Vegetative Meristem Research Articles

Modeling phyllotaxis: From the inhibition potential to the real plant

We developed a new parametrization of the classic Douady and Couder model of phyllotaxis based on the inhibition potential: it allowed us to accurately reproduce the vegetative meristem of Linum usitatissimum displaying Fibonacci phyllotaxis, and the reproductive meristem of Ranunculus repens. We calculated the inhibition potential within the meristem and the auxin concentration at the front. We show that phyllotaxis modes and the convergence of the divergence angles towards “noble” angles are the consequence of minimizing the inhibitory potential under the constraint of decreasing plastochron ratios. Our approach, which gives a physicochemical basis to the van Iterson diagram, produces the same results as approaches based on mechanical constraints, suggesting these are two facets of the same botanical reality.

Over-Expression of Larch DAL1 Accelerates Life-Cycle Progression in Arabidopsis

Homologs of Larix kaempferiDEFICIENS-AGAMOUS-LIKE 1 (LaDAL1) promote flowering in Arabidopsis. However, their functional role in the whole life-cycle is limited. Here, we analyzed the phenotypes and transcriptomes of Arabidopsis plants over-expressing LaDAL1. With respect to the defined life-cycle stage of Arabidopsis based on the meristem state, the results showed that LaDAL1 promoted seed germination, bolting, flower initiation, and global proliferative arrest, indicating that LaDAL1 accelerates the meristem reactivation, the transitions of vegetative meristem to inflorescence and flower meristem, and meristem arrest. As a marker gene of meristem, TERMINAL FLOWER 1 was down-regulated after LaDAL1 over-expression. These results reveal that LaDAL1 accelerates the life-cycle progression in Arabidopsis by promoting the transition of meristem fate, providing more and novel functional information about the conifer age-related gene DAL1.

Natural Variation in the Control of Flowering and Shoot Architecture in Diploid Fragaria Species.

In perennial fruit and berry crops of the Rosaceae family, flower initiation occurs in late summer or autumn after downregulation of a strong repressor TERMINAL FLOWER1 (TFL1), and flowering and fruiting takes place the following growing season. Rosaceous fruit trees typically form two types of axillary shoots, short flower-bearing shoots called spurs and long shoots that are, respectively, analogous to branch crowns and stolons in strawberry. However, regulation of flowering and shoot architecture differs between species, and environmental and endogenous controlling mechanisms have just started to emerge. In woodland strawberry (Fragaria vesca L.), long days maintain vegetative meristems and promote stolon formation by activating TFL1 and GIBBERELLIN 20-OXIDASE4 (GA20ox4), respectively, while silencing of these factors by short days and cool temperatures induces flowering and branch crown formation. We characterized flowering responses of 14 accessions of seven diploid Fragaria species native to diverse habitats in the northern hemisphere and selected two species with contrasting environmental responses, Fragaria bucharica Losinsk. and Fragaria nilgerrensis Schlecht. ex J. Gay for detailed studies together with Fragaria vesca. Similar to F. vesca, short days at 18°C promoted flowering in F. bucharica, and the species was induced to flower regardless of photoperiod at 11°C after silencing of TFL1. F. nilgerrensis maintained higher TFL1 expression level and likely required cooler temperatures or longer exposure to inductive treatments to flower. We also found that high expression of GA20ox4 was associated with stolon formation in all three species, and its downregulation by short days and cool temperature coincided with branch crown formation in F. vesca and F. nilgerrensis, although the latter did not flower. F. bucharica, in contrast, rarely formed branch crowns, regardless of flowering or GA20ox4 expression level. Our findings highlighted diploid Fragaria species as rich sources of genetic variation controlling flowering and plant architecture, with potential applications in breeding of Rosaceous crops.

Untangling inflorescences in Miconieae (Melastomataceae): development, typology, and the systematic and evolutionary implications.

