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Phosphorus (P) is an essential macronutrient for maize (Zea mays L.) growth and development. Therefore, generating cultivars with upgraded P use efficiency (PUE) represents one of the main strategies to reduce the global agriculture dependence on phosphate fertilizers. In this work, genome-wide association studies (GWAS) were performed to detect quantitative trait nucleotide (QTN) and potential PUE-related candidate genes and associated traits in greenhouse and field trials under contrasting P conditions. The PUE and other agronomy traits of 132 maize inbred lines were assessed in low and normal P supply through the greenhouse and field experiments and Multi-locus GWAS was used to map the associated QTNs. Wide genetic variability was observed among the maize inbred lines under low and normal P supply. In addition, we confirm the complex and quantitative nature of PUE. A total of 306 QTNs were associated with the 24 traits evaluated using different multi-locus GWAS methods. A total of 186 potential candidate genes were identified, mainly involved with transcription regulator, transporter, and transference activity. Further studies are still needed to elucidate the functions and relevance of these genes regarding PUE. Nevertheless, pyramiding the favorable alleles pinpointed in the present study can be considered an efficient strategy for molecular improvement to increase maize PUE.
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BACKGROUND: On tropical regions, phosphorus (P) fixation onto aluminum and iron oxides in soil clays restricts P diffusion from the soil to the root surface, limiting crop yields. While increased root surface area favors P uptake under low-P availability, the relationship between the three-dimensional arrangement of the root system and P efficiency remains elusive. Here, we simultaneously assessed allelic effects of loci associated with a variety of root and P efficiency traits, in addition to grain yield under low-P availability, using multi-trait genome-wide association. We also set out to establish the relationship between root architectural traits assessed in hydroponics and in a low-P soil. Our goal was to better understand the influence of root morphology and architecture in sorghum performance under low-P availability. RESULT: In general, the same alleles of associated SNPs increased root and P efficiency traits including grain yield in a low-P soil. We found that sorghum P efficiency relies on pleiotropic loci affecting root traits, which enhance grain yield under low-P availability. Root systems with enhanced surface area stemming from lateral root proliferation mostly up to 40 cm soil depth are important for sorghum adaptation to low-P soils, indicating that differences in root morphology leading to enhanced P uptake occur exactly in the soil layer where P is found at the highest concentration. CONCLUSION: Integrated QTLs detected in different mapping populations now provide a comprehensive molecular genetic framework for P efficiency studies in sorghum. This indicated extensive conservation of P efficiency QTL across populations and emphasized the terminal portion of chromosome 3 as an important region for P efficiency in sorghum. Increases in root surface area via enhancement of lateral root development is a relevant trait for sorghum low-P soil adaptation, impacting the overall architecture of the sorghum root system. In turn, particularly concerning the critical trait for water and nutrient uptake, root surface area, root system development in deeper soil layers does not occur at the expense of shallow rooting, which may be a key reason leading to the distinctive sorghum adaptation to tropical soils with multiple abiotic stresses including low P availability and drought.
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Estudio de Asociación del Genoma Completo , Fósforo , Raíces de Plantas , Sitios de Carácter Cuantitativo , Sorghum , Sorghum/genética , Sorghum/metabolismo , Sorghum/crecimiento & desarrollo , Fósforo/metabolismo , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Raíces de Plantas/genética , Raíces de Plantas/anatomía & histología , Mapeo Cromosómico , Polimorfismo de Nucleótido Simple , Suelo/química , FenotipoRESUMEN
Legume plants develop two types of root postembryonic organs, lateral roots and symbiotic nodules, using shared regulatory components. The module composed by the microRNA390, the Trans-Acting SIRNA3 (TAS3) RNA and the Auxin Response Factors (ARF)2, ARF3, and ARF4 (miR390/TAS3/ARFs) mediates the control of both lateral roots and symbiotic nodules in legumes. Here, a transcriptomic approach identified a member of the Lateral Organ Boundaries Domain (LBD) family of transcription factors in Medicago truncatula, designated MtLBD17/29a, which is regulated by the miR390/TAS3/ARFs module. ChIP-PCR experiments evidenced that MtARF2 binds to an Auxin Response Element present in the MtLBD17/29a promoter. MtLBD17/29a is expressed in root meristems, lateral root primordia, and noninfected cells of symbiotic nodules. Knockdown of MtLBD17/29a reduced the length of primary and lateral roots and enhanced lateral root formation, whereas overexpression of MtLBD17/29a produced the opposite phenotype. Interestingly, both knockdown and overexpression of MtLBD17/29a reduced nodule number and infection events and impaired the induction of the symbiotic genes Nodulation Signaling Pathway (NSP) 1 and 2. Our results demonstrate that MtLBD17/29a is regulated by the miR390/TAS3/ARFs module and a direct target of MtARF2, revealing a new lateral root regulatory hub recruited by legumes to act in the root nodule symbiotic program.
