RESUMO

In higher plants, the shift from vegetative to reproductive development is governed by complex interplay of internal and external signals. TERMINALFLOWER1 (TFL1) plays a crucial role in the regulation of flowering time and inflorescence architecture in Arabidopsis thaliana. This study aimed to explore the function of BdRCN4, a homolog of TFL1 in Brachypodium distachyon, through functional analyses in mutant and transgenic plants. The results revealed that overexpression of BdRCN4 in B. distachyon leads to an extended vegetative phase and reduced production of spikelets. Similar results were found in A. thaliana, where constitutive expression of BdRCN4 promoted a delay in flowering time, followed by the development of hypervegetative shoots, with no flowers or siliques produced. Our results suggest that BdRCN4 acts as a flowering repressor analogous to TFL1, negatively regulating AP1, but no LFY expression. To further validate this hypothesis, a 35S::LFY-GR co-transformation approach on 35::BdRCN4 lines was performed. Remarkably, AP1 expression levels and flower formation were restored to normal in co-transformed plants when treated with dexamethasone. Although further molecular studies will be necessary, the evidence in B. distachyon support the idea that a balance between LFY and BdRCN4/TFL1 seems to be essential for activating AP1 expression and initiating floral organ identity gene expression. This study also demonstrates interesting conservation through the molecular pathways that regulate flowering meristem transition and identity across the evolution of monocot and dicot plants.

Assuntos

RESUMO

KEY MESSAGE: Contrasting morphologies in Disocactus are the result of differential development of the vegetative and floral tissue where intercalary growth is involved, resulting in a complex structure, the floral axis. Species from the Cactaceae bear adaptations related with their growth in environments under hydric stress. These adaptations have translated into the reduction and modification of various structures such as leaves, stems, lateral branches, roots and the structuring of flowers in a so-called flower-shoot. While cacti flowers and fruits have a consistent structure with showy hermaphrodite or unisexual flowers that produce a fruit called cactidium, the developmental dynamics of vegetative and reproductive tissues comprising the reproductive unit have only been inferred through the analysis of pre-anthetic buds. Here we present a comparative analysis of two developmental series covering the early stages of flower formation and organ differentiation in Disocactus speciosus and Disocactus eichlamii, which have contrasting floral morphologies. We observe that within the areole, a shoot apical meristem commences to grow upward, producing lateral leaves with a spiral arrangement, rapidly transitioning to a floral meristem. The floral meristem produces tepal primordia and a staminal ring meristem from which numerous or few stamens develop in a centrifugal manner in D. speciosus and D. eichlamii, respectively. Also, the inferior ovary derives from the floral meristem flattening and an upward growth of the surrounding tissue of the underlying stem, producing the pericarpel. This structure is novel to cacti and lacks a clear anatomical delimitation with the carpel wall. Here, we present a first study that documents the early processes taking place during initial meristem determination related to pericarpel development and early floral organ formation in cacti until the establishment of mature floral organs.

Assuntos

RESUMO

Many developmental processes associated with fruit development occur at the floral meristem (FM). Age-regulated microRNA156 (miR156) and gibberellins (GAs) interact to control flowering time, but their interplay in subsequent stages of reproductive development is poorly understood. Here, in tomato (Solanum lycopersicum), we show that GA and miR156-targeted SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL or SBP) genes interact in the tomato FM and ovary patterning. High GA responses or overexpression of miR156 (156OE), which leads to low expression levels of miR156-silenced SBP genes, resulted in enlarged FMs, ovary indeterminacy and fruits with increased locule number. Conversely, low GA responses reduced indeterminacy and locule number, and overexpression of a S. lycopersicum (Sl)SBP15 allele that is miR156 resistant (rSBP15) reduced FM size and locule number. GA responses were partially required for the defects observed in 156OE and rSBP15 fruits. Transcriptome analysis and genetic interactions revealed shared and divergent functions of miR156-targeted SlSBP genes, PROCERA/DELLA and the classical WUSCHEL/CLAVATA pathway, which has been previously associated with meristem size and determinacy. Our findings reveal that the miR156/SlSBP/GA regulatory module is deployed differently depending on developmental stage and create novel opportunities to fine-tune aspects of fruit development that have been important for tomato domestication.

