  The cambium is a meristematic tissue in plant stems. Here, cell divisions
occur that are required for radial growth of plant stems. Daughters of cell
divisions within the cambium differentiate into woody xylem cells towards the
inside of the stem, or phloem towards the outside. As such, a pattern of
xylem-cambium-phloem is present along the radial axis of the stem. A
ligand-receptor pair, TDIF-PXY promotes cell division in the cambium, as do the
phytohormones, cytokinin and auxin. An auxin response factor, MP, has been
proposed to initiate cambial cell divisions by promoting PXY expression,
however, MP has also been reported to repress cambial cell divisions later in
development where TDIF-PXY complexes are also reported to suppress MP activity.
Here, we used a mathematical modelling approach to investigate how MP cell
division-promoting activity and cell division-repressing activity might be
integrated into the same network as a negative feedback loop. In our model,
this feedback loop improved the ability of the cambium to pattern correctly and
was found to be required for normal patterning when MP was stable. The
implications of this model in early and late cambium development are discussed.
