Abstract
Stem cell homeostasis in plant shoot meristems requires tight coordination between stem cell proliferation and cell differentiation. In Arabidopsis, stem cells express the secreted dodecapeptide CLAVATA3 (CLV3), which signals through the leucine-rich repeat (LRR)-receptor kinase CLAVATA1 (CLV1) and related CLV1-family members to downregulate expression of the homeodomain transcription factor WUSCHEL (WUS). WUS protein moves from cells below the stem cell domain to the meristem tip and promotes stem cell identity, together with CLV3 expression, generating a negative feedback loop. How stem cell activity in the meristem centre is coordinated with organ initiation and cell differentiation at the periphery is unknown. We show here that the CLE40 gene, encoding a secreted peptide closely related to CLV3, is expressed in the SAM in differentiating cells in a pattern complementary to that of CLV3. CLE40 promotes WUS expression via BAM1, a CLV1-family receptor, and CLE40 expression is in turn repressed in a WUS-dependent manner. Together, CLE40-BAM1-WUS establish a second negative feedback loop. We propose that stem cell homeostasis is achieved through two intertwined pathways that adjust WUS activity and incorporate information on the size of the stem cell domain, via CLV3-CLV1, and on cell differentiation via CLE40-BAM1.
Highlights
In angiosperms, the stem cell domain in shoot meristem is controlled by the directional interplay of two adjacent groups of cells
We propose that stem cell homeostasis is achieved through two intertwined pathways that adjust WUS activity and incorporate information on the size of the stem cell domain, via CLV3-CLV1, and on cell differentiation via CLE40-BAM1
CLE40 likely acts as an autocrine signal that is perceived by BAM1 in a domain flanking the organising centre (OC). Based on our findings, we propose a new model for the regulation of the stem cell domain in the shoot meristem in which signals and information from both, the central zone (CZ) and the peripheral zone (PZ) are integrated through two interconnected negative feedback loops that sculpt the dome-shaped shoot meristems of angiosperms
Summary
The stem cell domain in shoot meristem is controlled by the directional interplay of two adjacent groups of cells. These are the central zone (CZ) at the tip of the dome-shaped meristem, comprising slowly dividing stem cells, and the underlying cells of the organising centre (OC). Cells in the OC express the homeodomain transcription factor WUSCHEL (WUS), which moves through plasmodesmata to CZ cells to maintain stem cell fate and promote expression of the secreted signalling peptide CLAVATA3 (CLV3) (Brand et al, 2000; Daum et al, 2014; Müller et al, 2006; Schoof et al, 2000; Yadav et al, 2011). 2010; CS858348 Graf et al, 2010
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