Abstract Specification of new organs from transit amplifying cells is critical for higher eukaryote development. In plants, a central stem cell pool maintained by the pluripotency factor SHOOTMERISTEMLESS (STM), is surrounded by transit amplifying cells competent to respond to auxin hormone maxima by giving rise to new organs. Auxin triggers flower initiation through Auxin Response Factor (ARF) MONOPTEROS (MP) and recruitment of chromatin remodelers to activate genes promoting floral fate. The contribution of gene repression to reproductive primordium initiation is poorly understood. Here we show that downregulation of the STM pluripotency gene promotes initiation of flowers and uncover the mechanism for STM silencing. The ARFs ETTIN (ETT) and ARF4 promote organogenesis at the reproductive shoot apex in parallel with MP via histone-deacetylation mediated transcriptional silencing of STM . ETT and ARF4 directly repress STM , while MP acts indirectly, through its target FILAMENTOUS FLOWER ( FIL ). Our data suggest that – as in animals- downregulation of the pluripotency program is important for organogenesis in plants.
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What a tangled web it weaves: auxin coordination of stem cell maintenance and flower production
Robust agricultural yields require consistent flower production throughout fluctuating environmental conditions. Floral primordia are produced in the inflorescence meristem, which contains a pool of continuously dividing stem cells. Daughter cells of these divisions either retain stem cell identity or are pushed to the SAM periphery, where they become competent to develop into floral primordia after receiving the appropriate signal. Thus, flower production is inherently linked to regulation of the stem cell pool. The plant hormone auxin promotes flower development throughout its early phases and has been shown to interact with the molecular pathways regulating stem cell maintenance. Here, we will summarize how auxin signaling contributes to stem cell maintenance and promotes flower development through the early phases of initiation, outgrowth, and floral fate establishment. Recent advances in this area suggest that auxin may serve as a signal that integrates stem cell maintenance and new flower production.
more » « less- NSF-PAR ID:
- 10477288
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Journal of Experimental Botany
- Volume:
- 74
- Issue:
- 22
- ISSN:
- 0022-0957
- Format(s):
- Medium: X Size: p. 6950-6963
- Size(s):
- ["p. 6950-6963"]
- Sponsoring Org:
- National Science Foundation
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Abstract Sex types of papaya are controlled by a pair of nascent sex chromosomes, but molecular genetic mechanisms of sex determination and sex differentiation in papaya are still unclear. We performed comparative analysis of transcriptomic profiles of male and female floral buds at the early development stage before the initiation of reproductive organ primordia at which there is no morphological difference between male and female flowers. A total of 1734 differentially expressed genes (DEGs) were identified, of which 923 showed female-biased expression and 811 showed male-biased expression. Functional annotation revealed that genes related to plant hormone biosynthesis and signaling pathways, especially in abscisic acid and auxin pathways, were overrepresented in the DEGs. Transcription factor binding motifs, such as MYB2, GAMYB, and AP2/EREBP, were enriched in the promoters of the hormone-related DEGs, and transcription factors with those motifs also exhibited differential expression between sex types. Among these DEGs, we also identified 11 genes in the non-recombining region of the papaya sex chromosomes and 9 genes involved in stamen and carpel development. Our results suggested that sex differentiation in papaya may be regulated by multiple layers of regulation and coordination and involved transcriptional, epigenetic, and phytohormone regulation. Hormones, especially ABA and auxin, transcription factors, and genes in the non-recombination region of the sex chromosome could be involved in this process. Our findings may facilitate the elucidation of signal transduction and gene interaction in sex differentiation of unisexual flowers in papaya.
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Summary Phenological studies often focus on relationships between flowering date and temperature or other environmental variables. Yet in species that preform flowers, anthesis is one stage of a lengthy developmental process, and effects of temperature on flower development in the year(s) before flowering are largely unknown.
We investigated the effects of temperature during preformation on flower development in
Vaccinium vitis‐idaea . Using scanning electron microscopy, we established scores for developing primordia and examined effects of air temperature, depth of soil thaw, time of year and previous stage on development.Onset of flower initiation depends on soil thaw, and developmental change is greatest at early stages and during the warmest months. Regardless of temperature and time during the season, all basal floral primordia pause development at the same stage before whole‐plant dormancy.
Once primordia are initiated, development does not appear to be influenced by air temperature differences within the range of variation among our sites. There may be strong endogenous flower‐level controls over development, particularly the stage at which morphogenesis ceases before dormancy. However, the strength of such internal controls in the face of continuing temperature extremes under a changing climate is unclear.
