Biology subjects

Gallavotti, A.

Publications and source records attributed to Gallavotti, A..

11 recordsLinked to original sources

bioRxiv2026

Specification of embryonic shoot stem cells via a small RNA-driven morphogenic circuit

The specification of embryonic stem cells capable of self-renewing and differentiation into virtually any cell type, is one of the most consequential events in the development of a multicellular organism. Yet the mechanisms establishing embryonic stem cell fate remain poorly understood, particularly in monocotyledonous cereals. Using the classic mutant leafbladeless1-raggedseedling1, we show that the small RNA tasiARF acts as a primary epidermis-derived morphogenic signal that organizes shoot stem cell specification in the maize embryo. tasiARF restricts expression of the AUXIN RESPONSE FACTOR 3 (ARF3) transcription factor, which modulates cell wall mechanics and guides the differential localization of PIN-FORMED (PIN) auxin efflux carriers, establishing a localized auxin minimum permissive for stem cell fate. Interestingly, loss of this auxin minimum and the associated shoot stem cell defects in tasiARF-deficient embryos are buffered by natural variation at a quantitative trait locus (QTL) controlling expression of MICROTUBULE-ASSOCIATED PROTEIN 65-3 (MAP65-3), a critical factor determining cell division orientation, which reshapes auxin dynamics and restores stem cell specification, and is itself under tasiARF-ARF3 control. Thus, embryonic shoot stem cell specification in maize is governed by an intricate morphogenic circuit that couples small RNA-mediated positional information to a self-stabilizing network interdependently linking cell wall mechanics, auxin signaling, and cell division patterning. This mechanistic framework reveals the redeployment of an ancient small RNA pathway as a lineage-specific innovation to establish a conserved, stem cell-permissive low auxin environment within the divergent embryonic architecture of monocotyledonous cereals. More broadly, it identifies molecular entry points for the engineering of embryogenic competence and regeneration capacity for the improvement of cereal crops.

plant biology↗

bioRxiv2024

Diversification and conservation of DNA binding specificities of SPL family of transcription factors

O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=89 SRC="FIGDIR/small/612952v2_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@1154c42org.highwire.dtl.DTLVardef@1419f5borg.highwire.dtl.DTLVardef@1454a7aorg.highwire.dtl.DTLVardef@1cbd5f_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGRAPHICAL ABSTRACTC_FLOATNO C_FIG SQUAMOSA Promoter-Binding Protein-Like (SPL) transcription factors are key regulators of plant development and stress responses. Here, we present a comprehensive DNA affinity purification sequencing (DAP-seq) analysis of 14 of the 16 SPL members in Arabidopsis thaliana, revealing two major classes based on distinct DNA-binding motifs. Gene Ontology enrichment of target genes indicated both shared and specialized functions among AtSPLs, including roles in hormone signaling, metal ion homeostasis, and developmental transitions. Comparative analysis of closely related paralogs, AtSPL9 and AtSPL15, uncovered divergence in their genomic binding locations and target gene regulation, particularly in auxin and abscisic acid pathways. These differences were supported by motif analysis and protoplast reporter assays. Extending our study across species, we analyzed DAP-seq data from maize (Zea mays) and wheat (Triticum aestivum) SPL homologs, identifying conserved target genes but species-specific DNA motifs. Notably, wheat SPLs preferentially bind to longer, palindromic motifs distinct from the GTAC core motif in Arabidopsis. Using AlphaFold3 structure modeling, we show that these motif differences may arise from enhanced protein-protein interactions that stabilize dimeric binding. Our results highlight how SPL family members diversify through DNA-binding evolution and suggest that transcription factor dimerization contributes to motif complexity and regulatory specialization across plant genomes.

plant biology↗

bioRxiv2024

Transcription factor binding site divergence across maize inbred lines drives transcriptional and phenotypic variation

