Homology, Homeosis, and Process Morphology in Plants

Sattler, Rolf

doi:10.1016/b978-0-08-057430-1.50019-6

Cited by 40 publications

(53 citation statements)

References 61 publications

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“…This conundrum was addressed by Sattler’s concepts of “partial homology” and “continuum morphology” or “process morphology” (e.g. Sattler, 1990; Sattler, 1992; Sattler, 1994; Sattler & Jeune, 1992, see also Fisher & Rutishauser, 1990), which emphasize the dynamic aspect of plant form – the compound leaf is considered intermediate between a simple leaf and a leafy shoot. Interestingly, there is some genetic basis for these concepts; for example, KNOX genes not only play a role in shoot meristem maintenance and organization but are also implicated in compound leaf development (e.g.…”

Section: Discussionmentioning

confidence: 99%

Organ homologies in orchid flowers re-interpreted using the Musk Orchid as a model

Rudall

Perl

Bateman

2013

PeerJ

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Background and Aims. The presence of novel structures in orchid flowers, including auricles, rostellum and bursicles on the gynostemium and a lobed labellum, has prompted long-standing homology disputes, fuelled by conflicting evidence from a wide range of sources. Re-assessment of this debate using an improved model is timely, following recent phylogenetic insights and on the cusp of a revolution in developmental genetics.Methods. We use new data from floral development and anatomy in the small-flowered terrestrial orchid Herminium monorchis as a model to explore organ homologies in orchid flowers within the context of a review of recent literature on developmental genetics.Key Results. The apex of the median carpel of Herminium is trilobed, and the bursicles develop from its lateral lobes, relatively late in flower ontogeny. The bursicles enclose the viscidia, which adhere to the tapetal remnants to form a caudicle linking the viscidium with the pollinium. The auricles are initiated earlier than the bursicles, but they also remain unvascularized. The deeply trilobed labellum possesses three vascular traces, in contrast with the lateral petals, each of which contains a single vascular trace. The two lateral labellum traces diverge from the traces supplying the two adjacent lateral sepals. Data from flower ontogeny and anatomy conflict with respect to organ homologies.Conclusions. Much progress has recently been made in understanding the exceptional differentiation shown by orchids among perianth segments, focusing on multiple copies of the DEF/AP3 subclass of B-class MADS-box genes. In contrast, untangling homologies of profound congenital union of multiple floral organs forming the orchid gynostemium is hampered by their profound congenital union, which we ascribe to overlap in gene expression between organs. Thus, the functional morphology of the orchid flower could ultimately reflect extreme synorganization and associated genetic integration. Analogizing the deeply lobed orchid labellum with a compound leaf, we speculate that KNOX genes could be implicated not only in their demonstrated role in spur development but also in the development of both the characteristic lobed morphology of the orchid labellum and the lobing of the median carpel that differentiates the bursicles and rostellum.

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Section: Discussionmentioning

confidence: 99%

Organ homologies in orchid flowers re-interpreted using the Musk Orchid as a model

Rudall

Perl

Bateman

2013

PeerJ

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“…Most such transitions can be assigned to one of the two main categories of evolutionary–developmental change: heterochrony, a temporal change in the expression of a trait between putative ancestor and descendant, or heterotopy, a spatial (positional) change in the expression of a trait putative ancestor and descendant (note that other narrower definitions are available: cf. Sattler, 1988, 1994; Zelditch & Fink, 1996). However, the monocot flower usefully challenges the applicability of many of the key assumptions that underlie classical interpretations of heterochrony, not least: (a) the integrity of the supposedly distinct boundary between heterochrony and heterotopy; (b) the most appropriate categorization of the complete suppression of a particular structure; and (c) the significance of fusion of organs (synorganization).…”

Section: Discussion Part 2: Heterochrony Heterotopy and Fusionmentioning

confidence: 99%

Evolution of zygomorphy in monocot flowers: iterative patterns and developmental constraints

