Prof Robert Sablowski
Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, UK
How genes shape plants: coordination between cell growth, cell cycle and tissue patterning during plant growth
We aim to understand how regulatory genes modify tissue growth and consequently plant morphology,focussing on floral organ and stem development in Arabidopsis.
Plant tissue growth is based on oriented cell growth and cell proliferation; although both have been studied in detail, little is known about how these processes are coordinated with each other. We became interested in this question while studying the control of floral organ growth by the zinc finger transcription factor JAGGED (JAG). Quantitative analysis of cell geometry and cell cycle progression suggested that a cell size check point operates in the meristem but is turned off by JAG in organ primordia (1). Experiments using transient perturbation of cell sizes in the meristem revealed that meristem cells assessand correct their size, confirming that cell growth and cell cycle are actively coupled and not simply controlled in parallel. A genome-wide screen for JAG targets revealed that JAG directly represses genes that control the G1-S transition of the cell cycle (KRP2 and KRP4). Mutations in both genes partially suppressed jag defects in organ size and shape,showing that to a large degree JAG shapes plant organs by releasing a constraint on cell cycle progression (2). We also found that KRP4 mediates the effects of JAG on the coordination between cell growth and cell cycle. One of our main interests now is the relevance of this regulated cell size checkpoint for organ development; current data indicate that control of cell size is important for correct patterning of the meristem.
Another link between the control of cell cycle and meristem patterning emerged from our study of how DELLA proteins control stem development. We found that DELLA genes function mostly in the apical region of the inflorescence stem, that these genes control shoot meristem size and that this function is mediated by regulation of KRP2 in the deeper region of the shoot meristem (the rib meristem). Our current hypothesis is that DELLAs affect meristem size through growth of the WUSCHEL-expressing region, which produces signals required for meristem maintenance.
Overall, our work highlights the roles of KRP cell cycle regulators in the coordination between cell growth, cell cycle and tissue patterning in plants.
1.Schiessl et al, Current Biology 22: 1739-1746, 2012.
2.Schiessl et al., PNAS 111: 2830–2835, 2014.