Mitotic B-type cyclins are differentially regulated by phytohormones and during yellow lupine nodule development

The progression of cell cycle in eukaryotes is controlled by protein complexes composed of p34 protein kinase and cyclin subunits. Recently, we have described four B1 type mitotic cyclin in yellow lupine. The presence of several closely related cyclin genes within the same plant species raised the question about tissue specificity of respective cyclins or their different regulations by plant-specific signals. Therefore, we examined the expression pattern of four B1 cyclins in various lupine tissues, with special emphasis put on developing root nodules. We also studied the effect of phytohormones on the level of respective cyclin mRNAs. As expected, cyclin transcript accumulation was restricted to proliferating tissues. Detailed analysis by reverse transcription-PCR and using primers specific to each cyclin allow to establish that different genes are engaged in cell divisions of various meristematic tissues. All four genes were activated during nodule development, however, the Cyc3 and Cyc4 genes mostly at the early stages of nodulation, whereas the Cyc1 and Cyc2 genes within the mature nodule organs. The expression of cyclins was regulated differently by plant growth factors. Both auxin and cytokinin induced the Cyc1 and Cyc4 genes and their transcript level was also abundant within the root, shoot and floral meristems. The precise localisation of cyclin transcripts by in situ hybridisation revealed that lupine nodule meristem was active during the whole process of nodule development, even in old organs. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.