The origin and evolution of vascular tissue regulators TMO5 and LHW

Abstract

Chapter 1 as the closest living relatives to Embryophytes (Figure 2A). Charophytic algae can be divided in six main lineages: Mesostigmatophyceae, Chlorokybophyceae, Klebsormidiophyceae, Charophyceae, Zygnematophyceae and Coleochaetophyceae (Figure 2A) (Mattox and Stewart, 1984; McCourt et al., 2004). Phylogenetic studies have indicated that Mesostigmatophyceae and Chlorokybophyceae are the earliest diverging lineages within the Charophytes (Figure 2A) (Bhattacharya and Medlin, 1998; Lemieux et al., 2007; Simon et al., 2006). Indeed, morphologically, these are the simplest two Streptophyte algae: Mesostigma (the only genus in the Mesostigmatophyceae) is unicellular containing two flagella and Chlorokybus (the only member of the Chlorokybophyceae) forms packets of a few cells. Filamentous algae are found in the Klebsormidiophyceae lineage (Figure 2C), which diverged after Mesostigmatophyceae and Chlorokybophyceae (Figure 2A). These filamentous algae generally do not contain specialized or differentiated cells and branching is very rare (Mikhailyuk et al., 2014). Instead, branching as well as increased morphological complexity in general, is mostly observed in the three later diverging Charophytes. Charales (the only order in the Charophyceae) for example, are large morphologically complex macroscopic algae with differentiated cells and an apical meristem (Figure 2D). They generally contain a central stalk with many branches (Figure 2D). Furthermore, other innovations are present in the later diverging Charophytes, contributing to complexity. For example, Charales and Coleochaetophyceae develop plasmodesmata, allowing cell-cell communication. While the three early diverging lineages use furrowing during the cytokinesis step of cell division, Zygnematophyceae, Charophyceae and Coleochaetophyceae, produce a phragmoplast, similar to Embryophytes. Zygnematophyceae and Coleochaete are thought to be the closest related to Embryophytes (Figure 2A). However, the Zygnematophyceae lineage appears to have lost many traits such as plasmodesmata, flagella and extensive branching. Lycophytes Pterophytes Pteridophytes (Seedless) Gymnosperms Angiosperms Charophytes Chlorophytes Streptophytes Viridiplantae (The green lineage) Embryophytes (Land plants) Tracheophytes (Vascular) Spermatophytes (Seeds) Bryophytes (Non-vascular) Eudicots Monocots Ferns Horstails Liverworts Hornworts Mosses Figure 1. Overview of the plant taxonomy within the plant kingdom. 12 Chapter 1 The colonization of land by an ancestor related to Charophyte algae, was followed by the emergence of the first land plants, approximately 460 million years ago (Lemieux et al., 2007; Lewis and McCourt, 2004; Wellman et al., 2003). The earliest diverging Embryophytes are mosses, liverworts and hornworts, collectively known as Bryophytes (Figure 1). This lineage holds a key position in evolution, as they diverged after the transition from water to land, but prior to the emergence of vascular tissues. Indeed, Bryophytes are plants without lignified vascular systems or true ...