Expression profiling reveals functionally redundant multiple‐copy genes related to zinc, iron and cadmium responses in B rassica rapa

Summary Genes underlying environmental adaptability tend to be over‐retained in polyploid plant species. Z inc deficiency ( Z n D ) and iron deficiency ( F e D ), excess Z n ( Z n E ) and cadmium exposure ( C d E ) are major environmental problems for crop cultivation, but little is known about the differential expression of duplicated genes upon these stress conditions. Applying T ag‐ S eq technology to leaves of B rassica rapa grown under F e D , Z n D , Z n E or C d E conditions, with normal conditions as a control, we examined global gene expression changes and compared the expression patterns of multiple paralogs. We identified 812, 543, 331 and 447 differentially expressed genes under F e D , Z n D , Z n E and C d E conditions, respectively, in B . rapa leaves. Genes involved in regulatory networks centered on the transcription factors b HLH 038 or b HLH 100 were differentially expressed under ( Z n E ‐induced) F e D . Further analysis revealed that genes associated with Z n, F e and C d responses tended to be over‐retained in the B . rapa genome. Most of these multiple‐copy genes showed the same direction of expression change under stress conditions. We conclude that the duplicated genes involved in trace element responses in B . rapa are functionally redundant, making the regulatory network more complex in B . rapa than in Arabidopsis thaliana .