This study aimed to describe the origin, position, development and typology of inflorescences in Miconieae through ontogenetic and morphological analyses using light microscopy. We observed three morphological character states: terminal, pseudo-axillary and axillary; and two ontogenetic states: terminal and axillary. The terminal and pseudoaxillary inflorescences originate from terminal reproductive meristems. Pseudoaxillary inflorescences result from unequal development of vegetative meristems which flank the terminal flowering unit, whereas in terminal inflorescences, both vegetative meristems develop equally. In axillary inflorescences, the terminal reproductive meristem is not involved, while axillary inflorescences originate from reproductive axillary meristems. The inflorescences range from heterocladic and thyrsoid to simpler types, such as botryoid and triad. Such characteristics can also be seen in paracladia, particularly those most distal. The terminal inflorescence is observed in all clades of Miconieae, and pseudoaxillary and axillary inflorescences should be apomorphic states in the tribe and derived from the terminal condition.

Secretory Patterns in Colleters of Apocynaceae.

Colleters of Apocynaceae are glands related to different types of protection of vegetative and floral meristems through the production of mucilage or a mixture of many different compounds. Although several anatomical papers have shown histological and histochemical aspects of colleters of the family, almost nothing is known about their secretory process. In this study, we analyzed two types of colleters in Apocynaceae: one produces mucilage and lipophilic compounds, while the other produces an exclusively mucilaginous secretion. The secretory epidermis of the colleters of Allamanda schottii and Blepharodon bicuspidatum has a dense cytoplasm with organelles responsible for the production of mucilage and lipids. This heterogeneous secretion is released through granulocrine and eccrine mechanisms and is temporarily stored in a subcuticular space before crossing the cuticle. Conversely, colleters of Mandevilla splendens and Peplonia axillaris produce only mucilage and have a very different secretory apparatus. The mechanism of secretion is granulocrine, and the exudate is firstly accumulated in a large periplasmic space and later in an intramural space before crossing the cuticle. Notably, the structure of the cuticle varies according to the secretion composition. Although the colleters of the family are histologically similar, this study demonstrates a metabolic and subcellular variability previously unknown for Apocynaceae.

Genome-Wide Analysis of the MADS-Box Gene Family in Maize: Gene Structure, Evolution, and Relationships.

The MADS-box gene family is one of the largest families in plants and plays an important roles in floral development. The MADS-box family includes the SRF-like domain and K-box domain. It is considered that the MADS-box gene family encodes a DNA-binding domain that is generally related to transcription factors, and plays important roles in regulating floral development. Our study identified 211 MADS-box protein sequences in the Zea mays proteome and renamed all the genes based on the gene annotations. All the 211 MADS-box protein sequences were coded by 98 expressed genes. Phylogenetic analysis of the MADS-box genes showed that all the family members were categorized into five subfamilies: MIKC-type, Mα, Mβ, Mγ, and Mδ. Gene duplications are regarded as products of several types of errors during the period of DNA replication and reconstruction; in our study all the 98 MADS-box genes contained 22 pairs of segmentally duplicated events which were distributed on 10 chromosomes. We compared expression data in different tissues from the female spikelet, silk, pericarp aleurone, ear primordium, leaf zone, vegetative meristem, internode, endosperm crown, mature pollen, embryo, root cortex, secondary root, germination kernels, primary root, root elongation zone, and root meristem. According to analysis of gene ontology pathways, we found a total of 41 pathways in which MADS-box genes in maize are involved. All the studies we conducted provided an overview of MADS-box gene family members in maize and showed multiple functions as transcription factors. The related research of MADS-box domains has provided the theoretical basis of MADS-box domains for agricultural applications.

Evolution and expression of the MADS-box flowering transition genes AGAMOUS-like 24/SHORT VEGETATIVE PHASE with emphasis in selected Neotropical orchids.

