Ectopic B-Type Cyclin Expression Induces Mitotic Cycles in Endoreduplicating Arabidopsis Trichomes

Abstract

Cell differentiation is frequently accompanied by a switch from a mitotic division cycle to an endoreduplication cycle. In endoreduplicating cells, DNA synthesis continues in the absence of cell divisions, and it is speculated that endoreduplication represents a shortened mitotic division cycle. In animals, it has been shown that cells switching from mitotic to endoreduplication cycles continue to express factors controlling the G1-S transition, whereas the transcription of mitotic factors controlling the G2-M transition is negatively regulated. It is unknown how the mitotic factors are repressed and what the functional significance of their suppression is. To test the function of two mitotic cyclins in an endoreduplication cycle, we expressed CYCLIN B1;1 and CYCLIN B1;2 in unicellular Arabidopsis trichomes. During wild-type development, trichomes undergo an average of four endoreduplication cycles, leading to a DNA content of approximately 32C. We find that ectopic expression of CYCLIN B1;2, not CYCLIN B1;1, induces mitotic divisions resulting in multicellular trichomes. The CYCLIN B1;2-triggered cell divisions appeared normal with respect to both nuclear division and cytokinesis. We show that CYCLIN B1;2 is misexpressed in the siamese mutant, which also produces multicellular trichomes. Additional overexpression of CYCLIN B1;2 in a siamese mutant background caused a strongly enhanced phenotype.

Ectopic D-type cyclin expression induces not only DNA replication but also cell division in Arabidopsis trichomes

“…4h). Also by expressing CYCB1;2 in trichomes multicellular trichomes arise (13). There, a similar correlation between an increasing number of cells per trichomes and a decreasing amount of DNA can be found.…”

“…Both trichome marker lines pGL1::GUS and pGL2::GUS were a gift from David Marks (10,11), and the pCYCB1;1::GUSDB reporter line, FA4C, was a gift from Peter Doerner (12). The pCYCB1;2::GUSDB reporter line has been described previously (13).…”

“…Ectopic expression of CYCB1;2 but not CYCB1;1 also leads to multicellular trichomes (13). However, expression of the mitotic cyclin results in a much weaker phenotype, with on average only 2-3 cells per multicellular trichome.…”

“…There, a similar correlation between an increasing number of cells per trichomes and a decreasing amount of DNA can be found. Summing up the DNA content of all single nuclei in pGL2::CYCB1;2 trichomes as being the total DNA content per TIS revealed that the wild-type total DNA content of 32C would not be exceeded (13). Therefore, we analyzed the total DNA content per TIS in pGL2::CYCD3;1 plants.…”

The anaphase promoting complex/cyclosome is required during development for modified cell cycles

“…These results are consistent with a role for the APC͞C in the maintenance of the endo cycle in polyploid plant cells, though effects on the onset of the endo cycle were not addressed by these analyses. Elimination of mitotic cyclin protein is necessary for endo cycles in plants, because ectopic expression of cyclin B1;2 in Arabidopsis trichome cells causes these cells to undergo mitosis rather than endo cycles (33).…”