Regulatory elements are important constituents of plant genomes that have shaped ancient and modern crops. Their identification, function, and diversity in crop genomes however are poorly characterized, thus limiting our ability to harness their power for further agricultural advances using induced or natural variation. Here, we use DNA affinity purification-sequencing (DAP-seq) to map transcription factor (TF) binding events for 200 maize TFs belonging to 30 distinct families and heterodimer pairs in two distinct inbred lines historically used for maize hybrid plant production, providing empirical binding site annotation for 5.3% of the maize genome. TF binding site comparison in B73 and Mo17 inbreds reveals widespread differences, driven largely by structural variation, that correlate with gene expression changes. TF binding site presence-absence variation helps clarify complex QTL such as vgt1, an important determinant of maize flowering time, and DICE, a distal enhancer involved in herbivore resistance. Modification of TF binding regions via CRISPR-Cas9 mediated editing alters target gene expression and phenotype. Our functional catalog of maize TF binding events enables collective and comparative TF binding analysis, and highlights its value for agricultural improvement.

plant biology↗

bioRxiv2024

WUSCHEL-dependent chromatin regulation in maize inflorescence development at single-cell resolution

WUSCHEL (WUS) is transcription factor vital for stem cell proliferation in plant meristems. In maize, ZmWUS1 is expressed in the inflorescence meristem, including the central zone, the reservoir of stem cells. ZmWUS1 overexpression in the Barren inflorescence3 mutant leads to defects in inflorescence development. Here, single-cell ATAC-seq analysis shows that ZmWUS1 overexpression alters chromatin accessibility throughout the central zone. The CAATAATGC motif, a known homeodomain recognition site, is predominantly observed in the regions with increased chromatin accessibility suggesting ZmWUS1 is an activator in the central zone. Regions with decreased chromatin accessibility feature various motifs and are adjacent to AUXIN RESPONSE FACTOR genes, revealing negative regulation of auxin signaling in the central zone. DAP-seq of ZmWUS1 identified the TGAATGAA motif, abundant in epidermal accessible chromatin compared to the central zone. These findings highlight ZmWUS1s context-dependent mechanisms for stem cell maintenance in the inflorescence meristem.

plant biology↗

bioRxiv2024

Mechanisms Of Meristem Maintenance By Maize Transcriptional Corepressors

The formation of the plant body proceeds in a sequential post-embryonic manner through the action of meristems. Tightly coordinated meristem regulation is required for development and reproductive success, eventually determining yield in crop species. In maize, the REL2 family of transcriptional corepressors includes four members, REL2, RELK1 (REL2-LIKE1), RELK2, and RELK3. In a screen for rel2 enhancers, we identified shorter double mutants with enlarged female inflorescence meristems (IMs) carrying mutations in RELK1. Expression and genetic analysis indicate that REL2 and RELK1 cooperatively regulate female IM development by controlling genes involved in redox balance, hormone homeostasis, and differentiation, ultimately tipping the meristem toward an environment favorable to expanded expression of the ZmWUSCHEL1 gene, a key stem-cell promoting transcription factor. We further demonstrate that RELK genes have partially redundant yet diverse functions in the maintenance of various meristem types during development. By exploiting subtle increases in ear IM size in rel2 heterozygous plants, we also show that extra rows of kernels are formed across a diverse set of F1 hybrids. Our findings reveal that the REL2 family maintains development from embryonic initiation to reproductive growth and can potentially be harnessed for increasing seed yield in a major crop species. One sentence summaryREL2-RELKs fine tune hormone and chemical cues to prevent expanded expression of ZmWUSCHEL1 in maize inflorescence meristems, and can potentially be harnessed for increasing seed yield in hybrids.

plant biology↗

bioRxiv2024

Large-scale single-cell profiling of stem cells uncovers redundant regulators of shoot development and yield trait variation

