Isolation of differentially expressed genes involved in clubroot disease

The interaction between Plasmodiophora brassicae and its host Brassica rapa is investigated by two strategies. (1) IAA-conjugate hydrolases: Root hypertrophy in club root disease is dependent on increased auxin levels and these could result from auxin-conjugate hydrolysis. So far we isolated 5 different cDNA fragments out of various tissues which revealed high identity to IAR3/ILL5, ILL2, ILL3, ILL6 and ILR1 genes from Arabidopsis by comparison with database entries. (2) Random priming: Using this method, we have so far obtained 26 clones from clubroot tissue, from which several sequences may be components of plant signal transduction chains, metabolic pathways and transcriptional regulation.

Compensatory Mutations in Predicted Metal Transporters Modulate Auxin Conjugate Responsiveness in Arabidopsis

Levels of the phytohormone indole-3-acetic acid (IAA) can be altered by the formation and hydrolysis of IAA conjugates. The isolation and characterization of Arabidopsis thaliana mutants with reduced IAA-conjugate sensitivity and wild-type IAA responses is advancing the understanding of auxin homeostasis by uncovering the factors needed for conjugate metabolism. For example, the discovery that the IAA-Ala-resistant mutant iar1 is defective in a protein in the ZIP family of metal transporters uncovered a link between metal homeostasis and IAA-conjugate sensitivity. To uncover additional factors impacting auxin conjugate metabolism, we conducted a genetic modifier screen and isolated extragenic mutations that restored IAA-amino acid conjugate sensitivity to the iar1 mutant. One of these suppressor mutants is defective in a putative cation diffusion facilitator, MTP5 (At3g12100; formerly known as MTPc2). Loss of MTP5 function restored IAA conjugate sensitivity to iar1 but not to mutants defective in IAA-amino acid conjugate amidohydrolases. Our results are consistent with a model in which MTP5 and IAR1 transport metals in an antagonistic fashion to regulate metal homeostasis within the subcellular compartment in which the IAA-conjugate amidohydrolases reside, and support previous suggestions that the ion composition in this compartment influences hydrolase activity.