Precise control of plant stem cell activity through parallel regulatory inputs
Bennett, T. ; Toorn, A. van; Willemsen, V. ; Scheres, B. - \ 2014
Development 141 (2014). - ISSN 0950-1991 - p. 4055 - 4064.
arabidopsis-thaliana root - transcription factor - shoot apex - meristem - gene - differentiation - organization - maintenance - homeostasis - sombrero
The regulation of columella stem cell activity in the Arabidopsis root cap by a nearby organizing centre, the quiescent centre, has been a key example of the stem cell niche paradigm in plants. Here, we investigate interactions between transcription factors that have been shown to regulate columella stem cells using a simple quantification method for stem cell activity in the root cap. Genetic and expression analyses reveal that the RETINOBLASTOMA-RELATED protein, the FEZ and SOMBRERO NAC-domain transcription factors, the ARF10 and ARF16 auxin response factors and the quiescent centre-expressed WOX5 homeodomain protein each provide independent inputs to regulate the number of columella stem cells. Given the tight control of columella development, we found that these inputs act in a surprisingly parallel manner. Nevertheless, important points of interaction exist; for example, we demonstrate the repression of SMB activity by non-autonomous action of WOX5. Our results suggest that the developmental progression of columella stem cells may be quantitatively regulated by several more broadly acting transcription factors rather than by a single intrinsic stem cell factor, which raises questions about the special nature of the stem cell state in plants.
Impact of light on leaf initiation: a matter of photosynthate availability in the apical bud?
Savvides, A. ; Ntagkas, N. ; Ieperen, W. van; Dieleman, J.A. ; Marcelis, L.F.M. - \ 2014
Functional Plant Biology 41 (2014)5. - ISSN 1445-4408 - p. 547 - 556.
arabidopsis-thaliana - thermal-time - shade-avoidance - air-temperature - young tomato - blue-light - shoot apex - growth - expansion - responses
Radiation substantially affects leaf initiation rate (LIR), a key variable for plant growth, by influencing the heat budget and therefore the temperature of the shoot apical meristem. The photosynthetically active component of solar radiation (photosynthetic photon flux density; PPFD) is critical for plant growth and when at shade to moderate levels may also influence LIR via limited photosynthate availability. Cucumber and tomato plants were subjected to different PPFDs (2.5–13.2 mol m–2 day–1) and then LIR, carbohydrate content and diel net CO2 uptake of the apical bud were quantified. LIR showed saturating response to increasing PPFD in both species. In this PPFD range, LIR was reduced by 20% in cucumber and by 40% in tomato plants. Carbohydrate content and dark respiration were substantially reduced at low PPFD. LIR may be considered as an adaptive trait of plants to low light levels, which is likely to be determined by the local photosynthate availability. In tomato and cucumber plants, LIR can be markedly reduced at low PPFD in plant production systems at high latitudes, suggesting that models solely based on thermal time may not precisely predict LIR at low PPFD.