Assuntos

RESUMO

Angiosperms are the most successful group of land plants. This success is mainly due to the gynoecium, the innermost whorl of the flower. In Arabidopsis, the gynoecium is a syncarpic structure formed by two congenitally fused carpels. At the fusion edges of the carpels, the carpel margin meristem forms. This quasi-meristem is important for medial-tissue development, including the ovules. After the double fertilization, both the seeds and fruit begin to develop. Due to the importance of seeds and fruits as major food sources worldwide, it has been an important task for the scientific community to study gynoecium development. In this review, we present the most recent advances in Arabidopsis gynoecium patterning, as well as some questions that remain unanswered.

Assuntos

RESUMO

Through domestication of wild species, humans have induced large changes in the developmental and circadian clocks of plants. As a result of these changes, modern crops are more productive and adaptive to contrasting environments from the center of origin of their wild ancestors, albeit with low genetic variability and abiotic stress tolerance. Likewise, a complete restructuring of plant metabolic timekeeping probably occurred during crop domestication. Here, we highlight that contrasting timings among organs in wild relatives of crops allowed them to recognize environmental adversities faster. We further propose that connections among biological clocks, which were established during plant domestication, may represent a fundamental source of genetic variation to improve crop resilience and yield.

Assuntos

RESUMO

An in-depth understanding of the development and distribution of laticifer (latex secretory structure) will be important for the production of both rubber and medicines and will support studies on plant adaptations to their environments. We characterize here and describe the ontogenesis of the laticifer sytem in Calotropis procera (Apocynaceae), an invasive subshrub species in arid landscapes. Anatomical and histochemical evaluations of the primary and secondary structures of the stem were carried out on a monthly basis during a full year, with ultrastructural evaluations of laticifer on the stem apex during the rainy season. In the primary structure, laticifer differentiate early from procambium and ground meristem cells of the cortex and medulla and become concentrated adjacent to the external and internal phloem of the bicollateral bundles. In the secondary structure, laticifer differentiates from fusiform derivative cells of the phloem close to the sieve-tube elements. The laticifer is of the articulated, anastomosing, branched type, and it originates from precursor cells that loose the transversal and longitudinal walls by dissolution. Latex is a mixture of terpenes, alkaloids, flavonoids, mucilage, and proteins. The apical meristem and vascular cambium where the laticifer system begins its development are active throughout the year, including during the dry season. The vascular cambium produces phloem with laticifer precursor cells during the rainy season, with high temperatures and long days. The ability of C. procera to grow under water deficit conditions and produce laticifer throughout the year contribute to its wide distribution in arid environments.

Assuntos

RESUMO

MAIN CONCLUSION: Anastomosed laticifers with intrusive growth produce latex containing methyl comate and betulin with economic and ecological value in arid environments. Climatic factors influence laticifer development in the apical meristem and vascular cambium. Latex is a complex emulsion with high medicinal as well as ecological value related to plant survival. Marsdenia zehntneri is a shrubby plant that grows on limestone outcrops in the semiarid regions of Brazil. We sought to characterize the ontogenesis of the laticifers of this species and to relate that process to climatic seasonality and phenology through anatomical, ultrastructural, and micro-morphometric evaluations of the apical meristem and vascular cambium. The histochemistry of the secretory structure was investigated and the chemical composition of the latex was analyzed. Phenological assessments were performed by monitoring phenological events for 1 year. The laticifers network of M. zehntneri permeates the entire primary and secondary body of the plant, providing a wide distribution system of defensive compounds. Its laticifers, of a distinct mixed type (anastomosed, with intrusive growth), are numerous and voluminous in the apical meristem but scarce and minute in the secondary phloem. Latex secretion involves the participation of oleoplasts, polysomes, and dictyosomes. Methyl 2,3-dihydroxy-ursan-23-oate, methyl 3-hydroxy-ursan-23-oate, and betulin are encountered in high proportions in the latex and have ecological and medicinal functions. The development of primary laticifers is related to the resumption of apical meristem activity with increasing day length at the end of the austral winter. The development of secondary laticifers is related to high summer temperatures and rainfall that favor vascular cambium activity. The wide distribution of laticifers, their seasonal pattern of secretion, and their latex composition contribute to the adaptation of M. zehntneri to its natural environment.

