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Summary: Amphicarpy is an unusual trait where two fruit types develop on the same plant: one above and the other belowground. This trait is not found in conventional model species. Therefore, its development and molecular genetics remain under‐studied. Here, we establish the allooctoploid Cardamine chenopodiifolia as an emerging experimental system to study amphicarpy.We characterized C. chenopodiifolia development, focusing on differences in morphology and cell wall histochemistry between above‐ and belowground fruit. We generated a reference transcriptome with PacBio full‐length transcript sequencing and analysed differential gene expression between above‐ and belowground fruit valves.Cardamine chenopodiifolia has two contrasting modes of seed dispersal. The main shoot fails to bolt and initiates floral primordia that grow underground where they self‐pollinate and set seed. By contrast, axillary shoots bolt and develop exploding seed pods aboveground. Morphological differences between aerial explosive fruit and subterranean nonexplosive fruit were reflected in a large number of differentially regulated genes involved in photosynthesis, secondary cell wall formation and defence responses.Tools established in C. chenopodiifolia, such as a reference transcriptome, draft genome assembly and stable plant transformation, pave the way to study amphicarpy and trait evolution via allopolyploidy. [ABSTRACT FROM AUTHOR]

Finding causal relationships between genotypic and phenotypic variation is a key focus of evolutionary biology, human genetics and plant breeding. To identify genome-wide patterns underlying trait diversity, we assembled a high-quality reference genome of Cardamine hirsuta, a close relative of the model plant Arabidopsis thaliana. We combined comparative genome and transcriptome analyses with the experimental tools available in C. hirsuta to investigate gene function and phenotypic diversification. Our findings highlight the prevalent role of transcription factors and tandem gene duplications in morphological evolution. We identified a specific role for the transcriptional regulators PLETHORA5/7 in shaping leaf diversity and link tandem gene duplication with differential gene expression in the explosive seed pod of C. hirsuta. Our work highlights the value of comparative approaches in genetically tractable species to understand the genetic basis for evolutionary change.

Emonet and Hay describe how plants actively disperse seeds using exploding fruit. [ABSTRACT FROM AUTHOR]

Author(s): Stephen P. Grigg [1]; Claudia Canales [1]; Angela Hay [1]; Miltos Tsiantis (corresponding author) [1] Leaves of flowering plants are determinate organs produced by pluripotent structures termed shoot apical [...]

Recent development in KNOTTED1-like HOMEOBOX (KNOX) pathway functions, the interconnections between KNOX genes and hormones and the way in which they regulate shoot development are reviewed. However, it remains to be seen whether other development genes act as regulators of the hormone activities or is it a KNOX gene specific function.

Background and Aims Seeds are dispersed by explosive coiling of the fruit valves in Cardamine hirsuta. This rapid coiling launches the small seeds on ballistic trajectories to spread over a 2 m radius around the parent plant. The seed surface interacts with both the coiling fruit valve during launch and subsequently with the air during flight. We aim to identify features of the seed surface that may contribute to these interactions by characterizing seed coat differentiation. Methods Differentiation of the outermost seed coat layers from the outer integuments of the ovule involves dramatic cellular changes that we characterize in detail at the light and electron microscopical level including immunofluorescence and immunogold labelling. Key Results We found that the two outer integument (oi) layers of the seed coat contributed differently to the topography of the seed surface in the explosively dispersed seeds of C. hirsuta vs. the related species Arabidopsis thaliana where seed dispersal is non-explosive. The surface of A. thaliana seeds is shaped by the columella and the anticlinal cell walls of the epidermal oi2 layer. In contrast, the surface of C. hirsuta seeds is shaped by a network of prominent ridges formed by the anticlinal walls of asymmetrically thickened cells of the sub-epidermal oi1 layer, especially at the seed margin. Both the oi2 and oi1 cell layers in C. hirsuta seeds are characterized by specialized, pectin-rich cell walls that are deposited asymmetrically in the cell. Conclusions The two outermost seed coat layers in C. hirsuta have distinct properties: the sub-epidermal oi1 layer determines the topography of the seed surface, while the epidermal oi2 layer accumulates mucilage. These properties are influenced by polar deposition of distinct pectin polysaccharides in the cell wall. Although the ridged seed surface formed by oi1 cell walls is associated with ballistic dispersal in C. hirsuta , it is not restricted to explosively dispersed seeds in the Brassicaceae. [ABSTRACT FROM AUTHOR]