In angiosperms the reproductive transition results in the transformation of a vegetative apical meristem (SAM) into an inflorescence meristem (IM), capable of forming floral meristems (FM). Two key players in the flowering transition are AGAMOUS-like 24 (AGL24) and SHORT VEGETATIVE PHASE (SVP). They are eudicot MADS-box paralogs performing opposite roles, as AGL24 positively regulates flowering while SVP represses the reproductive transition in Arabidopsis. We confirm that the Arabidopsis functional reference cannot be readily extrapolated to all eudicots as there are additional duplications of AGL24 in early divergent eudicots and core eudicots with significant sequence variation. In addition, we found that in monocots, two additional independent duplication events have resulted in at least three clades of AGL24/SVP homologs, some only found in Orchidaceae. Protein sequence analyses and comparative evolutionary rates point to higher rates of relaxed negative selection in the Core Eudicot AGL24 B and the Orch SVP-like B clades, in eudicots and monocots respectively. On the other hand, expression data points to plesiomorphic pleiotropic roles of AGL24/SVP genes likely similar to SVP core eudicot genes, and the acquisition of new roles as flowering positive regulators in Core Eudicot AGL24 A genes. Our research presents evidence on the diversification and recruitment of AGL24/SVP homologs in flowering transition in orchids. Although, broad expression of most copies does not allow to determine if they act as flowering repressors or promoters, the restricted expression of some homologs in the SAM suggests putative roles in maintaining the vegetative phase. If so studying in detail the function of AGL24/SVP homologs in orchids is critical to identify putative flowering repressors in a lineage where other canonical repressors remain elusive.

RNAi Suppression of LEAFY Gives Stable Floral Sterility, and Reduced Growth Rate and Leaf Size, in Field-Grown Poplars

The central floral development gene LEAFY (LFY), whose mutation leads to striking changes in flowering and often sterility, is commonly expressed in non-floral structures; however, its role in vegetative development is poorly understood. Sterility associated with suppression of LFY expression is an attractive means for mitigating gene flow by both seeds and pollen in vegetatively propagated forest trees, but the consequences of its suppression for tree form and wood production are unclear. To study the vegetative effects of RNAi suppression of LFY, we created a randomized, multiple-year field study with 30–40 trees (ramets) in each of two sterile gene insertion events, three transgenic control events, and a wild-type control population. We found that floral knock-down phenotypes were stable across years and propagation cycles, but that several leaf morphology and productivity traits were statistically and often substantially different in sterile vs. normal flowering RNAi-LFY trees. Though trees with suppressed LEAFY expression looked visibly normal, they appear to have reduced growth and altered leaf traits. LFY appears to have a significant role in vegetative meristem development, and evaluation of vegetative impacts from LFY suppression would be prudent prior to large-scale use for genetic containment.

Molecular Insights into Inflorescence Meristem Specification for Yield Potential in Cereal Crops.

Flowering plants develop new organs throughout their life cycle. The vegetative shoot apical meristem (SAM) generates leaf whorls, branches and stems, whereas the reproductive SAM, called the inflorescence meristem (IM), forms florets arranged on a stem or an axis. In cereal crops, the inflorescence producing grains from fertilized florets makes the major yield contribution, which is determined by the numbers and structures of branches, spikelets and florets within the inflorescence. The developmental progression largely depends on the activity of IM. The proper regulations of IM size, specification and termination are outcomes of complex interactions between promoting and restricting factors/signals. Here, we focus on recent advances in molecular mechanisms underlying potential pathways of IM identification, maintenance and differentiation in cereal crops, including rice (Oryza sativa), maize (Zea mays), wheat (Triticum aestivum), and barley (Hordeum vulgare), highlighting the researches that have facilitated grain yield by, for example, modifying the number of inflorescence branches. Combinatorial functions of key regulators and crosstalk in IM determinacy and specification are summarized. This review delivers the knowledge to crop breeding applications aiming to the improvements in yield performance and productivity.