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Medicago truncatula , Proteínas de Plantas , Nodulación de la Raíz de la Planta , Raíces de Plantas , Factores de Transcripción , Regulación de la Expresión Génica de las Plantas , Técnicas de Silenciamiento del Gen , Ácidos Indolacéticos/metabolismo , Medicago truncatula/genética , Medicago truncatula/crecimiento & desarrollo , Medicago truncatula/microbiología , MicroARNs/genética , MicroARNs/metabolismo , Proteínas de Plantas/metabolismo , Proteínas de Plantas/genética , Nodulación de la Raíz de la Planta/genética , Raíces de Plantas/genética , Raíces de Plantas/crecimiento & desarrollo , Regiones Promotoras Genéticas/genética , Nódulos de las Raíces de las Plantas/genética , Nódulos de las Raíces de las Plantas/crecimiento & desarrollo , Simbiosis/genética , Factores de Transcripción/metabolismo , Factores de Transcripción/genéticaRESUMEN
Soil alkalinity is a critical environmental factor for plant growth and distribution in ecosystems. An alkaline condition (pH > 7) is imposed by the rising concentration of hydroxides and cations, and prevails in semiarid and arid environments, which represent more than 25% of the total arable land of the world. Despite the great pressure exerted by alkalinity for root viability and plant survival, scarce information is available to understand how root microbes contribute to alkaline pH adaptation. Here, we assessed the effects of alkalinity on shoot and root biomass production, chlorophyll content, root growth and branching, lateral root primordia formation, and the expression of CYCB1, TOR kinase, and auxin and cytokinin-inducible trangenes in shoots and roots of Arabidopsis seedlings grown in Petri plates with agar-nutrient medium at pH values of 7.0, 7.5, 8.0, 8.5, and 9.0. The results showed an inverse correlation between the rise of pH and most growth, hormonal and genetic traits analyzed. Noteworthy, root inoculation with Achromobacter sp. 5B1, a beneficial rhizospheric bacterium, with plant growth promoting and salt tolerance features, increased biomass production, restored root growth and branching and enhanced auxin responses in WT seedlings and auxin-related mutants aux1-7 and eir1, indicating that stress adaptation operates independently of canonical auxin transporter proteins. Sequencing of the Achromobacter sp. 5B1 genome unveiled 5244 protein-coding genes, including genes possibly involved in auxin biosynthesis, quorum-sensing regulation and stress adaptation, which may account for its plant growth promotion attributes. These data highlight the critical role of rhizobacteria to increase plant resilience under high soil pH conditions potentially through genes for adaptation to an extreme environment and bacteria-plant communication.
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Proteínas de Arabidopsis , Arabidopsis , Plantones , Proteínas de Arabidopsis/genética , Ecosistema , Raíces de Plantas , Ácidos Indolacéticos/metabolismo , Suelo , Regulación de la Expresión Génica de las PlantasRESUMEN
Although most cultivated soils have high levels of total phosphorus (P), the levels of bioavailable inorganic P (Pi) are insufficient. The application of plant-growth-promoting rhizobacteria (PGPR) is an eco-friendly strategy for P utilization; however, PGPR-mediated plant responses that enhance Pi acquisition remain unexplored. Here, we investigated the effect of Azospirillum brasilense on Arabidopsis adaptation to Pi deficiency. Results showed that A. brasilense inoculation alleviated Pi-deficiency-induced growth inhibition and anthocyanin accumulation and increased the total P content in Arabidopsis plants. A comprehensive analysis of root morphology revealed that A. brasilense increased root hair density and length under Pi-limited conditions. We further demonstrated that A. brasilense enhanced the acid phosphatase activity and upregulated the expression of several Pi transporter genes, such as PHOSPHATE1 (PHO1), PHOSPHATE TRANSPORTER 1:(PHT1:1) and PHT1;4. However, A. brasilense did not enhance the growth o total P content in pht1;1, pht1;4 and pht1;1pht1;4 mutants. Moreover, A. brasilense could not increase the P content and PHT1;1 expression in the root hairless mutant rsl4rsl2, because of the occurrence of low-Pi-induced PHT1;1 and PHT1;4 in root hairs. These results indicate that A. brasilense can promote root hair development and enhance acid phosphatase activity and Pi transporter expression levels, consequently improving the Pi absorption capacity and conferring plant tolerance to Pi deficiency.
