Academic literature on the topic 'Axillary meristem fate'

Above-ground plant architecture is dictated to a large extent by the fates and growth rates of aerial plant meristems. Shoot apical meristem gives rise to the fundamental plant form by generating new leaves. However, the fates of axillary meristems located in leaf axils have a great influence on plant architecture and affect the harvest index, yield potential and cultural practices. Improving plant architecture by breeding facilitates denser plantations, better resource use efficiency and even mechanical harvesting. Knowledge of the genetic mechanisms regulating plant architecture is needed for precision breeding, especially for determining feasible breeding targets. Fortunately, research in many crop species has demonstrated that a relatively small number of genes has a large effect on axillary meristem fates. In this review, we select a number of important horticultural and agricultural plant species as examples of how changes in plant architecture affect the cultivation practices of the species. We focus specifically on the determination of the axillary meristem fate and review how plant architecture may change even drastically because of altered axillary meristem fate. We also explain what is known about the genetic and environmental control of plant architecture in these species, and how further changes in plant architectural traits could benefit the horticultural sector.

Almond (Prunus dulcis [Mill.] D.A. Webb) represents a model system for the study of epigenetic age-related disorders in perennial plants because the economically important noninfectious bud-failure disorder is well characterized and shown to be associated with the clonal-age of the propagation source. Epigenetic changes regulating disorders such as changes in methylation or telomere-length shortening would be expected to occur in shoot apical meristem initial cells since subsequent daughter cells including those in ensuing shoot axillary meristems show an irreversible advance in epigenetic aging. Because multiple initial cells are involved in meristem development and growth, such ‘mutations’ would be expected to occur in some initial cells but not others, resulting in mericlinal or sectorial chimeras during subsequent shoot development that, in turn, would differentially affect vegetative buds present in the leaf axils of the shoot. To test this developmental pattern, 2180 trees propagated from axillary buds of known position within asymptomatic noninfectious bud-failure budstick sources were evaluated for the disorder. Results demonstrate that relative bud position was not a determinant of successful trait propagation, but rather all axillary buds within individual shoots showed very similar degrees of noninfectious bud-failure. Control is thus more analogous to tissue-wide imprinting rather than being restricted to discrete cell lineages as would be predicted by standard meristem cell fate-mapping.

Seeds of Arabidopsis thaliana, heterozygous for the alb1 mutation were treated with X-rays to generate sectors of albino tissue in the mature plants. Sectors were observed in tissues derived from L2 and L3 layers of the shoot meristem. Altogether 324 sectors were obtained affecting 512 leaves or the inflorescence. The majority of sectors affected only one or other of the first leaf pair. In later leaves, sectors were less frequent, and often affected more than one leaf. Sectors seen in the flowers almost invariably included some of the cauline leaves. Sectors in any region of the plant were of variable length and width. The axillary meristems of Arabidopsis were found to be clonally related to two or more cells near the centre of the subtending leaf. Overall the data are compatible with the idea that there are few, if any, restrictions on cell fate within the cell layers of the dry seed meristem. As in other higher plants, developmental fate could only be predicted in a general and probabilistic way. Such a pattern might be generated if the acquisition of cell fate occurred continuously as the plant grows, in a position-dependent, lineage-independent fashion. A general model of the meristem has been produced to accommodate the observations concerning the great majority of the sectors.

We have mapped the fate of cells in the Arabidopsis embryonic shoot apical meristem by irradiating seed and scoring the resulting clonally derived sectors. 176 white, yellow, pale green or variegated sectors were identified and scored for their position and extent in the resulting plants. Most sectors were confined to a fraction of a leaf, and only occasionally extended into the inflorescence. Sectors that extended into the inflorescence were larger, and usually encompassed about a third to a half of the inflorescence circumference. We also find that axillary buds in Arabidopsis are clonally related to the subtending leaf. Sections through the dry seed embryo indicate that the embryonic shoot apical meristem contains approximately 110 cells in the three meristematic layers prior to the formation of the first two leaf primordia. The histological analysis of cell number in the shoot apical meristem, in combination with the sector analysis have been used to construct a map of the probable fate of cells in the embryonic shoot apical meristem.

Shoot apical meristems (SAMs) of seed plants are small groups of pluripotent cells responsible for making leaves, stems and flowers. While the primary SAM forms during embryogenesis, new SAMs, called axillary SAMs, develop later on the body of the plant and give rise to branches. In Arabidopsis plants, axillary SAMs develop in close association with the adaxial leaf base at the junction of the leaf and stem (the leaf axil). We describe the phenotype caused by the Arabidopsis phabulosa-1d (phb-1d) mutation. phb-1d is a dominant mutation that causes altered leaf polarity such that adaxial characters develop in place of abaxial leaf characters. The adaxialized leaves fail to develop leaf blades. This supports a recently proposed model in which the juxtaposition of ad- and abaxial cell fates is required for blade outgrowth. In addition to the alteration in leaf polarity, phb-1d mutants develop ectopic SAMs on the undersides of their leaves. Also, the phb-1d mutation weakly suppresses the shoot meristemless (stm) mutant phenotype. These observations indicate an important role for adaxial cell fate in promoting the development of axiallary SAMs and suggest a cyclical model for shoot development: SAMs make leaves which in turn are responsible for generating new SAMs.

