Genetic architecture of a pollinator shift and its fate in secondary hybrid zones of two Petunia species.

Background: Theory suggests that the genetic architecture of traits under divergent natural selection influences how easily reproductive barriers evolve and are maintained between species. Divergently selected traits with a simple genetic architecture (few loci with major phenotypic effects) should facilitate the establishment and maintenance of reproductive isolation between species that are still connected by some gene flow. While empirical support for this idea appears to be mixed, most studies test the influence of trait architectures on reproductive isolation only indirectly.

Single gene mutation in a plant MYB transcription factor causes a major shift in pollinator preference.

Understanding the molecular basis of reproductive isolation and speciation is a key goal of evolutionary genetics. In the South American genus Petunia, the R2R3-MYB transcription factor MYB-FL regulates the biosynthesis of UV-absorbing flavonol pigments, a major determinant of pollinator preference. MYB-FL is highly expressed in the hawkmoth-pollinated P.

Complex evolution of novel red floral color in Petunia.

Red flower color has arisen multiple times and is generally associated with hummingbird pollination. The majority of evolutionary transitions to red color proceeded from purple lineages and tend to be genetically simple, almost always involving a few loss-of-function mutations of major phenotypic effect. Here we report on the complex evolution of a novel red floral color in the hummingbird-pollinated Petunia exserta (Solanaceae) from a colorless ancestor.

Gain and Loss of Floral Scent Production through Changes in Structural Genes during Pollinator-Mediated Speciation.

The interactions of plants with their pollinators are thought to be a driving force in the evolution of angiosperms. Adaptation to a new pollinator involves coordinated changes in multiple floral traits controlled by multiple genes. Surprisingly, such complex genetic shifts have happened numerous times during evolution.

Tight genetic linkage of prezygotic barrier loci creates a multifunctional speciation island in Petunia.

Most flowering plants depend on animal vectors for pollination and seed dispersal. Differential pollinator preferences lead to premating isolation and thus reduced gene flow between interbreeding plant populations. Sets of floral traits, adapted to attract specific pollinator guilds, are called pollination syndromes.

Mechanical regulation of auxin-mediated growth.

Background: The phytohormone auxin is a primary regulator of growth and developmental pattern formation in plants. Auxin accumulates at specific sites (e.g.

Pin1-independent leaf initiation in Arabidopsis.

Phyllotaxis, the regular arrangement of leaves and flowers around the stem, is a key feature of plant architecture. Current models propose that the spatiotemporal regulation of organ initiation is controlled by a positive feedback loop between the plant hormone auxin and its efflux carrier PIN-FORMED1 (PIN1). Consequently, pin1 mutants give rise to naked inflorescence stalks with few or no flowers, indicating that PIN1 plays a crucial role in organ initiation.

Stem cell activation by light guides plant organogenesis.

Leaves originate from stem cells located at the shoot apical meristem. The meristem is shielded from the environment by older leaves, and leaf initiation is considered to be an autonomous process that does not depend on environmental cues. Here we show that light acts as a morphogenic signal that controls leaf initiation and stabilizes leaf positioning.

Integration of transport-based models for phyllotaxis and midvein formation.

The plant hormone auxin mediates developmental patterning by a mechanism that is based on active transport. In the shoot apical meristem, auxin gradients are thought to be set up through a feedback loop between auxin and the activity and polar localization of its transporter, the PIN1 protein. Two distinct molecular mechanisms for the subcellular polarization of PIN1 have been proposed.

Auxin influx carriers stabilize phyllotactic patterning.

One of the most striking features of plant architecture is the regular arrangement of leaves and flowers around the stem, known as phyllotaxis. Peaks in concentration of the plant hormone auxin, generated by the polar localization of the PIN1 auxin efflux carrier, provide the instructive signal for primordium initiation. This mechanism generates the spacing between neighboring primordia, which results in regular phyllotaxis.

Single gene-mediated shift in pollinator attraction in Petunia.

Animal-mediated pollination is essential in plant reproductive biology and is often associated with pollination syndromes, sets of floral traits, such as color, scent, shape, or nectar content. Selection by pollinators is often considered a key factor in floral evolution and plant speciation. Our aim is the identification and characterization of the genetic changes that caused the evolution of divergent pollination syndromes in closely related plant species.

A plausible model of phyllotaxis.

A striking phenomenon unique to the kingdom of plants is the regular arrangement of lateral organs around a central axis, known as phyllotaxis. Recent molecular-genetic experiments indicate that active transport of the plant hormone auxin is the key process regulating phyllotaxis. A conceptual model based on these experiments, introduced by Reinhardt et al.

Pyruvate decarboxylase provides growing pollen tubes with a competitive advantage in petunia.

Rapid pollen tube growth places unique demands on energy production and biosynthetic capacity. The aim of this work is to understand how primary metabolism meets the demands of such rapid growth. Aerobically grown pollen produce ethanol in large quantities.

Microsurgical and laser ablation analysis of leaf positioning and dorsoventral patterning in tomato.

Leaves are arranged according to regular patterns, a phenomenon referred to as phyllotaxis. Important determinants of phyllotaxis are the divergence angle between successive leaves, and the size of the leaves relative to the shoot axis. Young leaf primordia are thought to provide positional information to the meristem, thereby influencing the positioning of new primordia and hence the divergence angle.

Domains of expansin gene expression define growth regions in the shoot apex of tomato.

Expansins are members of a multigene family of extracellular proteins, which increase cell wall extensibility in vitro and thus are thought to be involved in cell expansion. The major significance of the presence of this large gene family may be that distinctly expressed genes can independently regulate cell expansion in place and time. Here we report on LeExp9, a new expansin gene from tomato, and compare its expression in the shoot tip with that of LeExp2 and LeExp18.

Regulation of phyllotaxis by polar auxin transport.

The regular arrangement of leaves around a plant's stem, called phyllotaxis, has for centuries attracted the attention of philosophers, mathematicians and natural scientists; however, to date, studies of phyllotaxis have been largely theoretical. Leaves and flowers are formed from the shoot apical meristem, triggered by the plant hormone auxin. Auxin is transported through plant tissues by specific cellular influx and efflux carrier proteins.

Microsurgical and laser ablation analysis of interactions between the zones and layers of the tomato shoot apical meristem.

Plants exhibit life-long organogenic and histogenic activity in a specialised organ, the shoot apical meristem. Leaves and flowers are formed within the ring-shaped peripheral zone, which surrounds the central zone, the site of the stem cells. We have undertaken a series of high-precision laser ablation and microsurgical tissue removal experiments to test the functions of different parts of the tomato meristem, and to reveal their interactions.