Unravelling 3D growth in the moss Physcomitrium patens

Abstract

The colonization of land by plants, and the greening of the terrestrial biosphere, was one of the most important events in the history of life on Earth. The transition of plants from water to land was accompanied, and largely facilitated, by the acquisition of apical cells with three or more cutting faces (3D growth). This enabled plants to develop the morphological characteristics required to survive and reproduce effectively on land and to colonize progressively drier habitats. Most plants develop in such a way that makes genetic studies of 3D growth difficult as the onset of 3D growth is established early during embryo development. On the other hand, in the moss Physcomitrium patens, the onset of 3D growth is preceded by a protracted 2D filamentous phase of the life cycle that can be continuously propagated. P. patens is an ideal model system in which to identify the genetic toolkit underpinning the 2D to 3D growth transition, and this is because 3D growth is not a pre-requisite for survival. Thus, insights into the mechanisms underpinning the formation of apical cells and the subsequent establishment and maintenance of 3D growth have largely been gained through studies in P. patens. This review summarizes the most recently published articles that have provided new and important insights into the mechanisms underpinning 3D growth in P. patens.

The Shoot Apical Meristem: An Evolutionary Molding of Higher Plants

“…(b) Schematic representation of streptophyte phylogeny based on AM anatomy through gametophyte and sporophyte life stages. Within the charophycean algae, the apical meristem is a single cell with one cutting face [51,53]. Within bryophytes, a variety of apical meristems are found, including unicellular meristems with one, two, three, and four cutting sides, as well as simple multicellular meristems consisting of two cells with eight cutting sides [50,54].…”

“…The dome-shaped apical cells of Charales have one cutting face opposite the apex of the surface, and this cutting plane is parallel to the orientation of the last cell plate. As a result, they present 1D growth, forming cell chains resembling filaments or mats [51,53]. Another charophyte, the Coleochaetalean algae, typically exhibits a marginal meristem where cells can divide into two possible planes, leading to the formation of radially symmetrical filamentous or monochromatic thalli that resemble hornwort gametophytes [66].…”

“…Both substages comprise a protonema apical cell. Lastly, moss initiates 3D growth and leafy shoot buds called gametophores with a single tetrahedral apical cell [53]. In contrast, hornworts and liverworts do not possess a protonemal stage; after spore germination, they grow directly into thalli or "leafy" forms [54,76].…”

Cytokinins specify pluripotent stem cell identity in the mossPhyscomitrium patens

“…The root apical meristem is the originator of all of the cells in the root system (5). The advent of stem cells that can produce distinct cell types has been the driving force behind the remarkable morphological diversity of plants, which enabled the colonization of terrestrial environments and the success of land plants (6)(7)(8)(9). In flowering plants (angiosperms), a group of stem cells is maintained at the center of the SAM, while the SAM of bryophytes and most ferns contain a single stem cell known as the apical cell (Fig.…”

A special issue of Essays in Biochemistry on evolutionary developmental biology

“…When plants conquered land, they evolved the ability to grow in three dimensions, which enabled the diversification of plant form. The review by Moody discusses what the moss Physcomitrium patens can tell us about the genetic toolkit that enabled this transition [13].…”