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Proteínas de Arabidopsis , Arabidopsis , Azospirillum brasilense , Fosfatasa Ácida/genética , Fosfatasa Ácida/metabolismo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Azospirillum brasilense/metabolismo , Fosfatos/metabolismo , Fósforo/metabolismo , Raíces de Plantas/metabolismoRESUMEN
Forage pea (Pisum sativum ssp. arvense (L.) Poir.) is an important legume crop for fresh and dry herbage production with high input costs as irrigation and fertilization. Selection and breeding of accessions for improved drought tolerance, water, and mineral uptake efficiency become a necessity, rather than a choice. This study evaluated a set of forage pea accessions for the seedling root system architecture diversity and seed reserve utilization, under controlled conditions. Eight cultivars and an elite breeding line were evaluated for the first time in a plexiglass system. The number and lengths of the roots in each depth zone (0, 5, 10, 15+ cm) were evaluated and significant diversity was identified. The cultivar Livioletta had the highest number of roots and total root length. There was a significant correlation between seed weight, seed reserve utilization ratio, and root system vigor. Accessions with the highest seed reserve utilization had the highest total root length and numbers. Seedling root system vigor seems to be effective in predicting the fate of the accessions through maturity. The results suggested a possibility of "seedling root selection" for forage crop breeding.
A ervilha forrageira (Pisum sativum ssp. arvense (L.) Poir.) é uma cultura leguminosa importante para a produção de forragem fresca e seca com alto custo de insumos como irrigação e fertilização. A seleção e reprodução de acessos para melhor tolerância à seca, eficiência de absorção de água e minerais tornam-se uma necessidade, ao invés de uma escolha. Este trabalho teve como objetivo avaliar um conjunto de acessos de ervilha forrageira quanto à diversidade da arquitetura do sistema radicular de mudas e utilização de reservas de sementes, em condições controladas. Oito cultivares e uma linha de melhoramento de elite foram avaliados pela primeira vez em um sistema de plexiglass. O número e o comprimento das raízes em cada zona de profundidade (0, 5, 10, 15+ cm) foram avaliados e uma diversidade significativa foi identificada. A cultivar Livioletta apresentou o maior número de raízes e comprimento total de raízes. Houve uma correlação significativa entre o peso da semente, a taxa de utilização de reserva de semente e o vigor do sistema radicular. Os acessos com a maior utilização de reserva de sementes tiveram o maior comprimento e número total de raízes. O vigor do sistema radicular de mudas parece ser eficaz em predizer o destino dos acessos até a maturidade. Os resultados sugerem a possibilidade de "seleção de raízes de mudas" para o melhoramento da cultura forrageira.
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Raíces de Plantas/crecimiento & desarrollo , Pisum sativum/crecimiento & desarrollo , Pisum sativum/genética , Banco de SemillasRESUMEN
Genetic mechanisms controlling root development are well-understood in plant model species, and emerging frontier research is currently dissecting how some of these mechanisms control root development in cacti. Here we show the patterns of root architecture development in a gradient of divergent lineages, from populations to species in Mammillaria. First, we show the patterns of variation in natural variants of the species Mammillaria haageana. Then we compare this variation to closely related species within the Series Supertexta in Mammillaria (diverging for the last 2.1 million years) in which M. haageana is inserted. Finally, we compared these patterns of variation to what is found in a set of Mammillaria species belonging to different Series (diverging for the last 8 million years). When plants were grown in controlled environments, we found that the variation in root architecture observed at the intra-specific level, partially recapitulates the variation observed at the inter-specific level. These phenotypic outcomes at different evolutionary time-scales can be interpreted as macroevolution being the cumulative outcome of microevolutionary phenotypic divergence, such as the one observed in Mammillaria accessions and species.
