Stomata facilitate gas exchange between the plant and its environment. In Arabidopsis thaliana, asymmetric division of the committed protodermal cell produces a stem cell-like cell, meristemoid (in red). A meristemoid can go through asymmetric divisions before forming a guard mother cell (in orange), which divides symmetrically and differentiates into a pair of guard cells (in green). Three closely related and conserved genes encoding basic helix-loop-helix (bHLH) transcription factors SPEECHLESS, MUTE, and FAMA control core stomatal development. SPCH initiates the stomatal lineage by driving asymmetric divisions, MUTE promotes guard mother cell fate and limits asymmetric divisions, and FAMA promotes stable guard cell identity. SPCH can promote three different asymmetric cell division types, (entry, amplifying, and spacing divisions, Figure 1B), which together contribute to the epidermal cell type composition of the leaf (Figure 1A-B).
Our work has shown that cytokinin signaling is one of the regulatory pathways fine-tuning stomatal numbers (Vatén et al., 2018). SPCH and negative regulator of CK signalling, ARR16 (Figure 1C), form a feedback loop, which fine-tunes spacing division likelihood and leads to controlled stomatal numbers.
Figure 1. A) Leaf epidermis consists of stomata and other epidermal cell types, such as lobed pavement cells. B) Stomatal lineage is initiated by asymmetric entry division which produces small meristemoid (in red) and larger SLGC (stomatal lineage ground cell). Meristemoid can go through additional asymmetric amplifying divisions. Also SLGCs can go through asymmetric divisions called spacing divisions. C) SPCH (in yellow) and ARR16 (in cyan) regulate meristemoid divisions (Vatén et al., 2018).
Stomatal development is known to be sensitive to changes in environment; this can be seen both in the fossil record and in present plants as a response of stomatal density, for example, to changing atmospheric carbon dioxide [CO2]. This suggest that environmental conditions can be sensed by the signaling pathways which regulate behaviour of meristemoids (in red). We investigate how stomatal developmental plasticity is regulated at the molecular level and further, how leaf development is coordinated upon changing environmental conditions in Arabidopsis. We are especially interested how information from different signalling pathways is integrated to achieve appropriate epidermal cell type composition. We use both reverse and forward genetic approaches to dissect this broad topic.
Figure 2. Schematic image showing how epidermal divisions contribute to cell type composition of the leaf epidermis. Environmental information is integrated to stomatal developmental program and thus, changes in growth conditions can lead to alterations in stomatal numbers.
We study stomatal development in gymnosperms by using Norway spruce (Picea abies) as a model species.
Our aim is to address three key questions:
(1) how is Norway spruce stomatal development regulated at the molecular level?
(2) how stomatal regulators have diverged after the angiosperm-gymnosperm split?
(3) are the molecular mechanisms controlling stomatal developmental plasticity shared between all seed plants?
Our long-term goal is to pioneer studies on the genetic basis of plant-environment interaction by using stomatal lineage as a model system. Our aim is to understand how plant growth and development is affected by changing climate with a special focus on boreal forest trees.