Assuntos

RESUMO

Genome-wide association studies (GWAS) have allowed the identification of different loci associated with primary root (PR) growth, and Arabidopsis is an excellent model for these studies. The PR length is controlled by cell proliferation, elongation, and differentiation; however, the specific contribution of proliferation and differentiation in the control of PR growth is still poorly studied. To this end, we analyzed 124 accessions and used a GWAS approach to identify potential causal genomic regions related to four traits: PR length, growth rate, cell proliferation and cell differentiation. Twenty-three genes and five statistically significant SNPs were identified. The SNP with the highest score mapped to the fifth exon of NAC048 and this change makes a missense variant in only 33.3% of the accessions with a large PR, compared with the accessions with a short PR length. Moreover, we detected five more SNPs in this gene and in NAC3 that allow us to discover closely related accessions according to the phylogenetic tree analysis. We also found that the association between genetic variants among the 18 genes with the highest scores in our GWAS and the phenotypic classes into which we divided our accessions are not straightforward and likely follow historical patterns.

RESUMO

A continuum from stem to transit-amplifying to a differentiated cell state is a common theme in multicellular organisms. In the plant root apical meristem (RAM), transit-amplifying cells are organized into two domains: cells from the proliferation domain (PD) are displaced to the transition domain (TD), suggesting that both domains are necessarily coupled. Here, we show that in the Arabidopsis thaliana mto2-2 mutant, in which threonine (Thr) synthesis is affected, the RAM lacks the PD. Through a combination of cell length profile analysis, mathematical modeling and molecular markers, we establish that the PD and TD can be uncoupled. Remarkably, although the RAM of mto2-2 is represented solely by the TD, the known factors of RAM maintenance and auxin signaling are expressed in the mutant. Mathematical modeling predicts that the stem cell niche depends on Thr metabolism and that, when disturbed, the normal continuum of cell states becomes aborted.

Assuntos

RESUMO

Post-embryonic plant development is characterized by a period of vegetative growth during which a combination of intrinsic and extrinsic signals triggers the transition to the reproductive phase. To understand how different flowering inducing and repressing signals are associated with phase transitions of the Shoot Apical Meristem (SAM), we incorporated available data into a dynamic gene regulatory network model for Arabidopsis thaliana. This Flowering Transition Gene Regulatory Network (FT-GRN) formally constitutes a dynamic system-level mechanism based on more than three decades of experimental data on flowering. We provide novel experimental data on the regulatory interactions of one of its twenty-three components: a MADS-box transcription factor XAANTAL2 (XAL2). These data complement the information regarding flowering transition under short days and provides an example of the type of questions that can be addressed by the FT-GRN. The resulting FT-GRN is highly connected and integrates developmental, hormonal, and environmental signals that affect developmental transitions at the SAM. The FT-GRN is a dynamic multi-stable Boolean system, with 223 possible initial states, yet it converges into only 32 attractors. The latter are coherent with the expression profiles of the FT-GRN components that have been experimentally described for the developmental stages of the SAM. Furthermore, the attractors are also highly robust to initial states and to simulated perturbations of the interaction functions. The model recovered the meristem phenotypes of previously described single mutants. We also analyzed the attractors landscape that emerges from the postulated FT-GRN, uncovering which set of signals or components are critical for reproductive competence and the time-order transitions observed in the SAM. Finally, in the context of such GRN, the role of XAL2 under short-day conditions could be understood. Therefore, this model constitutes a robust biological module and the first multi-stable, dynamical systems biology mechanism that integrates the genetic flowering pathways to explain SAM phase transitions.

RESUMO

Colonization of the xylem of sugarcane by Leifsonia xyli subsp. xyli results in the occlusion of the vessels by a gum-like compound and compromises the elongation of the stalk leading to stunted plants. However, no study has been performed in the apical tissue where the elongation of the stalks initiates at the intercalary meristem (IM). Microscopic and histochemical analyses were performed in plants with lower and higher bacterial titers and revealed that in both cases L. xyli subsp. xyli is present in this tissue and colonizes the forming xylem vessels in a similar way as observed in developed internodes. In both cases, it was observed adhering to the secondary walls, but only in plants with higher titers were a mild degradation of the walls and a granular material filling the vessels observed. The mixed composition of lipids, proteins, and pectin indicates that the filling is not a bacterial extracellular polymeric substance. Plants with higher bacterial populations also presented lower starch content in the ground parenchyma at the node elements, possibly resulting from the reported downregulation of photosynthesis and increased accumulation of phenolics. Their second and third IMs presented fewer cells and reduced expression of genes related to the cell cycle and to the synthesis of ABA in the apical tissue. These results indicate that increased L. xyli subsp. xyli colonization affects the development of the IM, which ultimately would reduce the length of the internodes, resulting in the main symptom of the disease.

