Eight types of stem cells in the life cycle of the moss Physcomitrella patens

Abstract

Physcomitrella patens develops at least seven types of simplex meristem in the gametophyte and at least one type in the sporophyte generation and is a good material for regulatory network comparisons. In this review, we summarize recently revealed molecular mechanisms of stem cell initiation and maintenance in the moss. Kofuji and Hasebe 3 Diversity of stem cells in land plantsStem cells have the ability to self-renew and to form differentiated cells, and several types of stem cells are formed during development and growth [1,2]. Since stem cells are the sources of body parts, their appropriate regulation is necessary in order to generate the body plan successfully. The morphological and anatomical organization of stem cells varies among land plants [3] (Table 1), and comparisons of their regulatory systems in different land plant lineages should be useful in deducing the evolution of body plans as well as understanding the commonalities and differences in stem cell regulatory systems. After several days of cultivation, chloronema apical stem cells transform into caulonema apical stem cells that produce caulonema cells [12]. Both chloronemata and caulonemata are filamentous, and together they are referred to as protonemata.Chloronema cells with round, green chloroplasts are adaptive for photosynthesis, whereas caulonema cells, which are characterized by more rapid growth and spindle-shaped, less-green chloroplasts, are adapted for expansion. The transition from a chloronema to a caulonema apical stem cell is enhanced and retarded by glucose and ammonium ion, respectively, supplemented in the medium, suggesting that the stem cell transition is regulated by the carbon/nitrogen ratio [13] via photosynthesis and metabolic genes including hexokinase [14,15]. Phytochrome and cryptochrome signaling pathways inhibit the chloronema-to-caulonema transition [16,17]. Auxin [18] and the basic helix-loop helix transcription factors ROOT HAIR DEFECTIVE SIX-LIKE1 (PpRSL1) and PpRSL2 [19] as well as diterpenes derived from a gibberellin precursor [20] positively regulate the transition, whereas cytokinin is a indispensable factor for shoot stem cell initiation and maintenance in angiosperms [48] with regulation at the upper levels [49,50]. However, loss of class 1 KNOX genes in Physcomitrella does not cause defects in sporophyte stem cell division other than slight changes in the division angle, but instead causes pleiotropic defects in the later stages of development, suggesting that meristem functions of class 1 KNOX genes were acquired Kofuji and Hasebe 8 in the angiosperm lineage after the divergence of the moss lineage [51].After the PRC2-mediated arrest of sporophyte apical stem cell activity, the cells that have already been produced divide to form the three major parts of a sporophyte body: a sporangium that forms spores via meiosis, a seta that serves as a stalk for the sporangium, and a foot that anchors the sporophyte and interacts with the gametophore tissue [39,51]. The seta meristem has higher cell division...

Insights into the Evolution of Hydroxyproline-Rich Glycoproteins from 1000 Plant Transcriptomes

“…The information revealed by MAAB in the 1KP data detailing the suite of AGPs present in bryophytes in addition to the increasing use of the bryophyte models P. patens (Kofuji and Hasebe, 2014) and Marchantia polymorpha (Ishizaki et al, 2016) will facilitate molecular approaches to investigate the functions of specific AGPs through, for example, mutant studies.…”

Can mosses serve as model organisms for forest research?

“…1c), possess a three-faced apical meristematic cell which supports the formation of leafy shoots (Aoyama et al 2012;Harrison et al 2009). The role and response of hormones during the different developmental stages and possible culture conditions are well characterized and reviewed elsewhere (Bonhomme et al 2013;Decker et al 2006;Kofuji and Hasebe 2014;Strotbek et al 2013). For research, moss tissue can easily be cultivated either on agar plates where gametophores are formed within few weeks or as protonema in liquid medium.…”

WOX13-like genes are required for reprogramming of leaf and protoplast cells into stem cells in the moss Physcomitrella patens

“…The absence of WUS-clade WOX genes in mosses raises the question of how stem cells are regulated. In contrast to the complex meristems of seed plants, growth of mosses depends on single, apical stem cells that undergo asymmetric cell divisions (Kofuji and Hasebe, 2014). In the gametophytic phase of Physcomitrella, chloronema and caulonema stem cells form filaments (Prigge and Bezanilla, 2010) and the gametophore stem cell gives rise to a leafy shoot (Harrison et al, 2009).…”