Lateral Root Growth Research Articles

РОЛЬ АУКСИНОВ И ИХ ПЕРЕНОСЧИКОВ ПРИ НИЗКОЙ ИНТЕНСИВНОСТИ СВЕТА В РЕГУЛЯЦИИ ВЕТВЛЕНИЯ КОРНЕЙ ПШЕНИЦЫ

Light is vital for any plant, so there are many mechanisms for adapting to its deficiency. For example, when shading by other plants, the stems are elongated due to the resources going to other organs, in particular, roots, the branching of which may decrease. The decrease in root branching under the influence of low light is explained by a decrease in auxin transport (IAA) from shoots to roots. However, data on the effect of low light on auxins is rather contradictory. The data obtained in this work indicate a decrease in the concentration of auxins in the roots and phloem exudate of plants at low light intensity, which indicates the role of auxins in the transmission of a signal from the shoot about this external factor and its effect on the level of auxins in roots. The root growth response to low light was manifested as a decrease in branching, and since auxins are known to be required to induce lateral root growth, this low light effect appears to be related to the long-range signal from the leaves in the form of reduced delivery of auxins through the phloem.

Does Sulfoquinovosyl Diacylglycerol Synthase OsSQD1 Affect the Composition of Lipids in Rice Phosphate-Deprived Root?

Lipids are the essential components of the cell intracellular and plasma membranes. Sulfoquinovosyldiacylglycerol (SQDG) is a glycolipid; glycolipids can replace phospholipids in maintaining phosphate (Pi) homeostasis in plants which are undergoing Pi starvation. Sulfoquinovosyl diacylglycerol synthase 1 (OsSQD1) is a critical enzyme in the first step of catalyzation in the formation of SQDG in rice. In this study, the expression pattern of different zones in roots of OsSQD1 in response to different Pi conditions is examined, and it is found that OsSQD1 is highly expressed in lateral roots under Pi-sufficient and -deficient conditions. The root phenotype observation of different OsSQD1 transgenic lines suggests that the knockout/down of OsSQD1 inhibits the formation and growth of lateral roots under different Pi conditions. Additionally, the lipid concentrations in OsSQD1 transgenic line roots indicate that OsSQD1 knockout/down decreases the concentration of phospholipids and glycolipids in Pi-starved roots. The OsSQD1 mutation also changes the composition of different lipid species with different acyl chain lengths, mainly under Pi-deprived conditions. The relative transcript expression of genes relating to glycolipid synthesis and phospholipid degradation is estimated to help study the mechanism by which OsSQD1 exerts an influence on the alteration of lipid composition and concentration in Pi-starved roots. Moreover, in Pi-starved roots, the knockout of OsSQD1 decreases the unsaturated fatty acid content of phospholipids and glycolipids. To summarize, the present study demonstrates that OsSQD1 plays a key role in the maintenance of phospholipid and glycolipid composition in Pi-deprived rice roots, which may influence root growth and development under Pi-deprived conditions.

24-epibrassinolide improves cadmium tolerance and lateral root growth associated with regulating endogenous auxin and ethylene in Kentucky bluegrass

The application of phytohormones is a viable technique to increase the efficiency of phytoremediation in heavy metal-contaminated soils. The objective of this study was to determine how the application of 24-epibrassinolide (EBR), a brassinosteroid analog, could regulate root growth and tolerance to cadmium (Cd) stress in Kentucky bluegrass. As a result, the number of lateral root primordia and total root length in the Cd-treated seedlings decreased by 33.1 % and 56.5 %, respectively. After the application of EBR, Cd accumulation in roots and leaves, and the negative effect of Cd on root growth were reduced under Cd stress. Additionally, the expression of the brassinosteroid signaling gene PpBRI1 was significantly upregulated by exogenous EBR. Moreover, exogenous EBR upregulated the expression of genes encoding antioxidant enzymes and improved the activity of antioxidant enzymes, thereby reduced oxidative stress in roots. Finally, targeted hormonomics analysis highlighted the utility of the application of EBR to alleviate the effect of Cd on the reduction in auxin (IAA) content and the increase in ethylene (ACC) content. These were known to be associated with the upregulation in the expression of auxin biosynthesis gene PpYUCCA1 and downregulation in the expression of ethylene biosynthesis gene PpACO1 in the roots treated with Cd stress. Overall, the application of EBR alleviated Cd-induced oxidative stress in addition to improving root elongation and lateral root growth crosstalk with auxin and ethylene in Kentucky bluegrass subjected to Cd stress. This study further highlights the potential role of brassinosteroids in improving the efficiency of phytoremediation for Cd-contaminated soils.

