A framework for radial growth via cambial meristem activity

In seed plants, wood provides both the mechanical strength that enables plants to grow tall and a means to transport water to the canopy. Wood is derived from cell divisions in a meristem referred to as the cambium. Although most obvious in forest trees, the cambium is largely conserved in seed plants, including in small rapid-cycling annuals such as Arabidopsis. Arabidopsis is a powerful model organism in which to study cambial regulation due to its rapid-cycling and the vast genetic resources available. Remarkably, the stem cell factors that underpin cambium function were unknown, but we have recently shown that members of the PLT and ANT family of transcription factors represent these elusive stem cell factors1. Our experiments demonstrated the expression of PLT and ANT family members are regulated by a plasma membrane localised receptor kinase, PXY, and its cognate ligand TDIF. However, TDIF-PXY has a suite of additional target transcription factors that perform other roles in cambium maintenance including regulating cell division (WOX4, WOX14)2,3, contributing to patterning (TMO6, LBD4)4 and repressing xylem differentiation (BES1)5. It is not known how the newly identified PLT and ANT stem cell factors integrate into this broader system, but understanding this is a prerequisite to understanding cambium function. The knowledge gap is addressed within this proposal. Given the complexity of the system, to understand how the newly identified factors integrate into the previously known cambium regulatory network requires transformative technologies, in the form of mathematical modelling, to be coupled with genetic approaches. Previous mathematical models of cambial development have captured elements of pattern but not growth1,6 or have incorporated growth but been unable to capture pattern without including hypothetical factors and discarding an important driver of cambium cell division, WOX47. The model proposed here will bridge this modelling gap. We have discovered a new set of transcription factors, members of the PLINC family, that our preliminary unpublished data suggests repress the expression of some TDIF-PXY regulated genes. We hypothesise that a mathematical model that incorporates growth without hypothetical factors and includes WOX4 and members of the PLT and ANT families will pattern correctly upon incorporation of these PLINC transcription factors. Biological data will be used to parameterise the model and model outputs will be tested in planta. Our proposal is focused on generating new fundamental knowledge aimed at understanding the rules of life. Nevertheless, we have previously demonstrated that TDIF-PXY signalling is conserved in forest trees so the discoveries made here will form the basis of future applications. Understanding cambium function is critical because wood represents a globally significant carbon sink and a source of renewable biomaterials. As such the research programme described here could contribute to tackling strategic challenges around renewable resources and clean growth in future.