Assuntos

RESUMO

Passiflora organensis is a small herbaceous vine with characteristic morphological variations throughout its development. The plant bears button-shaped extrafloral nectaries exclusively in adult leaves. Extrafloral nectaries are structures that secrete nectar and play an important role in plant-animal interactions as a strategy for protecting plants against herbivory. In this work, we performed anatomical and ultrastructural studies to characterize P. organensis extrafloral nectaries during their secretory phase. We showed extrafloral nectaries in Passiflora organensis are composed of three distinct regions: nectary epidermis, nectariferous parenchyma, and subnectariferous parenchyma. Our data suggests that all nectary regions constitute a functional unit involved in nectar production and release. The high metabolic activity in the nectary cells is characterized by the juxtaposition of organelles such as mitochondria and plastids together plasmalemma. In addition, calcium oxalate crystals are frequently associated to the nectaries. An increasing concentration of calcium during leaf development and nectary differentiation was observed, corresponding to the calcium deposition as calcium oxalate crystals. This is the first description of extrafloral nectaries in Passiflora organensis that is a promising tropical model species for several studies. RESEARCH HIGHLIGHTS: The anatomical and ultrastructural characteristics and the presence of calcium oxalate crystals in the nectary tissue suggest novel strategies against herbivory in the genus Passiflora.

Assuntos

RESUMO

The objective of this work was to characterize the ontogenesis of Protium spruceanum secretory ducts, to evaluate the effects of seasonality on that process, and to characterize the chemical nature of the resin. Morphometric, anatomical, micromorphometric, histochemical, and ultrastructural evaluations of shoot apexes and chemical analyses of the resin were performed. The ducts of schizolysigenous origin are distributed in the primary and secondary phloem. The subsecretory tissue is meristematic and can restore the secretory epithelium. Secretory epithelial cells have wall thickening resembling that of the Casparian strip that regulates secretion reflux. The main resin compounds are pentacyclic triterpenoids, α- and ß-amyrins, and α- and ß-amyrenones, which are reported here for the first time for this species. The presence of electron-dense and electron-opaque structures, in the secretory epithelial cells, are compatible with the triterpenes and mucilage identified in the resin. Rising temperatures, rainfall, and increasing day length induce the formation of ducts in the vascular cambium throughout Spring/Summer. The abundant production of resin rich in pentacyclic triterpenes indicates the potential use of the species for medicinal and cosmetic purposes. The understanding that secretory processes are concentrated during the Spring/Summer seasons will contribute to the definition of resin extraction management strategies.

RESUMO

KEY MESSAGE: Proper root growth depends on the clearance of TCP transcripts from the root apical meristem by microRNA miR319. The evolutionarily conserved microRNA miR319 regulates genes encoding TCP transcription factors in angiosperms. The miR319-TCP module controls cell proliferation and differentiation in leaves and other aerial organs. The current model sustains that miR319 quantitatively tunes TCP activity during leaf growth and development, ultimately affecting its size. In this work we studied how this module participates in Arabidopsis root development. We found that misregulation of TCP activity through impairment of miR319 binding decreased root meristem size and root length. Cellular and molecular analyses revealed that high TCP activity affects cell number and cyclin expression but not mature cell length, indicating that, in roots, unchecking the expression of miR319-regulated TCPs significantly affects cell proliferation. Conversely, tcp multiple mutants showed no obvious effect on root growth, but strong defects in leaf morphogenesis. Therefore, in contrast to the quantitative regulation of the TCPs by miR319 in leaves, our data suggest that miR319 clears TCP transcripts from root cells. Hence, we provide new insights into the functions of the miR319-TCP regulatory system in Arabidopsis development, highlighting a different modus operandi for its action mechanism in roots and shoots.