ROLE OF MYCORRHIZA HELPER BACTERIA ON MYCORRHIZAL COLONIZATION AND NEMATODE Pratylenchus coffeae INFECTION

The coffee nursery is susceptible to endoparasitic Pratylenchus coffeae. Application of biological method in the nursery is suggested to control the nematode population and maintain the seedling health. The objectives of this study were to observe the ability of Arbuscular Mycorrhiza Fungi (AMF) Glomus spp. and liquid inoculant of Mycorrhiza Helper Bacteria (MHB) consortium Pseudomonas diminuta and Bacillus subtilis for increasing AMF colonization and reducing the infection P. coffeae in Arabica coffee seedling and their growth. A pot experiment was conducted using a Completely Randomized Block Design with four treatments and five replications. The treatments were Glomus spp. spore inoculation without and with two concentrations of MHB. The control treatment did not receive Glomus spp. and MHB. The seedlings were growing in the greenhouse for three months. The results indicated that Glomus spp. and MHB consortium significantly reduced the nematode total number in soil and roots by approximately 30%; and infection degree of P. coffeae by 50%. The application of Glomus spp. significantly increased root colonization by mycorrhizal fungi, but MHB inoculation did not affect the mycorrhizal colonization. Seedlings treated with MHB had higher shoot length compared to the plant without MHB and control; but the leaves number and shoot dry weight of seedlings were not affected by all treatments. Even though the root fresh weight was reduced after MHB treatment, the lateral roots growth of MHB-treated seedling visually was improved. The experiment demonstrated that MHB was efficient to reduce P. coffeae infection of Arabica seedling.

Изучение холодостойкости сортообразцов сахарной кукурузы

The article discusses the results of a studying the resistance to suboptimal temperatures of sweet corn varieties in laboratory and field conditions on the basis of the Federal State Budget-ary Institution RosNIISK "Rossorgo". For the laboratory experiment, the roll method of cold germination (coldtest) modified by N.I. Kiyashko was used. During the studying, it was revealed that none of the studied samples is cold tolerant. High germination rates (>80%) were found in genotypes: k-3151, k-4475, k-103, k-4456, k-13807, Zabava, Zukerka, Zabava/Delight. These samples can be considered resistant to suboptimal temperatures. The measurements of the length of the seedlings and the counting of the lateral roots were carried out in the experiment and in the control. It was found that, on average, the length of sprouts and roots decreased by 56.3 and 47.1%, respectively. Prolonged exposure to cold on the Zabava genotype had practically no ef-fect on the activation of the growth processes of roots and green mass. In most of the studied samples, the effect of suboptimal temperatures contributed to the growth of lateral roots. A genotype with a high germination rate in laboratory and field conditions was revealed - k-4456. Samples k-103 (I1), Zabava, Zabava/Uslada, which were recorded as cold-resistant in laboratory conditions, were classified as medium-resistant in the field. A significant correlation was also established between the germination of test samples and the preservation of germination (r=0.91). There was no relationship between the other studied features. Keywords: SUGAR CORN, POTENTIAL COLD RESISTANCE, COLD RESISTANCE, LABORATO-RY GENERATION, GENERATION RESERVATION, CORRELATION

Low nitrogen supply inhibits root growth but prolongs lateral root lifespan in cotton