2004

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Contents Summary 25 Introduction 28 Background 27 Asparagales 28 Commelinids: ZHC clade 29 Commelinids: Poales 32 Conceptual transitions among floral forms revisited 34 Examples from monocot flowers 37 Specific cases of ontogenetic transitions between contrasting floral morphs 39 Conclusions 40 Acknowledgements 42 References 42 Summary Here we explore morphological transitions among monocot flowers and discuss them in terms of modification of existing structures. Monocot flowers are typically arranged in five whorls (carpels, inner and outer stamens, inner and outer tepals), and are radially symmetrical, constructed around a 3‐fold axis of rotational symmetry that delineates three planes of bilateral symmetry. Differential development of one or two of the three organs within a whorl inevitably emphasizes one plane of symmetry, by eliminating the other planes, rendering the whorl zygomorphic. Zygomorphy (monosymmetry) has evolved more than once in monocotyledons. Stamen suppression is a widespread aspect of zygomorphy and conforms to two broad categories of pattern. In the more frequent Pattern 1, 1–3(−5) adaxial stamens (both inner and outer) are either reduced in size or entirely suppressed. Pattern 2 involves loss, reduction or modification of at least the outer abaxial stamen. Pattern 2 often characterizes groups that are phylogenetically embedded within Pattern 1 clades, perhaps indicating that this pattern results from loss of function or overexpression of the same genes involved in establishment of Pattern 1. Heterotopy has been an important evolutionary phenomenon among Zingiberales (some stamens becoming petaloid) and perhaps grasses (petals possibly becoming sepaloid). Heterochrony is the most frequent cause of more subtle changes in the degree of bilateral symmetry shown by monocot flowers by enhancing (peramorphosis) or retarding (paedomorphosis) individual organs within specific whorls.

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“…If these differences can be hypothesised to the state of a unique transformation series (character) in the course of evolution, the original homology hypothesis is still corroborated (modified criterion of intermediate forms, Remane 1952). As other authors have noted, the third criterion does not establish sameness but rather indicates a continuum or an injunction (Sattler 1994 and references therein), due to the inclusion of a transformation hypothesis. Indication of congruent development : A homology hypothesis concerning a pattern is corroborated by congruence with the spatio‐temporal pattern of its processes of pattern formation and pattern stabilization. No developmental ‘criterion’ was formulated by Remane, but intermediate forms in the course of evolution have been viewed as examples of his ‘third criterion’ (e.g., Zachos & Hoßfeld 2006).…”

Section: Corroboration Of Homology Hypothesesmentioning

confidence: 99%

Section: Corroboration Of Homology Hypothesesmentioning

confidence: 99%

Homology: a synthetic concept of evolutionary robustness of patterns

Szucsich¹,

Wirkner²

2007

Zoologica Scripta

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Homology: a synthetic concept of evolutionary robustness of patterns. -Zoologica Scripta, 36 , 281-289. The history of the homology concept is a history of attempts to conceive the basis of sameness in biology. Since it was formulated in the middle of the 19th century, the concept has had to fit an ever growing number of scientific fields and purposes. These different demands have resulted in diverging, sometimes, incompatible definitions. The inconsistencies are mostly due to the lack of a clear separation of hypotheses of maintenance from hypotheses of transformation.A synthetic approach to define homology thus has to consider the following pivotal points: (i) hypotheses of evolutionary maintenance should be kept separate from hypotheses of evolutionary transformation; (ii) the definition of homology should provide the foundation for exact specifications of what is hypothesised to be homologous and (iii) restrictions to particular levels of observation or specific scientific purposes, and the exclusion of iterative homology should be avoided.We suggest that patterns should be delineated by characterizing components of traits, and by describing connections and interactions between these components. A shared pattern of compared traits where the characterization shows 1 : 1 correspondence may then be homologised. Homology is equivalent to a hypothesis that the pattern, starting from a single starting point, was transmitted robustly along diverging branches of a genealogical tree, that is, the homologised pattern was never changed by any transformation.The proposed definition of homology is thus, ' A pattern corresponding in a set of compared traits is homologous, if after a common evolutionary origin, the pattern was maintained along diverging lineages by robust pattern transmission '.After justifying the terminological use in our definition, we discuss the interplay of our definition with the pivotal points mentioned above in comparison to other definitions.Since our homology definition is a concept of pattern maintenance, it is clearly demarcated from transformation hypotheses, which are covered by the character concept. Robustness is understood as evolutionary maintenance of correspondence in objects linked by genealogical relations. The characterization of the pattern suffices to provide the necessary conditional phrase by specifying what is hypothesised to be homologous. Allowing development to be conceptualised as a pattern formation process makes it easier to deal with traits that are transmitted indirectly to the next generation. Patterns can be characterized on all observational levels, but the components and the quality of connections and interactions used for the characterization may differ. The replacement of the reference to an ancestor-descendant relationship by a reference to robust pattern transmission allows for the inclusion of iterative homology into the concept.In the final part of the paper, detailed reformulations of the 'criteria' for the corroboration of homology hypotheses as proposed by R...

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Homology, Homeosis, and Process Morphology in Plants

Cited by 40 publications

References 61 publications

Organ homologies in orchid flowers re-interpreted using the Musk Orchid as a model

Organ homologies in orchid flowers re-interpreted using the Musk Orchid as a model

Evolution of zygomorphy in monocot flowers: iterative patterns and developmental constraints

Homology: a synthetic concept of evolutionary robustness of patterns

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