Axillary meristem fate patterns along shoots, also referred to as shoot structure, appear to be fairly consistent among trees within a genotype growing under similar conditions. Less is known about shoot structural plasticity following external manipulations, such as pruning. The aim of this study on almond (Prunus dulcis (Mill.)) shoots was to investigate how pruning severity affects the structure of 1-year-old shoots that grew after pruning (regrowth shoots), the 2-year-old portion of shoots that remained from the previous year’s growth after pruning (pruned shoots), and whether regrowth shoots reiterate the structure of the original 1-year-old shoots before pruning. Three pruning severities were imposed and the structures along the different shoots were assessed by building hidden semi-Markov models of axillary meristem fates. The structures of regrowth and pruned shoots depended on pruning severity, but maintained some of the original shoot characteristics. Regrowth shoots developed more complex structures with severe pruning, but had simpler structures than original shoots indicating progressive simplification with tree age. Pruned shoot structures were affected by the severity of pruning, by the structure when the shoots were 1 year old, and probably by local competition among buds. Changes in structure due to pruning can be modelled and be predictable.

Axillary and floral meristems are shoot meristems that initiate postembryonically. In Arabidopsis, axillary meristems give rise to branches during vegetative development while floral meristems give rise to flowers during reproductive development. This review compares the development of these meristems from their initiation at the shoot apical meristem up to the establishment of their specific developmental fates. Axillary and floral meristems originate from lateral primordia that form at flanks of the shoot apical meristem. Initial development of vegetative and reproductive primordia are similar, resulting in the formation of a morphologically defined primordium partitioned into adaxial and abaxial domains. The adaxial primordial domain is competent to form a meristem, while the abaxial domain correlates with the formation of a leaf. This review proposes that all primordia partition into domains competent to form the meristem and the leaf. According to this model, a vegetative primordium develops as leaf-bias while a reproductive primordium develops as meristem-bias.Key words: SHOOTMERISTEMLESS, LATERAL SUPPRESSOR, AINTEGUMENTA, adaxial primordial domain, abaxial primordial domain, shoot morphogenesis.

Le fraisier est capable de se reproduire de manière sexuée, via la floraison, et de manière asexuée, via la production de stolons. Ces deux modes de reproduction sont en compétition au niveau du méristème axillaire (MAx), qui peut devenir soit une branche latérale pouvant se terminer par une inflorescence, soit un stolon ou soit rester dormant. Ainsi, jouer sur le devenir du MAx modifie l’architecture de la plante et favorise le rendement soit en fruits soit en plants filles. L’objectif de la thèse est d’identifier et de caractériser des acteurs influençant le devenir d’un MAx en branche latérale ou en stolon en utilisant comme modèle le fraisier diploïde. Il se décline en trois points :(1) L’observation morphologique et histologique des évènements précoces du développement du MAx a permis de définir pour la première fois chez le fraisier une échelle de développement du MAx en stolon ou en branche latérale. Cette étude met en évidence un stade indifférencié, morphologiquement identique entre les deux devenirs possibles.(2) L’étude du transcriptome de bourgeons axillaires indifférenciés a permis d’identifier 283 gènes différentiellement exprimés (DEG) entre ceux qui vont devenir un stolon et ceux qui vont devenir une branche latérale. Parmi les DEG, certains gènes comme FveTCP9, homologue de AtBRC1, ainsi que des gènes impliqués dans la voie des phytohormones et de la floraison ont été identifiés et sélectionnés pour d’autres analyses afin d’approfondir leur rôle dans le devenir du MAx. Afin d’initier un réseau de gènes, une seconde analyse transcriptomique a pris en compte le développement spatio-temporel du bourgeon axillaire en branche latérale ou en stolon. Les effets de la position du bourgeon axillaire au niveau du nœud de l’axe primaire et du stade de développement de la plantule sur le transcriptome ont été mis en évidence.(3) Des analyses d’expression par qPCR sur des fonds génétiques différents et/ou hybridation in situ ont permis de confirmer l’implication des DEG sélectionnés dans le contrôle du devenir du MAx. Parmi ces gènes, les mutations obtenues par CRISPR-Cas9 sur FveTVP9 ont permis de valider son rôle dans le déterminisme du MAx grâce la production de branches latérales aux dépens des stolons.Cette thèse a permis d’initier un réseau de régulation contrôlant le devenir du MAx et également, de mettre en évidence des gènes clés qui pourront être étudiés chez le fraisier cultivé octoploïde à des fins agronomiques
Strawberry is able to reproduce both sexually, via flowering, and asexually, via the production of stolons. The AxM governs these two modes of reproduction since AxM can become a lateral branch terminated by an inflorescence, or a stolon, or remain dormant. Thus, the AxM fate shapes the plant architecture and promotes the fruit yield or daughter plant production. The objective of this thesis is to identify and characterise molecular actors that affect the AxM fate by using the diploid strawberry model. The manuscript is divided into three points:(1) Morphological and histological observation of the early events of the AxM development has allowed to define for the first time in strawberry a scale of the AxM development into a stolon or a lateral branch. This study highlights an undifferentiated stage that is morphologically identical for both types of AxM.(2) A transcriptome study of undifferentiated axillary buds identified 283 differentially expressed genes (DEGs) between those becoming a stolon and becoming a lateral branch. Among the DEGs, we identified FveTCP9, homologous to AtBRC1, and genes involved in the phytohormone and flowering pathways. These genes were chosen for further analysis to investigate their role in the AxM fate.In order to initiate a gene network, a second transcriptomic analysis included the spatio-temporal development of the axillary bud into a lateral branch or a stolon. Results highlighted the effects of the axillary bud position at the node of the primary crown and the developmental stage of the seedling on the transcriptome.(3) The study of the chosen DEGs by using different approaches, qPCR in different genetic backgrounds and/or in situ hybridization, confirmed their role in controlling the AxM fate. Among these genes, the CRISPR-Cas9 mutation of FveTCP9 validates its role in the AXM fate and shows that lateral branches were produced at the expense of stolons.This thesis initiated a regulatory network controlling the fate of MAx and also identified key genes that could be studied in octoploid strawberry for future agronomic applications

