Compound leaf development in model plant species
Introduction
Leaf development follows three continuous and overlapping phases, initiation, primary morphogenesis (PM), also referred to as morphogenesis, and secondary morphogenesis (SM), also referred to as differentiation [1]. During initiation, the leaf emerges from the flanks of the shoot apical meristem (SAM). During morphogenesis, the lamina is initiated and leaf marginal structures such as leaflets, lobes and serrations are formed. During differentiation, the leaf area grows substantially, leaf tissues mature and differentiate, and the final leaf form is determined.
The variability of compound-leaf forms is generated by flexible tuning of partially common players. It is therefore informative to study leaf development in different species. Cardamine (Cardamine hirsuta), pea (Pisum sativum), medicago (Medicago truncatula) and tomato (Solanum lycopersicum) all possess compound leaves. Here, we focus on key factors involved in leaf development in the above mentioned model plants. Leaf development of these plant species is presented in Box 1 and Figure 1. Using tomato leaf development as a context, we will stress the similar and divergent elements in leaf development of each of the model species as they are known today.
Section snippets
Morphogenesis and differentiation in compound leaves
The formation of a compound leaf requires the maintenance of transient morphogenetic activity at the leaf margin, in a region called marginal blastozone (MB) [2]. The extent of this window of morphogenetic activity affects the variability in leaf shape, and is defined by the antagonistic activities of differentiation promoting and differentiation delaying factors. Below we discuss some of these factors and how they function in different compound-leaf species.
Transcription factors from the
Marginal patterning in compound leaves
Marginal patterning involves the formation of serrations, lobes and leaflets at the leaf margin, thus contributing to the variability in leaf form. Formation of marginal structures results from differential growth in adjacent regions [46, 47••]. Simple leaves can have either a smooth leaf margin (such as the maize leaf) or a serrated leaf margin (such as Arabidopsis). Compound leaves show an additional level of marginal patterning, forming separate leaflets that like simple leaves can each be
Concluding remarks
Throughout development, plants utilize similar mechanisms in context specific ways, resulting in numerous variations of plant form. Thus, orthologous ‘tools’ — primarily hormones and transcription factors — are used in different contexts to balance indeterminate and determinate growth, and to specify the location and form of lateral organs. Compound-leaf development has served as an attractive model to study these principles.
By way of an illustrative example, leaf development in Pea seems to have
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
• of special interest
•• of outstanding interest
Acknowledgements
Work on leaf development in the Ori lab is supported by grants from the Israel Science foundation (60/10 and 539/14), U.S.–Israel Binational Agricultural Research and Development Fund (IS 4531-12C) and German-Israel Project Cooperation Foundation (OR309/1-1; FE552/12-1). Maya Bar is partially funded by the Lady Davis Fellowship Trust. We thank Rujin Chen, Julie Hofer and Miltos Tsiantis for providing the images of medicago, caradmine and pea respectively, and members of the Ori group for
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