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 comple xes composed of p34 protein kinase and cyclin subunits. Recently, we have d escribed four B1 type mitotic cyclin in yellow lupine. The presence of seve ral closely related cyclin genes within the same plant species raised the q uestion about tissue specificity of respective cyclins or their different r egulations by plant-specific signals. Therefore, we examined the expression pattern of four B1 cyclins in various lupine tissues, with special emphasi s put on developing root nodules. We also studied the effect of phytohormon es 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 t o establish that different genes are engaged in cell divisions of various m eristematic tissues. All four genes were activated during nodule developmen t, however, the Cyc3 and Cyc4 genes mostly at the early stages of nodulatio n, whereas the Cyc1 and Cyc2 genes within the mature nodule organs. The exp ression of cyclins was regulated differently by plant growth factors. Both auxin and cytokinin induced the Cyc1 and Cyc4 genes and their transcript le vel was also abundant within the root, shoot and floral meristems. The prec ise localisation of cyclin transcripts by in situ hybridisation revealed th at lupine nodule meristem was active during the whole process of nodule dev elopment, even in old organs. (C) 2000 Elsevier Science Ireland Ltd. All ri ghts reserved.