CENTRORADIALIS maintains shoot meristem indeterminacy by antagonizing THORN IDENTITY1 in Citrus

Differential regulation of stem cell activity in shoot meristems contributes to the wide variation in shoot architecture.1-3 In most Citrus species, a thorn meristem and a dormant axillary meristem co-localize at each leaf base, offset from each other in a spiral phyllotactic pattern. We recently identified THORN IDENTITY1 (TI1) and THORN IDENTITY2 (TI2), encoding TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) transcription factors, as necessary for the termination of meristem proliferation and concomitant thorn production in Citrus.4 However, how the dormant axillary meristem at the same leaf axil maintains stem cell activity is still unknown. The phosphatidylethanolamine-binding protein (PEBP)-type transcription factors CENTRORADIALIS (CEN) and TERMINAL FLOWER1 (TFL1) maintain inflorescence meristem indeterminacy in many plant species by antagonizing floral meristem identity regulators.5-9 Here, we show that, in Citrus, Citrus CEN (CsCEN) maintains vegetative axillary meristem indeterminacy by antagonizing TI1. CsCEN is expressed in the axillary meristem, but not in the thorn meristem. Disruption of CsCEN function results in termination of the stem cell activity and conversion of dormant axillary meristems into thorns, although ectopic overexpression of CsCEN represses TI1 expression and converts thorns into dormant buds, a phenotype similar to the ti1 mutant. We further show that CsCEN interacts with Citrus FD (CsFD) to repress TI1 expression. CsCEN activity depends on the function of TI1 and TI2, as mutations in TI1 and TI2 rescue the cscen mutant phenotype. We suggest that the antagonistic roles of CsCEN and TI1 define the pattern of axillary meristem determinacy, which shapes vegetative Citrus tree shoot architecture.

Changes of Growth and Inflorescence Initiation by Exogenous Gibberellic Acid3 and 6-Benzylaminopurine Application in Phalaenopsis Orchids

This study was conducted to observe the effects of exogenous gibberellic acid3 (GA3) and 6-benzylaminopurine (BAP) treatments on the growth and inflorescence initiation of Phalaenopsis and to determine whether hormonal applications can substitute for low-temperature exposure for floral transition. Phalaenopsis Queen Beer ‘Mantefon’ clones were treated with no hormones (control), GA3 100 mg/L, GA3 200 mg/L, BAP 100 mg/L, and GA3 100 mg/L + BAP 100 mg/L by foliar spray. The treatments were carried at 28 °C for vegetative growth and 20 °C for forcing, respectively. At 28 °C of vegetative temperature, all exogenous hormonal treatments did not induce inflorescence initiation, but lateral shoots were observed in BAP-treated plants even though this plant is a monopodial orchid. GA3 significantly increased leaf length and decreased leaf width, and consequently increased length:width (L:W) ratio compared with the control and BAP alone. The trend grew as GA3 concentration increased. Also, the GA3 increased stem length and decreased stem diameter. At 20 °C of forcing temperature, L:W ratio responded similarly to 28 °C in GA3 treatments, but leaf size was smaller than for the control or BAP alone. BAP accelerated inflorescence emergence and significantly increased inflorescence numbers, whereas GA3 and GA3 + BAP slightly delayed inflorescence emergence. GA3 significantly promoted new leaf development at 20 °C of forcing condition. These results indicated that cytokinin was associated with the break of axillary vegetative and inflorescence meristems and exogenous GA3 spray did not improve inflorescence initiation in Phalaenopsis. Although exogenous hormonal application did not substitute for low-temperature exposure, it showed a possibility in promoting the growth and inflorescence initiation.

An overview of the endogenous and environmental factors related to the <i>Coffea arabica</i> flowering process