Assuntos

RESUMO

Temperature affects plant development therefore phyllochron has been used as a predictor for developmental events to define the time for agricultural managing practices. This study aims to evaluate changes in phyllochron and thermal sum required for flowering by oat genotypes developed at different decades at three temperature regimes; the effect of high temperature on phytomere development; and identify the development stage at the moment of meristem transition to reproductive stage. Three environments were obtained by sowing in the fall, in the spring, and under constant temperature (17ºC), always at inductive photoperiod. Despite changes in nominal values small differences were found among genotypes' phyllochron. Adding specific optimal and maximum temperatures into the growing degree days’ calculation demonstrated phyllochron stability among environments. Plant cycle length and thermal sum correlated with the number of developed phytomeres. UFRGS 078030-2 plants flowered earlier, had a small number of phytomeres, and greater tolerance to elevated temperatures than the other genotypes. More recent genotypes transit to reproductive stage at an earlier Haun stage than older ones.

A temperatura afeta o desenvolvimento das plantas, portanto o filocrono tem sido usado para prever eventos de desenvolvimento e estabelecer o momento adequado para práticas agrícolas. Esse estudo buscou avaliar mudanças em filocrono e soma térmica até o florescimento de genótipos de aveia desenvolvidos em diferentes décadas em três regimes térmicos; o efeito de altas temperaturas no desenvolvimento de fitômeros; e identificar o estágio de desenvolvimento em que ocorre a transição do meristema para a fase reprodutiva. Três ambientes foram estabelecidos pela semeadura no outono, na primavera e em temperatura constante (17ºC), em fotoperíodo indutor. Apesar da alteração dos valores numéricos, houve pouca diferença entre os filocronos dos genótipos. A adição das temperaturas ótima e máxima específicas no cálculo de graus dias demonstrou a estabilidade de filocrono entre ambientes. O ciclo e a soma térmica correlacionaram-se com o número de fitômeros. UFRGS 078030-2 floresceu mais cedo, teve menos fitômeros e maior tolerância a altas temperaturas do que os demais genótipos. Os genótipos mais recentes transitam para a fase reprodutiva em estágios mais precoces da escala Haun, em comparação com os genótipos mais antigos.

Assuntos

RESUMO

Temperature affects plant development therefore phyllochron has been used as a predictor for developmental events to define the time for agricultural managing practices. This study aims to evaluate changes in phyllochron and thermal sum required for flowering by oat genotypes developed at different decades at three temperature regimes; the effect of high temperature on phytomere development; and identify the development stage at the moment of meristem transition to reproductive stage. Three environments were obtained by sowing in the fall, in the spring, and under constant temperature (17ºC), always at inductive photoperiod. Despite changes in nominal values small differences were found among genotypes' phyllochron. Adding specific optimal and maximum temperatures into the growing degree days calculation demonstrated phyllochron stability among environments. Plant cycle length and thermal sum correlated with the number of developed phytomeres. UFRGS 078030-2 plants flowered earlier, had a small number of phytomeres, and greater tolerance to elevated temperatures than the other genotypes. More recent genotypes transit to reproductive stage at an earlier Haun stage than older ones.(AU)

A temperatura afeta o desenvolvimento das plantas, portanto o filocrono tem sido usado para prever eventos de desenvolvimento e estabelecer o momento adequado para práticas agrícolas. Esse estudo buscou avaliar mudanças em filocrono e soma térmica até o florescimento de genótipos de aveia desenvolvidos em diferentes décadas em três regimes térmicos; o efeito de altas temperaturas no desenvolvimento de fitômeros; e identificar o estágio de desenvolvimento em que ocorre a transição do meristema para a fase reprodutiva. Três ambientes foram estabelecidos pela semeadura no outono, na primavera e em temperatura constante (17ºC), em fotoperíodo indutor. Apesar da alteração dos valores numéricos, houve pouca diferença entre os filocronos dos genótipos. A adição das temperaturas ótima e máxima específicas no cálculo de graus dias demonstrou a estabilidade de filocrono entre ambientes. O ciclo e a soma térmica correlacionaram-se com o número de fitômeros. UFRGS 078030-2 floresceu mais cedo, teve menos fitômeros e maior tolerância a altas temperaturas do que os demais genótipos. Os genótipos mais recentes transitam para a fase reprodutiva em estágios mais precoces da escala Haun, em comparação com os genótipos mais antigos.(AU)

Assuntos

RESUMO

ABSTRACT: Temperature affects plant development therefore phyllochron has been used as a predictor for developmental events to define the time for agricultural managing practices. This study aims to evaluate changes in phyllochron and thermal sum required for flowering by oat genotypes developed at different decades at three temperature regimes; the effect of high temperature on phytomere development; and identify the development stage at the moment of meristem transition to reproductive stage. Three environments were obtained by sowing in the fall, in the spring, and under constant temperature (17oC), always at inductive photoperiod. Despite changes in nominal values small differences were found among genotypes' phyllochron. Adding specific optimal and maximum temperatures into the growing degree days' calculation demonstrated phyllochron stability among environments. Plant cycle length and thermal sum correlated with the number of developed phytomeres. UFRGS 078030-2 plants flowered earlier, had a small number of phytomeres, and greater tolerance to elevated temperatures than the other genotypes. More recent genotypes transit to reproductive stage at an earlier Haun stage than older ones.

