Drawing a Line: Grasses and Boundaries

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.

CmBES1 is a regulator of boundary formation in chrysanthemum ray florets

“…Boundary formation is critical to the function of mature organs because it allows for correct patterning and separation of different activities. These boundaries are regulated by complex networks that include transcription factors and the spatial distribution of growth-promoting hormones such as auxin and BRs 1,6 . In Arabidopsis, the core gene involved in BR signaling and the node of multiple signal cascades is BZR1, which is closely related to organ fusion.…”

“…Organogenesis is the process of tissue production by multipotent progenitor cells and is common to all multicellular organisms 1 . Lateral organs such as leaves and flowers are formed by lateral organ primordia, where cells are recruited from the periphery of the meristem 2 .…”

“…Organ boundaries are regulated by complex networks comprising transcription factors and miRNAs and the spatial distribution of growth-promoting hormones such as auxin and brassinosteroids (BRs) 1 , 6 . The key genes involved in boundary regulation include CUP-SHAPED COTYLEDON 1/2/3 ( CUC ), LATERAL ORGAN FUSION ( LOF ), GROWTH REGULATING FACTOR ( GRF ), and LATERAL ORGAN BOUNDARY ( LOB ), and the corresponding mutants of these genes have organ fusion phenotypes that contribute to our understanding of the importance of their roles in boundary regulation 7 – 10 .…”

Plant Development and Organogenesis: From Basic Principles to Applied Research

“…Richardson and Hake [3] consider another fascinating aspect of organogenesis at the shoot apical meristem, the formation of boundaries between pluripotent meristematic cells and differentiating organs. Their review critically summarizes the current understanding of boundary specification during vegetative development in grass crops in comparison with eudicot models.…”

“…When we called for this Special Issue we were not prepared to such a prompt and enthusiastic response from the many friends/colleagues working in basic or applied research. We received many excellent manuscripts that made a major effort in forecasting translational solutions to improve crop production while addressing and reviewing fundamental knowledge of key plant developmental processes in model species [2,3,4,5,6]. Important contributions also came from researchers working on crop species [7,8] and plant breeding companies [6,9] that decided to openly share their strategies with the scientific community.…”