The shoot apical meristem establishes plant architecture by continuously producing new lateral organs such as leaves, axillary meristems and flowers throughout the plant life cycle. This unique capacity is achieved by a group of self-renewing pluripotent stem cells that give rise to founder cells, which can differentiate into multiple cell and tissue types in response to environmental and developmental cues. Cell fate specification at the shoot apical meristem is programmed primarily by transcription factors acting in a complex gene regulatory network. In this project we proposed to provide significant understanding of meristem maintenance and cell fate specification by studying four transcription factors acting at the meristem. Our original aim was to identify the direct target genes of WUS, STM, KNAT6 and CNA transcription factor in a genome wide scale and the manner by which they regulate their targets. Our goal was to integrate this data into a regulatory model of cell fate specification in the SAM and to identify key genes within the model for further study. We have generated transgenic plants carrying the four TF with two different tags and preformed chromatin Immunoprecipitation (ChIP) assay to identify the TF direct target genes. Due to unforeseen obstacles we have been delayed in achieving this aim but hope to accomplish it soon. Using the GR inducible system, genetic approach and transcriptome analysis [mRNA-seq] we provided a new look at meristem activity and its regulation of morphogenesis and phyllotaxy and propose a coherent framework for the role of many factors acting in meristem development and maintenance. We provided evidence for 3 different mechanisms for the regulation of WUS expression, DNA methylation, a second receptor pathway - the ERECTA receptor and the CNA TF that negatively regulates WUS expression in its own domain, the Organizing Center. We found that once the WUS expression level surpasses a certain threshold it alters cell identity at the periphery of the inflorescence meristem from floral meristem to carpel fate [FM]. When WUS expression highly elevated in the FM, the meristem turn into indeterminate. We showed that WUS activate cytokinine, inhibit auxin response and represses the genes required for root identity fate and that gradual increase in WUCHEL activity leads to gradual meristem enlargement that affect phyllotaxis. We also propose a model in which the direction of WUS domain expansion laterally or upward affects meristem structure differently. We preformed mRNA-seq on meristems with different size and structure followed by k-means clustering and identified groups of genes that are expressed in specific domains at the meristem. We will integrate this data with the ChIP-seq of the 4 TF to add another layer to the genetic network regulating meristem activity.

Age dependent programs are responsible for the physiological and developmental differences of young and mature plants. These include a range of morphological characters such as leaf shape and leaf composition (waxes, lignin etc..) but also different in developmental potentials. Apical buds of juvenile plants are vegetative, while those of mature plants can be reproductive. Likewise, basal buds form in the axills of juvenile leaves have different fates than distal buds formed in the axils of mature leaves. The goal of our joint project is to understand and exploit theses age related programs for specific improvement of crop plants. To that end both the WIS group and the PGEC group are using mutants with age related defects as well as modified expression of miR156 to modify age related programs in crop plants- Tomato and potato in Israel and Maize, switchgrass and Brchipodium in the US. In the US, major effort were made to: Characterize the contribution of selected miR156 target genes to yield component traits of maize. Functional analysis of microRNAs and their targets in new crop plants. In Israel, the research progressed in several directions: Understanding the interplay between age dependent programs and the potential of tomato and potato meristems to produce tubers. Evaluation of the agronomic value of mutants that alter flowering regime in side shoots in general, and in the sympodial buds in particular Characterization of wild type axillary buds, comparing shoot ontogeny of gradually maturing apices from basal and distal positions along the main shoot of tomato.