Biology subjects

Monniaux, M.

Publications and source records attributed to Monniaux, M..

4 recordsLinked to original sources

bioRxiv2025

Spatial specificity of MADS-box transcription factors in floral organs

HighlightMADS-box transcription factors specify the identity of floral organs at the primordia stage, but they also have late and spatially-restricted roles in developing or mature floral organs, which we explore in this review. Floral homeotic genes, most of them encoding MADS-box transcription factors, are classically pictured as early specifiers of floral organ identity, as implied by the famous ABC model. Yet, floral homeotic genes remain expressed throughout floral organ development, sometimes with a cell type-specific expression pattern, and late functions have been firmly established for some of these genes. Here, we review how floral homeotic MADS-box genes are expressed in floral organs during their development, highlighting general trends for their spatial or temporal-specific expression, in particular for B-class genes in petals that are systematically distally-enriched. We focus on chosen examples from the literature to discuss the different roles associated with this specific expression, and we then explore the possible molecular mechanisms by which MADS-box transcription factors can adopt spatially or temporally restricted functions in floral organs, either by a simple restriction of their presence, or by a different mode of action in given cell types. Altogether, this review highlights that late roles of floral MADS-box transcription factors have been largely unexplored, and that these regulators might have multiple different functions according to the cell types in which they are present.

plant biology↗

bioRxiv2025

Interplay between petal identity and cell layer identity in petunia flowers

In flowering plants, floral organ identity is specified by the combinatorial action of homeotic genes. While the role of these genes in the early specification of organ identity is well established, their late function throughout floral organ development and in specific cell types is much less characterized. In particular, since plant organs are structured in clonally-independent cell layers, whether and how homeotic identity interacts with cell layer identity is unknown. We have previously identified cell layer-specific mutants for the petal identity gene PhDEF in petunia flowers, resulting in drastically different petal phenotypes whether PhDEF is expressed in the petal epidermis or in the mesophyll. In this study, using a combination of single-cell RNA-Seq and chromatin immunoprecipitation on phdef cell layer-specific mutants, we find that PhDEF regulates a different set of target genes in the petal epidermis and mesophyll, with a major regulatory action in the epidermis. We uncover a high diversity of binding profiles in PhDEF target genes, with a complex combination of layer-specific or non-specific binding sites, and a much more prominent binding of PhDEF in the epidermis than in the mesophyll. Our study highlights that floral homeotic genes like PhDEF can have different regulatory actions in different cell contexts, here different cell layers, demonstrating that cell layer identity indeed influences the regulatory processes underlying homeotic identity.

developmental biology↗

bioRxiv2025

Genomic architecture of the self-incompatibility locus in apple provides insights into the evolution of collaborative non-self recognition

Self-incompatibility (SI) systems prevent self-fertilization, thereby maintaining genetic diversity in flowering plants. Among them, collaborative non-self recognition (CNSR) is the most widespread, yet the genomic organization and evolutionary maintenance of its multigenic recognition system remain poorly understood. Using 27 haplotype-resolved genomes from wild and domesticated apples (Malus spp.), we dissected the structure and evolution of the S-locus. We identified 17 S-RNase alleles and 500 pollen-expressed S-locus F-box brother (SFBB) genes across 18 families. The S-locus shows extensive structural divergence among alleles and transposable element accumulation, consistent with long-term restricted effective recombination. Despite this divergence, haplotypes carrying the same S-RNase allele retain remarkably conserved SFBB repertoires and gene organization, even across species boundaries, indicating that long-term balancing selection preserves highly conserved S-haplotype architectures associated with specific S-RNase lineages. Tandem duplication, positive selection, and signatures consistent with gene conversion contribute to the diversification of pollen-expressed SFBB genes while S-RNase-associated SFBB repertoires remain conserved across haplotypes carrying the same S-RNase allele. Our results reveal how a structurally dynamic yet evolutionarily constrained genomic region can sustain long-term S-allele diversity and preserve complex multigenic haplotype architectures in flowering plants.

genomics↗

bioRxiv2021

Cell layer-specific expression of the B-class MADS-box gene PhDEF drives petal tube or limb development in petunia flowers

Floral homeotic MADS-box transcription factors ensure the correct morphogenesis of floral organs, which are organized in different cell layers deriving from the meristematic L1, L2 and L3 layers. How cells from these distinct layers acquire their respective identity and coordinate their growth to ensure normal floral organ morphogenesis is unresolved. Here, we study petunia petals that form a limb and tube through congenital fusion, a complex morphology that coevolved with pollinators. We have identified petunia mutants expressing the B-class MADS-box gene PhDEF in the epidermis or in the mesophyll of the petal only, called wico and star respectively. Strikingly, wico flowers form a strongly reduced tube while their limbs are almost normal, while star flowers form a normal tube but very reduced and unpigmented limbs, showing that petunia petal morphogenesis is highly modular. Comparative transcriptome analysis of star, wico and wild-type petals revealed a strong down-regulation of the anthocyanin production pathway in star petals including its major regulator ANTHOCYANIN2 (AN2). We found that PhDEF directly binds to AN2 regulatory sequence in vitro by gel shift assay, and in vivo by chromatin immunoprecipitation, suggesting that PhDEF directly activates the petal pigmentation pathway by activating AN2. Altogether, we show that cell-layer specific homeotic activity in petunia petals differently impacts tube and limb development, revealing the relative importance of the different cell layers in the modular architecture of petunia petals.

plant biology↗