The transition of vegetative meristems to a reproductive state followed by floral development and flowering is a complex process regulated by many regulatory pathways that integrate (epi) genetic and environmental factors to guarantee the reproductive success in angiosperms. In woody and perennial species, such as coffee trees, the extended life cycle reflects adaptive strategies, i.e., two-year cycle, sequential flowering and bud latency during the winter, that ensure reproductive success in a variable environment. The dynamics of coffee flowering integrate multiple stimuli to induce morpho-physiological changes, especially during the reproductive phase. We discussed diverse stimuli which are directly and indirectly associated with molecular pathways related to the reproductive meristem transition and floral development until anthesis. Here, we propose to redefine some concepts regarding coffee floral development, such as: i) A summary of genes possibly involved in the flowering pathways; ii) A new classification of buds by position in the node (B1 - B4) to avoid misunderstandings with the uneven developmental stages; iii) comparative ABC model to <i>Arabidopsis</i> and tomato to allow evolutionary discussions of whorls development in <i>Coffea</i> sp. From this, we expect to collaborate to drive future studies towards coffee breeding and production, for example, improving floral buds activation, controlling the flowering time, anthesis synchronization to produce more homogeneous ripening fruits, reducing abortion or early flower openings, and increasing fruitification. Moreover, we think that the explored relationship between physiological and molecular approaches during the coffee flowering may be extended to understand other tropical perennial species, especially those with asynchronous flowering behavior, and to understand evolutive aspects in <i>Rubiaceae.</i>

Live Imaging of Arabidopsis Leaf and Vegetative Meristem Development.

Plants develop lateral organs such as leaves and flowers throughout their post-embryonic life from a structure called the shoot apical meristem (SAM), located at the plant shoot apex. This process is highly dynamic, and therefore in order to understand meristem and organ development, it is critical to be able to analyze these processes with high temporal and spatial resolution. Although several protocols have been published for imaging the Arabidopsis inflorescence meristem, gaining access to the vegetative meristem for imaging has been considered more difficult. Here we describe a method to dissect young Arabidopsis seedlings in order to obtain a clear view of the vegetative meristem and young leaf primordia using confocal microscopy.

From Embryo to Adult: Low Temperatures Affect Phase Transitions of Allium sativum L. from Germination to Flowering

Juvenile and vegetative adult shoot apical meristems (SAM) are actively involved in acquisition of flowering competence, while the embryonic SAM is regarded as “responsible” only for germination. Comparative analyses of imbibed and stratified seeds of garlic Allium sativum show that only stratified seedlings produced bulbs and flower stems at the end of the season. Since the seed morphology of stratified and non-stratified seeds prior to sowing was similar, the differences are attributed to the molecular alterations in the embryonic SAM. Functional annotation analysis of 3000 differentially expressed genes suggests that seed imbibition reactivates the embryonic cell cycle, initiates the metabolism, and primes garlic seed germination. Stratification enhances DNA modifications, biosynthesis, cellular transport, and tissue development. Similar to vernalization of the vegetative buds, stratification of the embryonic SAM resulted in altered expression of meristem-identity and flowering homologs. Phase transitions from seed germination to flowering and bulbing in A. sativum are tightly connected, and possibly associated with downregulation of specific flowering repressor(s). The embryonic SAM plays an important role not only in seed germination, but in the entire plant life cycle, providing the foundation for the genetic regulation of major functional shifts in metabolism and development.

Root and axillary shoot development of hairy vetch stem cuttings and cessation of flower development under a short photoperiod

AbstractClonal propagation is a valuable tool for plant breeders to maintain heterozygous genotypes in crop species that are not amenable to self‐pollination or apomixis. An example is the drought‐tolerant forage and N‐fixing cover crop hairy vetch (Vicia villosa Roth), which primarily outcrosses and is developed into composite cultivars by plant breeders. The ability to obtain clones of desirable genotypes in breeding nurseries would enable the maintenance of heterozygous genotypes for genetic study or the ability to reconstitute a true synthetic cultivar. We developed an efficient method of clonal propagation from stem cuttings to maintain genotypes in a vegetative state for a minimum of 2 yr, even when obtained from flowering parental plants. The long‐term viability of such clones is unknown, however. We determined that hairy vetch, which flowers under long days, exhibits a form of partial flowering where vegetative meristems are maintained during conditions that induce flowering. Clones obtained from flowering parents would resume reproductive growth and eventually senesce if kept in inductive conditions. However, if clones were grown under a continuous 6‐h photoperiod, reproductive development would cease and vegetative growth would resume indefinitely.

