Abstract
SummaryThe origin of the stem is a major but poorly understood aspect of plant development, partly because the stem initiates in a relatively inaccessible region of the shoot apical meristem called the rib zone (RZ). We developed quantitative 3D image analysis and clonal analysis tools, which revealed that the Arabidopsis homeodomain protein REPLUMLESS (RPL) establishes distinct patterns of oriented cell division and growth in the central and peripheral regions of the RZ. A genome-wide screen for target genes connected RPL directly to many of the key shoot development pathways, including the development of organ boundaries; accordingly, mutation of the organ boundary gene LIGHT-SENSITIVE HYPOCOTYL 4 restored RZ function and stem growth in the rpl mutant. Our work opens the way to study a developmental process of importance to crop improvement and highlights how apparently simple changes in 3D organ growth can reflect more complex internal changes in oriented cell activities.
Highlights
All plant growth is sustained by stem cell populations located within the apical meristems (Aichinger et al, 2012)
The underlying rib zone (RZ) gives rise to the stem and includes a central region called the rib meristem, which gives rise to the pith, and a peripheral region that appears continuous with the overlying peripheral zone (PZ) and gives rise to the epidermis, cortex, and vascular tissues of the stem (Sachs, 1965; Sanchez et al, 2012)
Growth of the different meristem regions can be controlled differentially: during the vegetative stage in Arabidopsis, the central zone (CZ) and PZ sustain leaf production but the RZ is inhibited, whereas at the transition to flowering, activation of the RZ leads to rapid stem elongation while the CZ and PZ start to produce floral buds
Summary
All plant growth is sustained by stem cell populations located within the apical meristems (Aichinger et al, 2012). The underlying rib zone (RZ) gives rise to the stem and includes a central region called the rib meristem (named after its distinct pattern of transversal cell divisions), which gives rise to the pith, and a peripheral region that appears continuous with the overlying PZ and gives rise to the epidermis, cortex, and vascular tissues of the stem (Sachs, 1965; Sanchez et al, 2012) Superimposed on this functional zonation, the shoot meristem has a layered structure; in angiosperms such as Arabidopsis, the cells in the outermost two to three layers divide mostly anticlinally (perpendicular to the meristem surface), so their descendants generally remain in the same layer (Fletcher, 2002). Growth of the different meristem regions can be controlled differentially: during the vegetative stage in Arabidopsis, the CZ and PZ sustain leaf production but the RZ is inhibited, whereas at the transition to flowering, activation of the RZ leads to rapid stem elongation while the CZ and PZ start to produce floral buds
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