Stem cells in plant shoots are a rare population of cells that produce leaves, fruits and seeds, vital sources for food and bioethanol. Uncovering regulators expressed in these stem cells will inform crop engineering to boost productivity. Single-cell analysis is a powerful tool for identifying regulators expressed in specific groups of cells. However, accessing plant shoot stem cells is challenging. Recent single-cell analyses of plant shoots have not captured these cells, and failed to detect stem cell regulators like CLAVATA3 and WUSCHEL. In this study, we finely dissected stem cell-enriched shoot tissues from both maize and arabidopsis for single-cell RNA-seq profiling. We optimized protocols to efficiently recover thousands of CLAVATA3 and WUSCHEL expressed cells. A cross-species comparison identified conserved stem cell regulators between maize and arabidopsis. We also performed single-cell RNA-seq on maize stem cell overproliferation mutants to find additional candidate regulators. Expression of candidate stem cell genes was validated using spatial transcriptomics, and we functionally confirmed roles in shoot development. These candidates include a family of ribosome-associated RNA-binding proteins, and two families of sugar kinase genes related to hypoxia signaling and cytokinin hormone homeostasis. These large-scale single-cell profiling of stem cells provide a resource for mining stem cell regulators, which show significant association with yield traits. Overall, our discoveries advance the understanding of shoot development and open avenues for manipulating diverse crops to enhance food and energy security.

plant biology↗

bioRxiv2022

The combination of morphogenic regulators BABY BOOM and GRF-GIF improves maize transformation efficiency

Transformation is an indispensable tool for plant genetics and functional genomic studies. Although stable transformation no longer represents a major technology bottleneck in maize, there is still need for easily accessible and efficient transformation methods in most academic labs. Here we present the GGB transformation system, a rapid and highly efficient transformation system optimized for the immature embryo transformation of two maize genetic backgrounds, including the inbred line B104. The combination of distinct morphogenetic factors, the maize BABY BOOM transcriptional regulator (ZmBBM/EREB53) and the wheat GRF4-GIF1 (GROWTH REGULATING FACTOR4 - GRF-INTERACTING FACTOR1) chimera, together with a modified QuickCorn protocol, regenerated transformed maize seedlings in approximately two months with an efficiency of 26 to 37%; notably, the efficiency was 7-fold higher than with using either component in isolation. Additionally, ectopic expression of both morphogenetic factors did not show obvious effects on B104 development, and in particular fertility was not affected, obviating the need to remove the morphogenetic regulators post Agrobacterium infections. The GGB transformation system is designed for CRISPR-Cas9 editing but can be adapted for other purposes and should be easy to implement in most academic labs with little transformation experience.

plant biology↗

bioRxiv2022

Identifying transcription factor-DNA interactions using machine learning

Machine learning approaches have been applied to identify transcription factor (TF)-DNA interaction important for gene regulation and expression. However, due to the enormous search space of the genome, it is challenging to build models capable of surveying entire reference genomes, especially in species where models were not trained. In this study, we surveyed a variety of methods for classification of epigenomics data in an attempt to improve the detection for 12 members of the Auxin Response Factor (ARF) binding DNAs from maize and soybean as assessed by DNA Affinity Purification and sequencing (DAP-seq). We used the classification for prediction by minimizing the genome search space by only surveying unmethylated regions (UMRs). For identification of DAP-seq binding events within the UMRs, we achieved 93.54% accuracy, 6.2% false positive, and a 43.29% false negative rate across 12 members of ARFs of maize on average by encoding DNA with count vectorization for k-mer with a logistic regression classifier with up-sampling and feature selection. Importantly, feature selection helps to uncover known and potentially novel ARF binding motifs. This demonstrates an independent method for identification of transcription factor binding sites. Finally, we tested the model built with maize DAP-seq data and applied it directly to the soybean genome and found unacceptably high false positive rates, which accounted for more than 40% across the ARF TFs tested. The findings in this study suggest the potential use of various methods to predict TF-DNA interactions within and between species with varying degrees of success.