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Auxin Response Factors (ARFs) constitute a large family of transcription factors that mediate auxin-regulated developmental programs in plants. ARF2, ARF3, and ARF4 are post-transcriptionally regulated by the microRNA390 (miR390)/trans-acting small interference RNA 3 (TAS3) module through the action of TAS3-derived trans - acting small interfering RNAs (ta-siRNA). We have previously reported that constitutive activation of the miR390/TAS3 pathway promotes elongation of lateral roots but impairs nodule organogenesis and infection by rhizobia during the nitrogen-fixing symbiosis established between Medicago truncatula and its partner Sinorhizobium meliloti. However, the involvement of the targets of the miR390/TAS3 pathway, i.e., MtARF2, MtARF3, MtARF4a, and MtARF4b, in root development and establishment of the nitrogen-fixing symbiosis remained unexplored. Here, promoter:reporter fusions showed that expression of both MtARF3 and MtARF4a was associated with lateral root development; however, only the MtARF4a promoter was active in developing nodules. In addition, up-regulation of MtARF2, MtARF3, and MtARF4a/b in response to rhizobia depends on Nod Factor perception. We provide evidence that simultaneous knockdown of MtARF2, MtARF3, MtARF4a, and MtARF4b or mutation in MtARF4a impaired nodule formation, and reduced initiation and progression of infection events. Silencing of MtARF2, MtARF3, MtARF4a, and MtARF4b altered mRNA levels of the early nodulation gene nodulation signaling pathway 2 (MtNSP2). In addition, roots with reduced levels of MtARF2, MtARF3, MtARF4a, and MtARF4b, as well as arf4a mutant plants exhibited altered root architecture, causing a reduction in primary and lateral root length, but increasing lateral root density. Taken together, our results suggest that these ARF members are common key players of the morphogenetic programs that control root development and the formation of nitrogen-fixing nodules.
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Plant growth promoting rhizobacteria influence host functional and adaptive traits via complex mechanisms that are just started to be clarified. Azospirillum brasilense acts as a probiotic bacterium, but detailed information about its molecular mechanisms of phytostimulation is scarce. Three interaction systems were established to analyze the impact of A. brasilense Sp245 on the phenotype of Arabidopsis seedlings, and underlying molecular responses were assessed under the following growth conditions: (1) direct contact of roots with the bacterium, (2) chemical communication via diffusible compounds produced by the bacterium, (3) signaling via volatiles. A. brasilense Sp245 improved shoot and root biomass and lateral root production in the three interaction systems assayed. Cell division, quiescent center, and differentiation protein reporters pCYCB1;1::GUS, WOX5::GFP, and pAtEXP7::GUS had a variable expression in roots depending of the nature of interaction. pCYCB1;1::GUS and WOX5::GFP increased with volatile compounds, whereas pAtEXP7::GUS expression was enhanced towards the root tip in plants with direct contact with the bacterium. The auxin reporter DR5::GUS was highly expressed with diffusible and volatile compounds, and accordingly, auxin signaling mutants pin3, slr1, arf7arf19, and tir1afb2afb3 showed differential phytostimulant responses when compared with the wild type. By contrast, ethylene signaling was not determinant to mediate root changes in response to the different interactions, as observed using the ethylene-related mutants etr1, ein2, and ein3. Our data highlight the diverse effects by which A. brasilense Sp245 improves plant growth and root architectural traits and define a critical role of auxin but not ethylene in mediating root response to bacterization.
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Arabidopsis/química , Azospirillum brasilense/química , Desarrollo de la Planta/fisiología , Raíces de Plantas/crecimiento & desarrolloRESUMEN
Soil salinity is a key problem for crop production worldwide. High salt concentration in soil negatively modulates plant growth and development. In roots, salinity affects the growth and development of both primary and lateral roots. The phytohormone auxin regulates various developmental processes during the plant's life cycle, including several aspects of root architecture. Auxin signaling involves the perception by specialized receptors which module several regulatory pathways. Despite their redundancy, previous studies have shown that their functions can also be context-specific depending on tissue, developmental or environmental cues. Here we show that the over-expression of Auxin Signaling F-Box 3 receptor results in an increased resistance to salinity in terms of root architecture and germination. We also studied possible downstream signaling components to further characterize the role of auxin in response to salt stress. We identify the transcription factor SZF1 as a key component in auxin-dependent salt stress response through the regulation of NAC4. These results give lights of an auxin-dependent mechanism that leads to the modulation of root system architecture in response to salt identifying a hormonal cascade important for stress response.
