A Mutation in the bHLH Domain of the SPCH Transcription Factor Uncovers a BR-Dependent Mechanism for Stomatal Development

The asymmetric cell divisions necessary for stomatal lineage initiation and progression in Arabidopsis (Arabidopsis thaliana) require the function of the basic helix-loop-helix (bHLH) transcription factor SPEECHLESS (SPCH). Mutants lacking SPCH do not produce stomata or lineages. Here, we isolated a...

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Bibliographic Details
Published in:Plant physiology (Bethesda) 2017-06, Vol.174 (2), p.823-842
Main Authors: de Marcos, Alberto, Houbaert, Anaxi, Triviño, Magdalena, Delgado, Dolores, Martín-Trillo, Mar, Russinova, Eugenia, Fenoll, Carmen, Mena, Montaña
Format: Article
Language:English
Subjects:
Arabidopsis - drug effects
Arabidopsis - genetics
Arabidopsis - physiology
Arabidopsis Proteins - genetics
Arabidopsis Proteins - metabolism
Basic Helix-Loop-Helix Transcription Factors - genetics
Basic Helix-Loop-Helix Transcription Factors - metabolism
Brassinosteroids - metabolism
Brassinosteroids - pharmacology
Cell Cycle Proteins - genetics
Cell Cycle Proteins - metabolism
Cell Differentiation
DNA-Binding Proteins - genetics
DNA-Binding Proteins - metabolism
FOCUS ISSUE ON STOMATA
Gene Expression Regulation, Plant
Hypocotyl - cytology
Mutation
Plant Leaves - cytology
Plant Leaves - genetics
Plant Stomata - cytology
Plant Stomata - drug effects
Plant Stomata - physiology
Plants, Genetically Modified
Protein Domains
Transcription Factors - genetics
Transcription Factors - metabolism
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Summary:The asymmetric cell divisions necessary for stomatal lineage initiation and progression in Arabidopsis (Arabidopsis thaliana) require the function of the basic helix-loop-helix (bHLH) transcription factor SPEECHLESS (SPCH). Mutants lacking SPCH do not produce stomata or lineages. Here, we isolated a new spch-5 allele carrying a point mutation in the bHLH domain that displayed normal growth, but had an extremely low number of sometimes clustered stomata in the leaves, whereas the hypocotyls did not have any stomata. In vivo tracking of leaf epidermal cell divisions, combined with marker lines and genetic analysis, showed that the spch-5 leaf phenotype is dosage dependent and results from the decreased ability to initiate and amplify lineages, defects in asymmetric cell fate allocation, and misorientation of asymmetric division planes. Notably, application of brassinosteroids (BRs) partly rescued the stomatal leaf phenotype of spch-5. Transcriptomic analysis combining spch-5 with BR treatments revealed that the expression of a set of SPCH target genes was restored by BRs. Our results also show that BR-dependent stomata formation and expression of some, but not all, SPCH target genes require the integrity of the bHLH domain of SPCH.
ISSN:0032-0889
1532-2548
DOI:10.1104/pp.17.00615