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Abstract The Arabidopsis (Arabidopsis thaliana) TRANSPARENT TESTA GLABRA2 (TTG2) gene encodes a WRKY transcription factor that regulates a range of development events like trichome, seed coat, and atrichoblast formation. Loss-of-function of TTG2 was previously shown to reduce or eliminate trichome specification and branching. Here, we report the identification of an allele of TTG2, ttg2-6. In contrast to the ttg2 mutants described before, ttg2-6 displayed unique trichome phenotypes. Some ttg2-6 mutant trichomes were hyper-branched, whereas others were hypo-branched, distorted, or clustered. Further, we found that in addition to specifically activating R3 MYB transcription factor TRIPTYCHON (TRY) to modulate trichome specification, TTG2 also integrated cytoskeletal signaling to regulate trichome morphogenesis. The ttg2-6 trichomes displayed aberrant cortical microtubules (cMTs) and actin filaments (F-actin) configurations. Moreover, genetic and biochemical analyses showed that TTG2 could directly bind to the promoter and regulate the expression of BRICK1 (BRK1), which encodes a subunit of the actin nucleation promoting complex suppressor of cyclic AMP repressor (SCAR)/Wiskott–Aldrich syndrome protein family verprolin homologous protein (WAVE). Collectively, taking advantage of ttg2-6, we uncovered a function for TTG2 in facilitating cMTs and F-actin cytoskeleton-dependent trichome development, providing insight into cellular signaling events downstream of the core transcriptional regulation during trichome development in Arabidopsis.
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A eudicot MIXTA family ancestor likely functioned in both conical cells and trichomes
TheMIXTAfamily of MYB transcription factors modulate the development of diverse epidermal features in land plants. This study investigates the evolutionary history and function of theMIXTAgene family in the early-diverging eudicot model lineageThalictrum(Ranunculaceae), with R2R3 SBG9-A MYB transcription factors representative of the pre-core eudicot duplication and thus hereby referred to as “paleoMIXTA” (PMX). Cloning and phylogenetic analysis ofThalictrum paleoMIXTA(ThPMX) orthologs across 23 species reveal a genus-wide duplication coincident with a whole-genome duplication. Expression analysis by qPCR confirmed that the highest expression is found in carpels, while newly revealing high expression in leaves and nuanced differences between paralogs in representative polyploid species. The single-copy ortholog from the diploid speciesT. thalictroides(TthPMX, previouslyTtMYBML2), which has petaloid sepals with conical–papillate cells and trichomes on leaves, was functionally characterized by virus-induced gene silencing (VIGS), and its role in leaves was also assessed from heterologous overexpression in tobacco. Another ortholog from a species with conical–papillate cells on stamen filaments,TclPMX, was also targeted for silencing. Overexpression assays in tobacco provide further evidence that thepaleoMIXTAlineage has the potential for leaf trichome function in a core eudicot. Transcriptome analysis by RNA-Seq on leaves of VIGS-treated plants suggests thatTthPMXmodulates leaf trichome development and morphogenesis through microtubule-associated mechanisms and that this may be a conserved pathway for eudicots. These experiments provide evidence for a combined role forpaleoMIXTAorthologs in (leaf) trichomes and (floral) conical–papillate cells that, together with data from other systems, makes the functional reconstruction of a eudicot ancestor most likely as also having a combined function.
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- Award ID(s):
- 1911539
- PAR ID:
- 10493839
- Publisher / Repository:
- Frontiers
- Date Published:
- Journal Name:
- Frontiers in Plant Science
- Volume:
- 14
- ISSN:
- 1664-462X
- Subject(s) / Keyword(s):
- epidermis MIXTA family non-core eudicots polyploidy trichomes conical cells ranunculid R2R3 MYB
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fpls.2023.1288961
