Further Development 5.2: Specifying the Shoot and Root Meristems

Stem Cells: Their Potential and Their Niches

REV and PLT2 are differentially expressed transcription factors that cross-repress one another in a way that reinforces specification along a given path of meristem development. Remarkably, manipulation of PLT2 or REV expression can cause reversal of meristem fates. Specifically, loss of the PLT2 repressor TOPLESS fosters expanded PLT2 gene expression in the apical region of the embryo, which leads to a shoot-to-root conversion (Figure 1A, B). In contrast, misexpression of REV under the control of the PLT2 promoter produces a root-to-shoot conversion (Figure 1C) (Aida et al. 2004; Smith and Long 2010). These and other data support a model in which REV and PLT2 antagonize the gene regulatory networks for the root and shoot meristem, respectively (see Figure 5.5 A,B; Heidstra and Sabatini 2014; Gaillochet and Lohmann 2015).

Figure 1 Cross repression by transcription factor networks in embryonic shoot and root meristems. (A) Wild-type Arabidopsis thaliana embryo and seedling. PLT2 is expressed only in the root meristem in wild-type embryos. (B) TOPLESS functions to suppress PLT gene expression. Loss of TOPLESS results in expression of PLT genes in the apical region (red arrow), which converts the shoot meristem into a second root meristem, resulting in a second root (red arrowhead). (C) In contrast, misexpression of REV under the control of the PLT promoter in transgenic plants induces shoot meristematic gene expression in the presumptive root meristem cells (red arrow) that later results in basal-oriented shoot growth.

Literature Cited

Aida, M., D. Beis, R. Heidstra, V. Willemsen and I. Blilou. 2004. The PLETHORA genes mediate patterning of the Arabidopsis root stem cell niche. Cell 119: 109–120.

Gaillochet, C. and J. U. Lohmann. 2015. The never-ending story: from pluripotency to plant developmental plasticity. Development 142:2237–2249.

Heidstra, R. and S. Sabatini. 2014. Plant and animal stem cells: similar yet different. Nat. Rev. Mol. Cell. Biol. 15: 301–312.

Smith, Z. R. and J. A. Long. 2010. Control of Arabidopsis apical-basal embryo polarity by antagonistic transcription factors. Nature 464: 423–426.

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