An Integrative Analysis of Fruit Shape in Capsella rubella and Arabidopsis thaliana

Plant organs develop from a small number of cells into a wide variety of shapes. This development is coordinated by underlying genetic factors that control the organisation and patterning of growth. The Arabidopsis fruit has been studied in detail and genes involved in fruit shape development and organisation have been uncovered. Related species that have divergent fruit forms have not been studied in the same detail and it remains unclear if the mechanisms and genes controlling growth organisation and patterning in fruit are common. Here, I give a general description of fruit shape changes within a time framework for Capsella rubella, which has an elaborate heart-shaped fruit. I used clonal analysis to generate a description of regional growth dynamics within the tissue. Using this data, I generated computational models to explore the coordination of growth and polarity in the Capsella fruit. Based on observations of morphology, growth dynamics and model outputs, Capsella fruit development can be divided into three phases. It is likely that there is a proximodistal polarity field that deforms locally as the fruit grows. Changes in growth rates and orientations parallel and perpendicular to this polarity field during the different phases can account for the morphology and clonal patterns of the Capsella fruit. In addition, I investigated factors important for the development of the heart-shaped fruit of Capsella through forward and reverse genetic approaches. I found FRUITFULL is an important factor for the development of the heart-shape fruit of Capsella but may not be important for the evolutionary differences in fruit shape within the family Simplified versions of the Capsella fruit model accounted for fruit shapes of related species including Arabidopsis. This indicates that the Capsella fruit is a more elaborate form of the evolutionary conserved mechanisms that underlie fruit development in the Brassicaceae

Fruit shape diversity in the Brassicaceae is generated by varying patterns of anisotropy

Fruits exhibit a vast array of different 3D shapes, from simple spheres and cylinders to more complex curved forms; however, the mechanism by which growth is oriented and coordinated to generate this diversity of forms is unclear. Here, we compare the growth patterns and orientations for two very different fruit shapes in the Brassicaceae: the heart-shaped Capsella rubella silicle and the near-cylindrical Arabidopsis thaliana silique. We show, through a combination of clonal and morphological analyses, that the different shapes involve different patterns of anisotropic growth during three phases. These experimental data can be accounted for by a tissue-level model in which specified growth rates vary in space and time and are oriented by a proximodistal polarity field. The resulting tissue conflicts lead to deformation of the tissue as it grows. The model allows us to identify tissue-specific and temporally specific activities required to obtain the individual shapes. One such activity may be provided by the valve-identity gene FRUITFULL, which we show through comparative mutant analysis to modulate fruit shape during post-fertilisation growth of both species. Simple modulations of the model presented here can also broadly account for the variety of shapes in other Brassicaceae species, thus providing a simplified framework for fruit development and shape diversity

Shop stewards’ leadership, left-wing activism and collective workplace union organisation

Providing an account of the dynamic interrelationship between shop steward leadership and membership interaction, Ralph Darlington focuses particular attention on the much-neglected crucial role that left-wing political activists can play in shaping the nature of collective workplace relations

HEARTBREAK Controls Post-translational Modification of INDEHISCENT to Regulate Fruit Morphology in Capsella

Morphological variation is the basis of natural diversity and adaptation. For example, angiosperms (flowering plants) evolved during the Cretaceous period more than 100 mya and quickly colonized terrestrial habitats [1]. A major reason for their astonishing success was the formation of fruits, which exist in a myriad of different shapes and sizes [2]. Evolution of organ shape is fueled by variation in expression patterns of regulatory genes causing changes in anisotropic cell expansion and division patterns [3, 4, 5]. However, the molecular mechanisms that alter the polarity of growth to generate novel shapes are largely unknown. The heart-shaped fruits produced by members of the Capsella genus comprise an anatomical novelty, making it particularly well suited for studies on morphological diversification [6, 7, 8]. Here, we show that post-translational modification of regulatory proteins provides a critical step in organ-shape formation. Our data reveal that the SUMO protease, HEARTBREAK (HTB), from Capsella rubella controls the activity of the key regulator of fruit development, INDEHISCENT (CrIND in C. rubella), via de-SUMOylation. This post-translational modification initiates a transduction pathway required to ensure precisely localized auxin biosynthesis, thereby facilitating anisotropic cell expansion to ultimately form the heart-shaped Capsella fruit. Therefore, although variation in the expression of key regulatory genes is known to be a primary driver in morphological evolution, our work demonstrates how other processes—such as post-translational modification of one such regulator—affects organ morphology

Protest logics and the mediation opportunity structure

This article aims to bridge a gap between social movement studies and media and communication studies. A conceptual framework is presented that integrates the political opportunity structure approach and the logics of contentious action with the concept of mediation. The author argues that mediation opportunity structure is a fruitful concept to encompass a wide variety of ways in which media and communication are relevant to protest and social movements. It refers to mainstream media representations of protest and movements, to movements ‘becoming the media’ and counter-spinning, as well as to media and communication practices that constitute protest and resistance in their own right. The manifold articulations of mediation illustrate that media and communication are not merely relevant to the symbolic and discursive realms in which social movements operate, but that they are also instrumental and material to realizing their immediate goals. Activists are becoming more aware and conscious of the mediation opportunity structure, through their lay-knowledge of how the mainstream media and technologies operate, partially adapting to them or appropriating them. The nature and degree of mediation opportunities for activists and the structural constraints impeding the opportunities varies according to the type of protest logic that is being used