Meristem Genes in the Highly Reduced Endoparasitic Pilostyles boyacensis (Apodanthaceae)

The family Apodanthaceae comprises two genera (Apodanthes and Pilostyles) and 14 endoparasitic species, all of them lacking root and shoot apical meristems, stems and leaves. Their vegetative phase is reduced to a mycelium-like endophyte formed by strands of parenchyma cells that are in close contact to the host vasculature. These plants become apparent only when their tiny gregarious flowers emerge breaking through the host cortex. The lack of vegetative meristems in these plants sharply contrasts to the typical formation of floral meristems. Our target species, Pilostyles boyacensis, provides a suitable system to investigate the evolution of meristem –related genes in an endoparasitic flowering plant without a typical vegetative shoot apical meristem. We have generated transcriptomes from two different developmental stages of the parasite (emerged floral buds and fruits), as well as a mixed sample that comprises the endophyte and growing floral buds of the parasite and its host, Dalea cuatrecasasii (Fabaceae). We specifically assessed copy number and domain conservation for the WUSCHEL HOMEOBOX, LRR-RLK-IX-a, and CLE families related to the maintenance of the shoot apical meristem (SAM) as well as the ARF and LFY families responsible for floral meristem identity. Five out of the 11 canonical gene families responsible for SAM maintenance and floral fate determinacy targeted in this study were found in Pilostyles. P. boyacensis shows at least one transcript with all functional domains conserved for BAM1, WUS, WOX9, ARF7 and LFY. Other genes implicated in the canonical regulatory network could not be found, including ARF5, ARF19, BAM2, BAM3, CLV1, and CLV3. In conclusion, the endoparasitic lifestyle of Apodanthaceae appears to correlate with a substantial reduction in the transcriptomic machinery linked to SAMs, whereas the genes involved in flower fate have remained intact.

Molecular oxygen as a signaling component in plant development.

While traditionally hypoxia has been studied as a detrimental component of flooding stress, the last decade has flourished with studies reporting the involvement of molecular oxygen availability in plant developmental processes. Moreover, proliferating and undifferentiated cells from different plant tissues were found to reside in endogenously generated hypoxic niches. Thus, stress-associated acute hypoxia may be distinguished from constitutively generated chronic hypoxia. The Cys/Arg branch of the N-degron pathway assumes a central role in integrating oxygen levels resulting in proteolysis of transcriptional regulators that control different aspects of plant growth and development. As a target of this pathway, group VII of the Ethylene Response Factor (ERF-VII) family has emerged as a hub for the integration of oxygen dynamics in root development and during seedling establishment. Additionally, vegetative shoot meristem activity and reproductive transition were recently associated with oxygen availability via two novel substrates of the N-degron pathways: VERNALISATION 2 (VRN2) and LITTLE ZIPPER 2 (ZPR2). Together, these observations support roles for molecular oxygen as a signalling molecule in plant development, as well as in essential metabolic reactions. Here, we review recent findings regarding oxygen-regulated development, and discuss outstanding questions that spring from these discoveries.

Cloning and functional characterization of a floral repressor gene from Lavandula angustifolia.

Using RNA-Seq, we identified genes involved in floral development in lavenders and functionally characterized the floral repressor LaSVP. The molecular aspects of flower initiation and development have not been adequately investigated in lavender (Lavandula). In order to identify genes that control these processes, we employed RNA-Seq to obtain sequence information for transcripts originating from the vegetative shoot apical meristem (SAM) and developing inflorescence tissues of Lavandula angustifolia and Lavandula × intermedia plants, and assemble a comprehensive transcriptome of 105,294 contigs. Homology-based annotation provided gene ontology terms for the majority of transcripts, including over 100 genes homologous to those that control flower initiation and organ identity in Arabidopsis thaliana. Expression analysis revealed that most of these genes are differentially expressed during flower development. For example, LaSVP, a homolog of the floral repressor SHORT VEGETATIVE PHASE (SVP), was strongly expressed in vegetative SAM compared to developing flowers, implicating its potential involvement in flowering repression in lavender. To investigate LaSVP further, we constitutively expressed the gene in transformed A. thaliana plants, evaluating its effects on flower initiation and morphology. Expression of theLaSVP in A. thaliana delayed flowering and affected flower organ identity in a dosage-dependent manner. Two of the highest expressing lines produced sepals instead of petals and were sterile as they failed to develop proper seed pods. This study provides the foundation for future investigations aimed at elucidating flower initiation and development in lavender.

