Phylogenetic Analyses and Morphological Innovations in Land Plants

Abstract

An increasingly robust phylogenetic framework based on molecular and fossil data clarifies the sequence of evolutionary innovations in land plants. Oogamy and cellular novelties (phragmoplast, plasmodesmata, incipient meristems) evolved in aquatic streptophytes. Invasion of the land entailed interpolation of the sporophyte, jacketed gametangia and sporangia, and air‐dispersed spores, followed by stomata. Origin of vascular plants involved branching of the sporophyte and stepwise evolution of vascular tissue. Leaves originated independently in lycophytes and euphyllophytes; in some euphyllophytes leaves were derived from single dichotomous branches, in others from whole branch systems. In seed plants, secondary growth evolved before the seed. Pinnately compound leaves were replaced by simple leaves in coniferophytes. The origin of the angiosperm flower remains unresolved, but bitegmic ovules may be derived from cupules, and the ancestral carpel can be reconstructed as ascidiate. Evolution of double fertilization was a stepwise process that continued within angiosperms; vessels also evolved within the group. Monocots show major reorganization tied to loss of secondary growth, while pentamerous flowers evolved from dimerous within eudicots.

PIN proteins and the evolution of plant development

“…Although initial characterization in a heterologous system suggested that PINA was ER localized and PIND cytosolic [7], analysis of these proteins in their native context demonstrates that, consistent with their structures, PINA is plasma membrane localized and PIND is ER localized [27,28]. PINA sometimes shows polar localization, but can be also apolarly localized depending on tissue and developmental stage [28] The plant phylogeny presented here is based on current consensus, and follows that presented in [18]. It should be noted that the phylogeny is not definitive, and some details remain unresolved or controversial; for instance, there is currently uncertainty regarding the relative positions of Charales and Zygnematales (as illustrated here), and regarding the interrelation of the bryophyte groups.…”

“…In this case, PAT could also be a shared-ancestral characteristic of charophytes and land plants, and PIN proteins in the Charales might be rather more similar to canonical PINs than to KfPIN and/or SpPIN ( Figure 1). An alternative view is that the simple algae in the Zygnematales are the sister group to embryophytes [19,20], which would have required them to undergo severe reductions in complexity [18,20]. If Zygnematales are sister to embryophytes, then either most of the canonical PIN structure evolved after their divergence, or SpPIN has also undergone reduction from ancestral proteins that were more canonical in structure (and it is notable that SpPIN is less similar to canonical PINs than is KfPIN).…”

“…Bryophytes: collective name for liverworts, mosses, and hornworts, three ancient plant groups that diverged from vascular plants early in land-plant evolutionary history. It is generally thought that they do not form a monophyletic clade, but rather a paraphyletic grade with respect to vascular plants (e.g., [18]) ( Figure 1, main text); the exact interrelation of these groups to each other remains unclear. However, they have several common features, including a dominant gametophytic phase.…”

“…However, it is not clear whether this PAT is PIN mediated, or even homologous to PAT in land plants. The details of streptophyte phylogeny are still unclear; the classic view is that Charales are sister to land plants, and that aspects of their complex development (e.g., apical cells) are shared-ancestral characteristics ( Figure 1) [18]. In this case, PAT could also be a shared-ancestral characteristic of charophytes and land plants, and PIN proteins in the Charales might be rather more similar to canonical PINs than to KfPIN and/or SpPIN ( Figure 1).…”

“…Diagram illustrating the major morphological innovations in land plant evolution, and the possible contributions of auxin transport to those innovations. Major innovations are described on the gray tree, the nature and order of these follows the scheme presented in[18]; it should be noted that this is not definitive, and other reconstructions are plausible. Distances are not proportional to elapsed evolutionary time.…”