Shoot Apical Meristem Form and Function
The shoot apical meristem (SAM) generates above-ground aerial organs throughout the lifespan of higher plants. In order to fulfill this function, the meristem must maintain a balance between the self-renewal of a reservoir of central stem cells and organ initiation from peripheral cells. The activity of the pluripotent stem cell population in the SAM is dynamically controlled by complex, overlapping signaling networks that include the feedback regulation of meristem maintenance genes and the signaling of plant hormones. Organ initiation likewise requires the function of multifactor gene regulatory networks, as well as instructive cues from the plant hormone auxin and reciprocal signals from the shoot meristem. Floral meristems (FMs) are products of the reproductive SAM that sustains a transient stem cell reservoir for flower formation. Regulation of FM activity involves both feedback loops shared with the SAM and floral-specific factors. Recent studies have rapidly advanced our understanding of SAM function by adopting newly developed molecular and computational techniques. These advances are becoming integrated with data from traditional molecular genetics methodologies to develop a framework for understanding the central principles of SAM function.
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- "Many types of small peptides are involved in communication between cells and between functional domains within tissues and organs to regulate developmental processes such as stem cell maintenance , vascular differentiation, and stomatal development . In Arabidopsis thaliana, stem cell maintenance in the shoot apical meristem is negatively regulated by a CLAVATA3 (CLV3) CLE peptide, which acts through receptor complexes such as CLV1, CLV2/CRN, and RPK2 (reviewed in Aichinger et al., 2012; Ha et al., 2010; Miyawaki et al., 2013). Mutation in CLV3 leads to an enlarged meristem consisting of over-proliferated stem cells, due to a failure in the repression of WUSCHEL (WUS) activity, which promotes stem cell identity (Fletcher et al., 1999). "
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ABSTRACT: Peptide signaling plays important roles in various developmental processes of plants. Genes encoding CLE proteins, which are processed into CLE signaling peptides, are required for maintenance of the shoot apical meristem and for vascular differentiation. FON2-LIKE CLE PROTEIN1 (FCP1), a member of the CLE gene family, negatively regulates meristem maintenance in both shoot and root apical meristems of rice (Oryza sativa). Here, we examined the role of FCP1 in leaf development. We found that overexpression of FCP1 affects various aspects of leaf development in shoots regenerated from calli, making it difficult to distinguish between the leaf blade and leaf sheath. Differentiation of tissues such as vascular bundle and sclerenchyma was strongly inhibited by FCP1 overexpression. Spatial expression patterns of developmental genes DROOPING LEAF (DL) and OsPINHEAD1 (OsPNH1) were severely affected in the FCP1-overexpressing shoots. Whereas DL was expressed in the central region of leaf primordia in control shoots, DL expression was expanded throughout the leaf primordia of the FCP1-overexpressing shoots in early developmental stages. By contrast, OsPNH1, which is expressed in provascular and developing vascular tissues in normal seedlings, was strongly repressed by FCP1 overexpression. Taken together, our results suggest that FCP1 is involved in the regulation of cell fate determination during leaf development.
Available from: Bastiaan Bargmann
- "indole-3-butyric acid, phenylacetic acid and 4-chloroindole-3-acetic acid) (Simon and Petrasek 2011 for review). Auxin distribution is highly regulated, especially within the embryo and growth centers of the apical and cambial meristems where auxin concentration gradients are formed that guide cellular differentiation (see Bhalerao and Bennett 2003, Abbreviations – ABP1, AUXIN BINDING PROTEIN 1; AFB1–5, AUXIN SIGNALING F-BOX PROTEIN 1 through 5; ARF, AUXIN RESPONSE FACTOR; AtPGP4, P-GLYCOPROTEIN 4; AUX1, AUXIN RESISTANT 1; Aux/IAA, AUXIN/INDOLE-3-ACETIC ACID INDUCIBLE; AuxRE, auxin response elements; GH3, GRETCHEN HAGEN 3; IAA, indole-3-acetic acid; LAX, LIKE AUXIN RESISTANT; LRR, leucine-rich repeat; NRT1.1, NITRATE TRANSPORTER 1; PIN, PINFORMED; SCF, S-PHASE KINASE-ASSOCIATED PROTEIN 1 -CULLIN -F-BOX; TIR1, TRANSPORT INHIBITOR RESISTANT 1. Bennett and Scheres 2010, Ha et al. 2010, Peris et al. 2010 for reviews). Furthermore, auxin distribution is dynamically modified in response to external stimuli such as light or gravity (Swarup et al. 2005, Ding et al. 2011). "
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ABSTRACT: Auxin signaling through the SCFTIR1-Aux/IAA-ARF pathway is one of the best-studied plant hormone response pathways. Components of this pathway, from receptors through to transcription factors, have been identified and analyzed in detail. Although we understand elementary aspects of how the auxin signal is perceived and leads to a transcriptional response, many questions remain about the in vivo function of the pathway. Two crucial issues are the tissue-specificity of the response, i.e. how distinct cell types can interpret the same auxin signal differently, and the response to a signaling gradient, i.e. how a graded distribution of auxin can elicit distinct expression patterns along its range. Here, we speculate on how signaling through the canonical SCFTIR1-Aux/IAA-ARF pathway may achieve divergent responses.
Available from: Etienne Couturier
- "Similarly, some methods of mechanical perturbation, such as laser ablation, also involve wounding of the tissue (Hamant et al., 2008; Heisler et al., 2010). Plants are able to detect and respond to being wounded. "
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ABSTRACT: Morphogenesis does not just require the correct expression of patterning genes; these genes must induce the precise mechanical
changes necessary to produce a new form. Mechanical characterization of plant growth is not new; however, in recent years,
new technologies and interdisciplinary collaborations have made it feasible in young tissues such as the shoot apex. Analysis
of tissues where active growth and developmental patterning are taking place has revealed biologically significant variability
in mechanical properties and has even suggested that mechanical changes in the tissue can feed back to direct morphogenesis.
Here, an overview is given of the current understanding of the mechanical dynamics and its influence on cellular and developmental
processes in the shoot apex. We are only starting to uncover the mechanical basis of morphogenesis, and many exciting questions
remain to be answered.
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