Genetic and Reproductive State Assessment of Ulmus pumila and U. suberosa Invasive Populations in the Dnieper Steppe under Climate Change

The degree of intraspecific genetic polymorphism and heterozygosity, the germinal death, viability of seeds, and the cytogenetic state of vegetative Ulmus pumila and U. suberosa meristems were analyzed for determining the mechanisms of plant population invasiveness in the steppe Dnieper region under climate changes. The studied U. pumila population were different in terms of germinal (embryonic) death, seed viability and seed productivity. Populations grown under more favorable environmental conditions had the best reproductive, physiological and genetic conditions. For the majority of used microsatellite loci, population studies were characterized by a relatively low level of genetic variability, an excess of homozygous genotypes and a deficiency of heterozygotes, which indicated a certain level of inbreeding of the analyzed plants. The highest deficiency of heterozygotes was found in U. pumila populations with high stand density and significant indices of germinal seed loss; smaller deficits were in populations with a larger area and low stand density and, accordingly, low rates of germinal death. The low index of chromosomal rearrangements in the vegetative meristems also confirmed an insignificant level of genetic variability and the probable absence of hybridization and genetic homeostasis in U. pumila. The U. suberosa population was characterized by increased indices of germinal death, seed damage and low seed productivity, which correlated with an excess of homozygous genotypes. All U. suberosa specimens were monomorphic by the microsatellite loci. In general, by genetic and reproductive indices, seed reproduction and distribution of U. pumila in the steppe Dnieper region is not significantly limited under climate change. At the same time, seed reproduction of U. suberosa may be limited.

Inflorescence Meristem Fate Is Dependent on Seed Development and FRUITFULL in Arabidopsis thaliana.

After a vegetative phase, plants initiate the floral transition in response to both environmental and endogenous cues to optimize reproductive success. During this process, the vegetative shoot apical meristem (SAM), which was producing leaves and branches, becomes an inflorescence SAM and starts producing flowers. Inflorescences can be classified in two main categories, depending on the fate of the inflorescence meristem: determinate or indeterminate. In determinate inflorescences, the SAM differentiates directly, or after the production of a certain number of flowers, into a flower, while in indeterminate inflorescences the SAM remains indeterminate and produces continuously new flowers. Even though indeterminate inflorescences have an undifferentiated SAM, the number of flowers produced by a plant is not indefinite and is characteristic of each species, indicating that it is under genetic control. In Arabidopsis thaliana and other species with indeterminate inflorescences, the end of flower production occurs by a regulated proliferative arrest of inflorescence meristems on all reproductive branches that is reminiscent of a state of induced dormancy and does not involve the determination of the SAM. This process is controlled genetically by the FRUITFULL-APETALA2 (FUL-AP2) pathway and by a correlative control exerted by the seeds through a mechanism not well understood yet. In the absence of seeds, meristem proliferative arrest does not occur, and the SAM remains actively producing flowers until it becomes determinate, differentiating into a terminal floral structure. Here we show that the indeterminate growth habit of Arabidopsis inflorescences is a facultative condition imposed by the meristematic arrest directed by FUL and the correlative signal of seeds. The terminal differentiation of the SAM when seed production is absent correlates with the induction of AGAMOUS expression in the SAM. Moreover, terminal flower formation is strictly dependent on the activity of FUL, as it was never observed in ful mutants, regardless of the fertility of the plant or the presence/absence of the AG repression exerted by APETALA2 related factors.