Dataset Information

BHLH093/NFL and bHLH061 are required for apical meristem function in Arabidopsis thaliana.

ABSTRACT: The basic Helix-Loop-Helix (bHLH) transcription factors SCREAM/ICE1 and SCREAM2 have well-characterized roles in the terminal differentiation of stomatal guard cells in Arabidopsis thaliana. Here we report on the characterization of the functional roles of the remaining members of sub-group IIIB, bHLH093 and bHLH061. The bhlh093/bhlh061 double mutant failed to produce a primary inflorescence shoot and displayed greater phenotypic severity than bhlh093 and bhlh061 single mutants. An ultrastructural investigation revealed structural defects that develop in tissues surrounding the meristem prior to inflorescence emergence. The transition to flowering was restored in bhlh093/bhlh061 with the application of gibberellin to the apex. We also demonstrate that gibberellin application alleviates structural defects that develop in tissues surrounding the meristem and restore meristem activity. Furthermore, the bhlh093/bhlh061 double mutant was affected by delayed flowering, and the severity of the phenotype correlated with photoperiod and light intensity. Our results indicate that bHLH093 and bHLH061 function in the gibberellin-mediated establishment of functional apical meristems during the transition from vegetative to reproductive growth.

SUBMITTER: Poirier BC

PROVIDER: S-EPMC6128687 | biostudies-other | 2018

REPOSITORIES: biostudies-other

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bHLH093/NFL and bHLH061 are required for apical meristem function in Arabidopsis thaliana.

Poirier B C BC Feldman M J MJ Lange B M BM

Plant signaling & behavior 20180101 7

The basic Helix-Loop-Helix (bHLH) transcription factors SCREAM/ICE1 and SCREAM2 have well-characterized roles in the terminal differentiation of stomatal guard cells in Arabidopsis thaliana. Here we report on the characterization of the functional roles of the remaining members of sub-group IIIB, bHLH093 and bHLH061. The bhlh093/bhlh061 double mutant failed to produce a primary inflorescence shoot and displayed greater phenotypic severity than bhlh093 and bhlh061 single mutants. An ultrastructur ...[more]

PMID: 30160638

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Project description:BackgroundIn plants, the shoot apical meristem (SAM) has two main functions, involving the production of all aerial organs on the one hand and self-maintenance on the other, allowing the production of organs during the entire post-embryonic life of the plant. Transcription factors, microRNA, hormones, peptides and forces have been involved in meristem function. Whereas phosphatidylinositol phosphates (PIPs) have been involved in almost all biological functions, including stem cell maintenance and organogenesis in animals, the processes in meristem biology to which PIPs contribute still need to be delineated.ResultsUsing biosensors for PI4P and PI(4,5)P2, the two most abundant PIPs at the plasma membrane, we reveal that meristem functions are associated with a stereotypical PIP tissue-scale pattern, with PI(4,5)P2 always displaying a more clear-cut pattern than PI4P. Using clavata3 and pin-formed1 mutants, we show that stem cell maintenance is associated with reduced levels of PIPs. In contrast, high PIP levels are signatures for organ-meristem boundaries. Interestingly, this pattern echoes that of cortical microtubules and stress anisotropy at the meristem. Using ablations and pharmacological approaches, we further show that PIP levels can be increased when the tensile stress pattern is altered. Conversely, we find that katanin mutant meristems, with increased isotropy of microtubule arrays and slower response to mechanical perturbations, exhibit reduced PIP gradients within the SAM. Comparable PIP pattern defects were observed in phospholipase A3β overexpressor lines, which largely phenocopy katanin mutants at the whole plant level.ConclusionsUsing phospholipid biosensors, we identified a stereotypical PIP accumulation pattern in the SAM that negatively correlates with stem cell maintenance and positively correlates with organ-boundary establishment. While other cues are very likely to contribute to the final PIP pattern, we provide evidence that the patterns of PIP, cortical microtubules and mechanical stress are positively correlated, suggesting that the PIP pattern, and its reproducibility, relies at least in part on the mechanical status of the SAM.

Project description:The study of the concerted action of hormones and transcription factors is fundamental to understand cell differentiation and pattern formation during organ development. The root apical meristem of Arabidopsis thaliana is a useful model to address this. It has a stem cell niche near its tip conformed of a quiescent organizer and stem or initial cells around it, then a proliferation domain followed by a transition domain, where cells diminish division rate before transiting to the elongation zone; here, cells grow anisotropically prior to their final differentiation towards the plant base. A minimal model of the gene regulatory network that underlies cell-fate specification and patterning at the root stem cell niche was proposed before. In this study, we update and couple such network with both the auxin and cytokinin hormone signaling pathways to address how they collectively give rise to attractors that correspond to the genetic and hormonal activity profiles that are characteristic of different cell types along A. thaliana root apical meristem. We used a Boolean model of the genetic-hormonal regulatory network to integrate known and predicted regulatory interactions into alternative models. Our analyses show that, after adding some putative missing interactions, the model includes the necessary and sufficient components and regulatory interactions to recover attractors characteristic of the root cell types, including the auxin and cytokinin activity profiles that correlate with different cellular behaviors along the root apical meristem. Furthermore, the model predicts the existence of activity configurations that could correspond to the transition domain. The model also provides a possible explanation for apparently paradoxical cellular behaviors in the root meristem. For example, how auxin may induce and at the same time inhibit WOX5 expression. According to the model proposed here the hormonal regulation of WOX5 might depend on the cell type. Our results illustrate how non-linear multi-stable qualitative network models can aid at understanding how transcriptional regulators and hormonal signaling pathways are dynamically coupled and may underlie both the acquisition of cell fate and the emergence of hormonal activity profiles that arise during complex organ development.

Dataset Information

BHLH093/NFL and bHLH061 are required for apical meristem function in Arabidopsis thaliana.

Publications

bHLH093/NFL and bHLH061 are required for apical meristem function in Arabidopsis thaliana.

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