Abstract
Mosses are an ancient land plant lineage and are therefore important in studying the evolution of plant developmental processes. Here, we describe stomatal development in the model moss species Physcomitrium patens (previously known as Physcomitrella patens) over the duration of sporophyte development. We dissect the molecular mechanisms guiding cell division and fate and highlight how stomatal function might vary under different environmental conditions. In contrast to the asymmetric entry divisions described in Arabidopsis thaliana, moss protodermal cells can enter the stomatal lineage directly by expanding into an oval shaped guard mother cell (GMC). We observed that when two early stage P. patens GMCs form adjacently, a spacing division can occur, leading to separation of the GMCs by an intervening epidermal spacer cell. We investigated whether orthologs of Arabidopsis stomatal development regulators are required for this spacing division. Our results indicated that bHLH transcription factors PpSMF1 and PpSCRM1 are required for GMC formation. Moreover, the ligand and receptor components PpEPF1 and PpTMM are also required for orientating cell divisions and preventing single or clustered early GMCs from developing adjacent to one another. The identification of GMC spacing divisions in P. patens raises the possibility that the ability to space stomatal lineage cells could have evolved before mosses diverged from the ancestral lineage. This would have enabled plants to integrate stomatal development with sporophyte growth and could underpin the adoption of multiple bHLH transcription factors and EPF ligands to more precisely control stomatal patterning in later diverging plant lineages. We also observed that when P. patens sporophyte capsules mature in wet conditions, stomata are typically plugged whereas under drier conditions this is not the case; instead, mucilage drying leads to hollow sub-stomatal cavities. This appears to aid capsule drying and provides further evidence for early land plant stomata contributing to capsule rupture and spore release.
Highlights
Stomata are microscopic pores typically consisting of a pair of guard cells which regulate a central aperture to control gas exchange for photosynthesis and water loss
Building Increasingly Robust Stomatal Developmental Modules In Arabidopsis, as in most other land plants, stomata are spaced by at least one intervening epidermal pavement cell (Hara et al, 2007; Rudall et al, 2013; Caine et al, 2016). This is achieved through orientated amplifying and spacing divisions of stomatal precursors, so that stomatal lineage cells are typically bordered by stomatal lineage ground cell (SLGC) or epidermal pavement cells (Geisler et al, 1998, 2000; Zhao and Sack, 1999; Figures 9A–C)
EPF2 negatively regulates SPCH-SCRM/2 activity in the early stages of the stomatal lineage; EPF1 negatively regulates MUTE-SCRM/2 as meristemoids transition to guard mother cell (GMC); and TOO MANY MOUTHS (TMM) is required for EPIDERMAL PATTERNING FACTOR (EPF) signal transduction (Hara et al, 2007; Hunt and Gray, 2009; Qi et al, 2017)
Summary
Stomata are microscopic pores typically consisting of a pair of guard cells which regulate a central aperture to control gas exchange for photosynthesis and water loss. They are present on the majority of land plants and evolved prior to 418 million years ago (Edwards et al, 1998; Ligrone et al, 2012; Chater et al, 2013, 2017). Vascular land plant stomata regulate plant gaseous exchange, water status, temperature, internal solute transport and can prevent or allow pathogen entry (Yoo et al, 2010; Franks et al, 2015; Hepworth et al, 2015; Dutton et al, 2019). For a more specialized overview of P. patens sporophyte development, see Hiss et al (2017)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