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Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Germinación/genética , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Raíces de Plantas/metabolismo , Receptores de Superficie Celular/metabolismo , Estrés Salino/genética , Factores de Transcripción/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas/genética , Germinación/efectos de los fármacos , Péptidos y Proteínas de Señalización Intracelular/genética , Meristema/efectos de los fármacos , Meristema/genética , Meristema/metabolismo , Mutación , Raíces de Plantas/efectos de los fármacos , Raíces de Plantas/genética , Plantas Modificadas Genéticamente , Receptores de Superficie Celular/genética , Salinidad , Estrés Salino/efectos de los fármacos , Transducción de Señal/efectos de los fármacos , Transducción de Señal/genética , Factores de Transcripción/genética , Regulación hacia ArribaRESUMEN
The experiment was conducted in the 2016/17 crop season in a greenhouse at Passo Fundo University, Brazil. We hypothesised that the morphological characteristics and biochemical and anatomical composition of soybean roots and shoots, when competing with weeds during different growth periods, are negatively affected, so current concepts of competition between plants should also consider changes in plant roots. The soybean cultivar P 95R51 and horseweed (Conyza bonariensis) were used. The treatments consisted of the presence or absence of weeds during different coexistence periods of soybean with horseweed. The periods were V0-V3, V0-V6, V0-R2, V3-R6, V6-R6 and R2-R6, where V0 was the date of soybean sowing and V3, V6, R2 and R6 were phenological stages of the crop. Two fresh roots were used to examine morphological traits. Four roots were used for quantification of dry matter and secondary metabolites. Root length was reduced by 21%, 14% and 20% when competing with a weed in the V0-V3, V0-V6 and R2-R6 coexistence periods, respectively. Total phenol content in the V0-V6 and V0-R2 periods was reduced when plants were in competition with weeds; a similar trend was found for flavonoids in the V0-V6 period. Soybean-horseweed competition from crop emergence to the V6 stage, in general, affects shoot and root morphological traits and the biochemical composition of the soybean roots. The presence of horseweed at the V3, V6 and R2 stages does not negatively alter the traits evaluated. Root anatomical composition is not modified during all coexistence periods with horseweed.
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Glycine max , Raíces de Plantas , Brasil , Raíces de Plantas/anatomía & histología , Malezas/fisiología , Glycine max/química , Glycine max/fisiologíaRESUMEN
ALTERED MERISTEM PROGRAM 1 (AMP1) encodes a putative glutamate-carboxypeptidase important for plant growth and development. In this study, by comparing the growth of Arabidopsis wild-type, amp1-10 and amp1-13 mutants, and AMP1-GFP/OX2- and AMP1-GFP/OX7-overexpressing seedlings in vitro and in soil, we uncover the role of AMP1 in biomass accumulation in Arabidopsis. AMP1-overexpressing plants had longer primary roots and increased lateral root number and density than the WT, which correlated with improved root, shoot, and total biomass accumulation. AMP1-overexpressing seedlings had an enhanced rate of growth of primary roots, and accordingly, sucrose supplementation restored primary root growth and promoted lateral root formation in amp1 mutants, while reproductive development, fruit size, and seed content were also modified according to disruption or overexpression of AMP1. We further found that AMP1 plays an important role for stomatal development, guard cell functioning, and carbon assimilation. These data help explain the pleiotropic functions of AMP1 in both root and shoot system development, possibly acting in a sugar-dependent manner for regulation of root architecture, biomass accumulation, and seed production.
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Regulación de la Expresión Génica de las Plantas/genética , Meristema/metabolismo , Fotosíntesis/genética , Arabidopsis/genética , BiomasaRESUMEN
MAIN CONCLUSION: CRK28, a cysteine-rich receptor-like kinase, plays a role in root organogenesis and overall growth of plants and antagonizes abscisic acid response in seed germination and primary root growth. Receptor-like kinases (RLK) orchestrate development and adaptation to environmental changes in plants. One of the largest RLK groups comprises cysteine-rich receptor-like kinases (CRKs), for which the function of most members remains unknown. In this report, we show that the loss of function of CRK28 led to the formation of roots that are longer and more branched than the parental (Col-0) plantlets, and this correlates with an enhanced domain of the mitotic reporter CycB1:uidA in primary root meristems, whereas CRK28 overexpressing lines had the opposite phenotype, including slow root growth and reduced lateral root formation. Epidermal cell analyses revealed that crk28 mutants had reduced root hair length and increased trichome number, whereas 35S::CRK28 lines present primary roots with longer root hairs but lesser trichomes in leaves. The overall growth in soil of crk28 mutant and CRK28 overexpressing lines was reduced or enhanced, respectively, when compared to the parental (Col-0) seedlings, while germination, root growth and expression analyses of ABI3 and ABI5 further showed that CRK28 modulates ABA responses, which may be important to fine-tune plant morphogenesis. Our study unravels the participation of RLK signaling in root growth and epidermal cell differentiation.