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Abstract Improving yield by increasing the size of produce is an important selection criterion during the domestication of fruit and vegetable crops. Genes controlling meristem organization and organ formation work in concert to regulate the size of reproductive organs. In tomato,
lc andfas control locule number, which often leads to enlarged fruits compared to the wild progenitors.LC WUSCHEL (WUS ), whereasFAS CLAVATA 3 (CLV 3). The critical role of theWUS ‐CLV 3 feedback loop in meristem organization has been demonstrated in several plant species. We show that mutant alleles for both loci in tomato led to an expansion of theSl expression domain in young floral buds 2–3 days after initiation. Single and double mutant alleles ofWUS lc andfas maintain higherSl expression during the development of the carpel primordia in the floral bud. This augmentation and altered spatial expression ofWUS Sl provided a mechanistic basis for the formation of multilocular and large fruits. Our results indicated thatWUS lc andfas are gain‐of‐function and partially loss‐of‐function alleles, respectively, while both mutations positively affect the size of tomato floral meristems. In addition, expression profiling showed thatlc andfas affected the expression of several genes in biological processes including those involved in meristem/flower development, patterning, microtubule binding activity, and sterol biosynthesis. Several differentially expressed genes co‐expressed withSl have been identified, and they are enriched for functions in meristem regulation. Our results provide new insights into the transcriptional regulation of genes that modulate meristem maintenance and floral organ determinacy in tomato.WUS -
INTRODUCTION Balance between excitatory and inhibitory neuron (interneuron) populations in the cortex promotes normal brain function. Interneurons are primarily generated in the medial, caudal, and lateral ganglionic eminences (MGE, CGE, and LGE) of the ventral embryonic forebrain; these subregions give rise to distinct interneuron subpopulations. In rodents, the MGE generates cortical interneurons, the parvalbumin + (PV + ) and somatostatin + (SST + ) subtypes that connect with excitatory neurons to regulate their activity. Defects in interneuron production have been implicated in neurodevelopmental and psychiatric disorders including autism, epilepsy, and schizophrenia. RATIONALE How does the human MGE (hMGE) produce the number of interneurons required to populate the forebrain? The hMGE contains progenitor clusters distinct from what has been observed in the rodent MGE and other germinal zones of the human brain. This cytoarchitecture could be the key to understanding interneuron neurogenesis. We investigated the cellular and molecular properties of different compartments within the developing hMGE, from 14 gestational weeks (GW) to 39 GW (term), to study their contribution to the production of inhibitory interneurons. We developed a xenotransplantation assay to follow the migration and maturation of the human interneurons derived from this germinal region. RESULTS Within the hMGE, densely packed aggregates (nests) of doublecortin + (DCX + ) and LHX6 + cells were surrounded by nestin + progenitor cells and their processes. These DCX + cell–enriched nests (DENs) were observed in the hMGE but not in the adjacent LGE. We found that cells within DENs expressed molecular markers associated with young neurons, such as DCX, and polysialylated neural cell adhesion molecule (PSA-NCAM). A subpopulation also expressed Ki-67, a marker of proliferation; therefore, we refer to these cells as neuroblasts. A fraction of DCX + cells inside DENs expressed SOX2 and E2F1, transcription factors associated with progenitor and proliferative properties. More than 20% of DCX + cells in the hMGE were dividing, specifically within DENs. Proliferating neuroblasts in DENs persisted in the hMGE throughout prenatal human brain development. The division of DCX + cells was confirmed by transmission electron microscopy and time-lapse microscopy. Electron microscopy revealed adhesion contacts between cells within DENs, providing multiple sites to anchor DEN cells together. Neuroblasts within DENs express PCDH19, and nestin + progenitors surrounding DENs express PCDH10; these findings suggest a role for differential cell adhesion in DEN formation and maintenance. When transplanted into the neonatal mouse brain, dissociated hMGE cells reformed DENs containing proliferative DCX + cells, similar to DENs observed in the prenatal human brain. This suggests that DENs are generated by cell-autonomous mechanisms. In addition to forming DENs, transplanted hMGE-derived neuroblasts generated young neurons that migrated extensively into cortical and subcortical regions in the host mouse brain. One year after transplantation, these neuroblasts had differentiated into distinct γ-aminobutyric acid–expressing (GABAergic) interneuron subtypes, including SST + and PV + cells, that showed morphological and functional maturation. CONCLUSION The hMGE harbors DENs, where cells expressing early neuronal markers continue to divide and produce GABAergic interneurons. This MGE-specific arrangement of neuroblasts in the human brain is present until birth, supporting expanded neurogenesis for inhibitory neurons. Given the robust neurogenic output from this region, knowledge of the mechanisms underlying cortical interneuron production in the hMGE will provide insights into the cell types and developmental periods that are most vulnerable to genetic or environmental insults. Nests of DCX + cells in the ventral prenatal brain. Schematic of a coronal view of the embryonic human forebrain showing the medial ganglionic eminence (MGE, green), with nests of DCX + cells (DENs, green). Nestin + progenitor cells (blue) are present within the VZ and iSVZ and are intercalated in the oSVZ (where DENs reside). The initial segment of the oSVZ contains palisades of nestin + progenitors referred to as type I clusters (light blue cells) around DENs. In the outer part of the oSVZ, DENs transition to chains of migrating DCX + cells; surrounding nestin + progenitors are arranged into groups of cells referred to as type II clusters (white cells). In addition to proliferation of nestin + progenitors, cell division is present among DCX + cells within DENs, suggesting multiple progenitor states for the generation of MGE-derived interneurons in the human forebrain. ILLUSTRATION: NOEL SIRIVANSANTImore » « less
