Arabidopsis homologs of the Petunia HAIRY MERISTEM gene are required for maintenance of shoot and root indeterminacy

Biology Department, College of William and Mary, Williamsburg, Virginia 23187-8795, USA.
Plant physiology (Impact Factor: 6.84). 02/2011; 155(2):735-50. DOI: 10.1104/pp.110.168757
Source: PubMed


Maintenance of indeterminacy is fundamental to the generation of plant architecture and a central component of the plant life strategy. Indeterminacy in plants is a characteristic of shoot and root meristems, which must balance maintenance of indeterminacy with organogenesis. The Petunia hybrida HAIRY MERISTEM (HAM) gene, a member of the GRAS family of transcriptional regulators, promotes shoot indeterminacy by an undefined non-cell-autonomous signaling mechanism(s). Here, we report that Arabidopsis (Arabidopsis thaliana) mutants triply homozygous for knockout alleles in three Arabidopsis HAM orthologs (Atham1,2,3 mutants) exhibit loss of indeterminacy in both the shoot and root. In the shoot, the degree of penetrance of the loss-of-indeterminacy phenotype of Atham1,2,3 mutants varies among shoot systems, with arrest of the primary vegetative shoot meristem occurring rarely or never, secondary shoot meristems typically arresting prior to initiating organogenesis, and inflorescence and flower meristems exhibiting a phenotypic range extending from wild type (flowers) to meristem arrest preempting organogenesis (flowers and inflorescence). Atham1,2,3 mutants also exhibit aberrant shoot phyllotaxis, lateral organ abnormalities, and altered meristem morphology in functioning meristems of both rosette and inflorescence. Root meristems of Atham1,2,3 mutants are significantly smaller than in the wild type in both longitudinal and radial axes, a consequence of reduced rates of meristem cell division that culminate in root meristem arrest. Atham1,2,3 phenotypes are unlikely to reflect complete loss of HAM function, as a fourth, more distantly related Arabidopsis HAM homolog, AtHAM4, exhibits overlapping function with AtHAM1 and AtHAM2 in promoting shoot indeterminacy.

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Available from: Ross Sozzani, Dec 08, 2014
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    • "Other TFs involved in organ development are also grouped together in the TFsNet. For example, the closely related ATHAM1 (AT2G45160), ATHAM2 (AT3G60630) and ATHAM3 (AT4G00150) genes, belonging to the GRAS family, are involved in the maintenance of meristem indeterminacy, and are functionally redundant [47,48]. These three TFs also group in the same module in the TFsNet that we inferred (Figure 1e). "
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    BMC Plant Biology 04/2014; 14(1):97. DOI:10.1186/1471-2229-14-97 · 3.81 Impact Factor
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    • "The finding that the IDS was independent of auxin gradients in this study is in agreement with the absence of changes in auxin tissue content in A. thaliana seedlings treated with an inhibitor of THF biosynthesis (Stokes et al., 2013). RAM exhaustion of the A. thaliana triple mutant in the GRAS transcription factors HAIRY MERISTEM1, 2, and 3, which also has root determinacy, is similarly independent of auxin gradients (Engstrom et al., 2011). Nevertheless, we cannot exclude a link between folate metabolism and auxin signaling, specifically in the QC. "
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    New Phytologist 03/2014; 202(4). DOI:10.1111/nph.12757 · 7.67 Impact Factor
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    • "NAC proteins play diverse roles in a wide range of plant developmental processes, such as embryo development, shoot apical meristem development [22], [23], lateral root development [24], and hormone signaling [24], [25], [26]. HAM (hairy meristem), a member of GRAS family, regulates both shoot and root meristems [27]. Our results strongly suggested that formation of embryonic callus from the shoot apical meristem and hairy phenotype of the callus in LEC2 transgenic tobacco seedlings was correlated with up-regulation of HAM. "
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