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Ácido Abscísico/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas , Proteínas Serina-Treonina Quinasas/genéticaRESUMEN
Root architecture is a complex structure that comprises multiple traits of the root phenotype. Novel platforms and models have been developed to better understand root architecture. In this methods paper, we introduce a novel allometric model, named rhizochron index (m), which describes lateral root (LR) branching and elongation patterns across the primary root (PR). To test our model, we obtained data from 16 natural accessions of Arabidopsis thaliana at three stages of early root development to measure conventional traits of root architecture (e.g., PR and LR length), and extracted the rhizochron index (m). In addition, we tested previously published datasets to assess the utility of the rhizochron index (m) to distinguish mutants and environmental effects on root architecture. Our results indicate that rhizochron index (m) is useful to distinguish the natural variations of root architecture between A. thaliana accessions, but not across early stages of root development. Correlation analyses in these accessions showed that m is a novel trait that partially captures information from other root architecture traits such as total lateral root length, and the ratio between lateral root and primary root lengths. Moreover, we found that the rhizochron index was useful to distinguish ABA effect on root architecture, as well as the mutant pho1 phenotype. We propose the rhizochron index (m) as a new feature of the root architectural system to be considered, in addition to conventional traits in future investigations.
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Bacteria rely on chemical communication to sense the environment and to retrieve information on their population densities. Accordingly, a vast repertoire of molecules is released, which synchronizes expression of genes, coordinates behavior through a process termed quorum-sensing (QS), and determines the relationships with eukaryotic species. Already identified QS molecules from Gram negative bacteria can be grouped into two main classes, N-acyl-L-homoserine lactones (AHLs) and cyclodipeptides (CDPs), with roles in biofilm formation, bacterial virulence or symbiotic interactions. Noteworthy, plants detect each of these molecules, change their own gene expression programs, re-configurate root architecture, and activate defense responses, improving in this manner their adaptation to natural and agricultural ecosystems. AHLs may act as alarm signals, pathogen and/or microbe-associated molecular patterns, whereas CDPs function as hormonal mimics for plants via their putative interactions with the auxin receptor Transport Inhibitor Response1 (TIR1). A major challenge is to identify the molecular pathways of QS-mediated crosstalk and the plant receptors and interacting proteins for AHLs, CDPs and related signals.
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Raíces de Plantas/microbiología , Percepción de Quorum/fisiología , Rhizobiaceae/metabolismo , Interacciones Huésped-Patógeno , Raíces de Plantas/anatomía & histología , Raíces de Plantas/fisiologíaRESUMEN
Morphogenetic processes are the basis of new organ formation. Lateral roots (LRs) are the building blocks of the root system. After LR initiation and before LR emergence, a new lateral root primordium (LRP) forms. During this period, the organization and functionality of the prospective LR is defined. Thus, proper LRP morphogenesis is a decisive process during root system formation. Most current studies on LRP morphogenesis have been performed in the model species Arabidopsis thaliana; little is known about this process in other angiosperms. To understand LRP morphogenesis from a wider perspective, we review both contemporary and earlier studies. The latter are largely forgotten, and we attempted to integrate them into present-day research. In particular, we consider in detail the participation of parent root tissue in LRP formation, cell proliferation and timing during LRP morphogenesis, and the hormonal and genetic regulation of LRP morphogenesis. Cell type identity acquisition and new stem cell establishement during LRP morphogenesis are also considered. Within each of these facets, unanswered or poorly understood questions are identified to help define future research in the field. Finally, we discuss emerging research avenues and new technologies that could be used to answer the remaining questions in studies of LRP morphogenesis.
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Transcriptional regulation of gene expression influences plant growth, environmental interactions and plant-plant communication. Here, we report that population density is a key factor for plant productivity and a major root architectural determinant in Arabidopsis thaliana. When grown in soil at varied densities from 1 to 32 plants, high number of individuals decreased stem growth and accelerated senescence, which negatively correlated with total plant biomass and seed production at the completion of the life cycle. Root morphogenesis was also a major trait modulated by plant density, because an increasing number of individuals grown in vitro showed repression of primary root growth, lateral root formation and root hair development while affecting auxin-regulated gene expression and the levels of auxin transporters PIN1 and PIN2. We also found that mutation of the Mediator complex subunit PFT1/MED25 renders plants insensitive to high density-modulated root traits. Our results suggest that plant density is critical for phase transitions, productivity and root system architecture and reveal a role of Mediator in self-plant recognition.