for host-derived IAA, carbohydrates, nitrogen and energy to maintain the pathogen and to trigger gall development.