RESUMO: A temperatura afeta o desenvolvimento das plantas, portanto o filocrono tem sido usado para prever eventos de desenvolvimento e estabelecer o momento adequado para práticas agrícolas. Esse estudo buscou avaliar mudanças em filocrono e soma térmica até o florescimento de genótipos de aveia desenvolvidos em diferentes décadas em três regimes térmicos; o efeito de altas temperaturas no desenvolvimento de fitômeros; e identificar o estágio de desenvolvimento em que ocorre a transição do meristema para a fase reprodutiva. Três ambientes foram estabelecidos pela semeadura no outono, na primavera e em temperatura constante (17oC), em fotoperíodo indutor. Apesar da alteração dos valores numéricos, houve pouca diferença entre os filocronos dos genótipos. A adição das temperaturas ótima e máxima específicas no cálculo de graus dias demonstrou a estabilidade de filocrono entre ambientes. O ciclo e a soma térmica correlacionaram-se com o número de fitômeros. UFRGS 078030-2 floresceu mais cedo, teve menos fitômeros e maior tolerância a altas temperaturas do que os demais genótipos. Os genótipos mais recentes transitam para a fase reprodutiva em estágios mais precoces da escala Haun, em comparação com os genótipos mais antigos.

RESUMO

The anaphase promoting complex/cyclosome (APC/C), a member of the E3 ubiquitin ligase family, plays an important role in recognizing the substrates to be ubiquitylated. Progression of anaphase, and therefore, of the cell cycle, is coordinated through cyclin degradation cycles dependent on proteolysis triggered by APC/C. The APC/C activity depends on the formation of a pocket comprising the catalytic subunits, APC2, APC11, and APC10. Among these, the role of APC11 outside the cell division cycle is poorly understood. Therefore, the goal of this work was to analyze the function of APC11 during plant development by characterizing apc11 knock-down mutant lines. Accordingly, we observed decreased apc11 expression in the mutant lines, followed by a reduction in meristem root size based on the cortical cell length, and an overall size diminishment throughout the development. Additionally, crosses of apc11-1 and amiR-apc11 with plants carrying a WUSCHEL-RELATED HOMEOBOX5 (WOX5) fluorescent marker showed a weakening of the green fluorescent protein-positive cells in the Quiescent Center. Moreover, plants with apc11-1 show a decreased leaf area, together with a decrease in the cell area when the shoot development was observed by kinematics analysis. Finally, we observed a decreased APC/C activity in the root and shoot meristems in crosses of pCYCB1;1:D-box-GUS with apc11-1 plants. Our results indicate that APC11 is important in the early stages of development, mediating meristematic architecture through APC/C activity affecting the overall plant growth.

RESUMO

In multicellular organisms, tissue generation, maintenance, and homeostasis depend on stem cells. Cellular metabolic status is an essential component of different differentiated states, from stem to fully differentiated cells. Threonine (Thr) metabolism has emerged as a critical factor required to maintain pluripotent/multipotent stem cells in both plants and animals. Thus, both kingdoms conserved or converged upon this fundamental feature of stem cell function. Here, we examine similarities and differences in Thr metabolism-dependent mechanisms supporting stem cell maintenance in these two kingdoms. We then consider common features of Thr metabolism in stem cell maintenance and predict and speculate that some knowledge about Thr metabolism and its role in stem cell function in one kingdom may apply to the other. Finally, we outline future research directions to explore these hypotheses.

RESUMO

This special issue is dedicated to the 100th anniversary of the birth of Frederick Albert Lionel Clowes, who discovered the quiescent centre (QC) of the root apical meristem (RAM). His discovery was a foundation for contemporary studies of the QC and RAM function, maintenance, and organization. RAM function is fundamental for cell production and root growth. This special issue bundles reviews on the main tendencies, hypotheses, and future directions, and identifies unknowns in the field.

Assuntos