Me and my favourite plant have some things in common. Yes, thale cress (or Arabidopsis thaliana) is smaller, green, and only lives for approximately eight weeks, but other than that, we share some things.
Just like me, Arabidopsis undergoes several developmental stages throughout its life cycle (Figure 1). It starts out as a cute little baby plant in a seed. After germination, the seedling (toddler plant) produces leaves and builds photosynthetic capabilities. Then, plant puberty hits. The activity of about half the genes of the Arabidopsis genome changes, and with the onset of plant adulthood, it acquires the ability to reproduce. If the environmental conditions are favorable, Arabidopsis stops producing leaves and starts flowering to make new baby plants (seeds). A few weeks later, the adult plant retires. Senescence begins, and the formation of flowers stops. Instead, the dying parent plant transfers nutrients to its offspring, the seeds ripen, and the cycle starts again. Throughout its life cycle, my little green friend carried out different growth programs: First, it germinated, then it developed leaves, followed by flowers, and then it stopped producing new organs altogether.
Plants adapt their growth program according to environmental and internal signals, such as day length and plant age. To achieve this, they must maintain and regulate their ability to develop new organs. They need to keep some cells around that can develop into any cell type. Or, to put it into more scientific words: Plants have to maintain a population of undifferentiated stem cells and regulate their activity. In summary, plants perceive and process signals, then the activity of stem cells changes and later, we see a new leaf, a new flower, or the arrest of organ development.
Stem cells are kept at the center of a specialised structure, the meristem (Figure 2). The shape and size of the meristem are dynamic throughout the different developmental stages (Figure 3). During plant puberty, the number of stem cells increases (3a). During plant retirement, the meristem shrinks again (3b). This indicates that stem cell maintenance and activity might be regulated differently in the distinct growth programs.
As part of my research, I investigate how Arabidopsis coordinates stem cell activity, cell sizes and identities within its meristem, across different developmental stages. I use a specialised type of microscopy (called confocal laser scanning microscopy) of fluorescent reporter lines (Figure 4). If the nucleus of a cell glows pink, a marker gene for stem cells is active (CLAVATA3). If a cell’s nucleus shows yellow fluorescence, a different marker gene is expressed (WUSCHEL). This way, I can identify different cell types within meristems and characterise mutant plants impaired in the regulation of stem cell maintenance. These plants either have more, less, or mislocated pink and yellow cells. The specific mutant, I my research focusses on, lacks a small signalling peptide (CLE40), which has previously been shown to be involved in stem cell maintenance in the Arabidopsis shoot by Schlegel et al. (2021).
Understanding how plants maintain their ability to grow is a crucial aspect of plant science because it is related to the yield per plant. If we learn more about the intricate network of regulators involved in plant development, we can use targeted approaches to modify crops and improve their yield. This can contribute to a more sustainable agriculture in the future.
Under the heading Planter’s Punch we present each month one special aspect of the CEPLAS research programme. All contributions are prepared by our early career researchers.
Svenja Augustin is a PhD student in the group of Rüdiger Simon at the Institute for Developmental Genetics (HHU). The research at this institute focusses on the maintenance of stem cells in different plant species. In 2021, Svenja joined the group to investigate the function of a small signalling molecule, CLE40, in the shoot apical meristem of Arabidopsis thaliana.
Schlegel, J. et al. Control of Arabidopsis shoot stem cell homeostasis by two antagonistic CLE peptide signalling pathways. eLife10, e70934 (2021).
Kinoshita, A. et al. Regulation of shoot meristem shape by photoperiodic signaling and phytohormones during floral induction of Arabidopsis. eLife9, e60661 (2020).
Merelo, P., González-Cuadra, I. & Ferrándiz, C. A cellular analysis of meristem activity at the end of flowering points to cytokinin as a major regulator of proliferative arrest in Arabidopsis. Current Biology0, (2021).