bioinformatics↗

bioRxiv2020

A cis-regulatory atlas in maize at single-cell resolution

Cis-regulatory elements (CREs) encode the genomic blueprints of spatiotemporal gene expression programs enabling highly specialized cell functions. To identify CREs at cell-type resolution in Zea mays, we implemented single-cell sequencing of Assay for Transposase Accessible Chromatin (scATAC-seq) in seedlings, embryonic roots, crown roots, axillary buds, and pistillate and staminate inflorescence. We describe 92 states of chromatin accessibility across 165,913 putative CREs and 52 known cell types. Patterns of transcription factor (TF) motif accessibility predicted cell identity with high accuracy, uncovered putative non-cell autonomous TFs, and revealed TF motifs underlying higher-order chromatin interactions. Comparison of maize and Arabidopsis thaliana developmental trajectories identified TF motifs with conserved patterns of accessibility. Cell type-specific CREs were enriched with enhancer activity, phenotype-associated genetic variants, and signatures of breeding-era selection. These data, along with companion software, Socrates, afford a comprehensive framework for understanding cellular heterogeneity, evolution, and cis-regulatory grammar of cell-type specification in a major crop.

genetics↗

bioRxiv2020

The FUSED LEAVES1/ADHERENT1 Regulatory Module Is Required For Maize Cuticle Development And Organ Separation

In land plants all aerial epidermal cells are covered by the cuticle, an extracellular hydrophobic layer. The cuticle represents a primary barrier between cells and the external environment, provides protection against abiotic and biotic stresses, and prevents organ fusion during development. Here we report the cloning and characterization of a classic mutant of maize called adherent1 (ad1), first described a century ago, and we show that AD1 encodes a 3-KETOACYL-CoA SYNTHASE involved in the deposition of cuticular wax on the epidermis of leaves and inflorescences. ad1 mutants show decreased amounts of various wax components as well as a range of organ fusion defects during vegetative and reproductive development. Accordingly, we find that AD1 is strongly expressed in the epidermis of various developing organs where it is directly regulated by the MYB transcription factor FUSED LEAVES1 (FDL1), which in turn controls a series of additional genes involved in cuticle formation. Altogether, our results identify a major pathway of cuticle biosynthesis essential for the development of maize plants, and a key regulatory module that is conserved across monocot and eudicot species. One sentence summaryThe classic maize mutant adherent1, first isolated a century ago, is affected in an enzyme responsible for cuticle formation that is regulated by the MYB transcription factor FUSED LEAVES1.

plant biology↗

bioRxiv2019

A synthetic approach reveals a highly sensitive maize auxin response circuit

Auxin plays a key role across all land plants in growth and developmental processes. Although auxin signaling function has diverged and expanded, differences in the molecular functions of signaling components have largely been characterized in Arabidopsis thaliana. Here, we used the Auxin Response Circuit recapitulated in Saccharomyces cerevisiae (ARCSc) system to functionally annotate maize auxin signaling components, focusing on genes expressed during development of ear and tassel inflorescences. All 16 maize Auxin (Aux)/Indole-3-Acetic Acid (IAA) repressor proteins are degraded in response to auxin, with rates that depended on both receptor and repressor identity. When fused to the maize TOPLESS (TPL) homolog RAMOSA1 ENHANCER LOCUS2 (REL2), maize Aux/IAAs were able to repress AUXIN RESPONSE FACTOR (ARF) transcriptional activity. A complete auxin response circuit comprised of all maize components, including ZmAFB2/3 b1 maize AUXIN SIGNALING F-BOX (AFB) receptor, was found to be fully functional. The ZmAFB2/3 b1 auxin receptor was found to be more sensitive to hormone than AtAFB2 and allowed for rapid circuit activation upon auxin addition. These results validate the conserved role of predicted auxin response genes in maize, as well as provide evidence that a synthetic approach can facilitate broader comparative studies across the wide range of species with sequenced genomes. A synthetic maize auxin response circuit is recapitulated in Saccharomyces cerevisiae, revealing a highly sensitive auxin signaling network with functional homology to the Arabidopsis circuit.

plant biology↗