Abstract
Delineation between distinct populations of cells is essential for organ development. Boundary formation is necessary for the maintenance of pluripotent meristematic cells in the shoot apical meristem (SAM) and differentiation of developing organs. Boundaries form between the meristem and organs, as well as between organs and within organs. Much of the research into the boundary gene regulatory network (GRN) has been carried out in the eudicot model Arabidopsis thaliana. This work has identified a dynamic network of hormone and gene interactions. Comparisons with other eudicot models, like tomato and pea, have shown key conserved nodes in the GRN and species-specific alterations, including the recruitment of the boundary GRN in leaf margin development. How boundaries are defined in monocots, and in particular the grass family which contains many of the world’s staple food crops, is not clear. In this study, we review knowledge of the grass boundary GRN during vegetative development. We particularly focus on the development of a grass-specific within-organ boundary, the ligule, which directly impacts leaf architecture. We also consider how genome engineering and the use of natural diversity could be leveraged to influence key agronomic traits relative to leaf and plant architecture in the future, which is guided by knowledge of boundary GRNs.
Highlights
Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA; USDA Plant Gene Expression Center, 800 Buchanan Street, Albany, CA 94710, USA
We focus on the development of a grass-specific within-organ boundary, the ligule, which directly impacts leaf architecture
The formation of PIN-FORMED 1 (PIN1) convergence points in the shoot apical meristem (SAM) of the model eudicot plant Arabidopsis thaliana is essential for organ initiation [11,12,13,14,15]
Summary
Organogenesis is the self-organizing process in which complex tissues arise from pluripotent progenitors and is common to all multicellular organisms. Phyllotaxy is determined by the distribution of the phytohormone auxin, which is influenced by the directional export of auxin by the PIN-FORMED transporters (PIN) This process is a self-organizing feedback loop, and the spacing between each primordium is predicted to be influenced by the size of the region of auxin depletion around the older primordium [4,5,6,7,8,9,10]. The formation of PIN1 convergence points in the SAM of the model eudicot plant Arabidopsis thaliana is essential for organ initiation [11,12,13,14,15] This PIN1 convergence point leads to the formation of an auxin maximum and the subsequent downregulation of KNOX genes, which allows differentiation and outgrowth of organ primordia
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