Primary and lateral roots are the main components of the root system in cotton, and their development and lifespan are critical for the uptake of water and nutrients (e.g., nitrogen). However, the responses of the daily growth dynamics and lifespan of cotton roots to low nitrogen are poorly understood. In this study of the whole growth period of cotton plants, two cotton cultivars (K836 and K837) were grown in pots in a greenhouse with 138 mg·kg-1 nitrogen fertilizer as the control (normal nitrogen) and no nitrogen fertilizer as the low nitrogen treatment. The growth of primary and lateral roots was investigated using the in situ root phenotyping platform RhizoPot. The root responses of both cultivars to low nitrogen were consistent except for the correlation between lateral root diameter and length on the 11th d after lateral root emergence. Root growth was significantly inhibited under low nitrogen, manifested as substantial reductions in root length, surface area, volume, and dry matter weight, which decreased by 23.91–26.88 %, 34.92–37.59 %, 32.71–37.94 %, and 17.92–21.62 %, respectively, in comparison with the control. Low nitrogen treatment reduced the diameter of primary roots by shortening the duration of its rapid accumulation, by 7.54–10.92 d. The smaller diameter of lateral roots was owing to low nitrogen treatment increasing the proportion of finer roots compared to the control. The effect of low nitrogen on the thickening rate of lateral roots showed stage-specific differences accompanied by elongation of lateral roots. In the early stage, the lateral root length of the low nitrogen treatment was longer than that of the control because lateral root elongation was higher, while the opposite pattern was observed in the later stage. Low nitrogen treatment significantly increased the lifespan of both the primary and secondary lateral roots, by 3.84–3.93 d and 4.95–5.46 d, respectively. Detailed studies revealed that low nitrogen treatment induced the greatest increase in the survival of lateral roots with larger diameters. Collectively, the results of this study indicate low nitrogen treatment not only reduced primary root thickness, but also resulted in shorter and thinner lateral roots with a longer lifespan relative to the normal nitrogen treatment.

High-throughput and automatic structural and developmental root phenotyping on Arabidopsis seedlings

BackgroundHigh-throughput phenotyping is crucial for the genetic and molecular understanding of adaptive root system development. In recent years, imaging automata have been developed to acquire the root system architecture of many genotypes grown in Petri dishes to explore the Genetic x Environment (GxE) interaction. There is now an increasing interest in understanding the dynamics of the adaptive responses, such as the organ apparition or the growth rate. However, due to the increasing complexity of root architectures in development, the accurate description of the topology, geometry, and dynamics of a growing root system remains a challenge.ResultsWe designed a high-throughput phenotyping method, combining an imaging device and an automatic analysis pipeline based on registration and topological tracking, capable of accurately describing the topology and geometry of observed root systems in 2D + t. The method was tested on a challenging Arabidopsis seedling dataset, including numerous root occlusions and crossovers. Static phenes are estimated with high accuracy (R^2=0.996 and 0.923 for primary and second-order roots length, respectively). These performances are similar to state-of-the-art results obtained on root systems of equal or lower complexity. In addition, our pipeline estimates dynamic phenes accurately between two successive observations (R^2=0.938 for lateral root growth).ConclusionsWe designed a novel method of root tracking that accurately and automatically measures both static and dynamic parameters of the root system architecture from a novel high-throughput root phenotyping platform. It has been used to characterise developing patterns of root systems grown under various environmental conditions. It provides a solid basis to explore the GxE interaction controlling the dynamics of root system architecture adaptive responses. In future work, our approach will be adapted to a wider range of imaging configurations and species.

Galic acid as a non-specific regulator of phenol synthesis and growth of regenerate plants of Corylus avellana (L.) H. Karst. and Salix alba L. in vitro

Gallic acid is found in plant tissues in free form, as well as in the composition of complex esters and hydrolysed tannins. These phenolic compounds have significant antioxidant activity and protect plant cells from damage by free radicals. In the conditions of stress that occurs during the introduction of plants into in vitro culture, the vast majority of explants are characterised by an intensive synthesis of phenols, which quickly oxidise, polymerise, block the explants’ nutrition pathways, and cause tissue necrosis. The addition of gallic acid in millimolar concentrations to the nutrient medium reduces the risk of autointoxication of tissues by secondary metabolic products. The purpose of this study was to investigate the effect of exogenous gallic acid on organogenesis and phenolic synthesis of Salix alba and Corylus avellana plants in vitro. For this purpose, the study used methods of tissue and organ culture in vitro, spectrophotometric determination of total phenols and flavonoids in leaves, methods of dispersion and nonparametric analysis. It was established that gallic acid at a concentration of 1 mmol·l-1 in the composition of the DKW nutrient medium caused the awakening of dormant buds, stimulated the growth of shoots, and also promoted the branching of stems, the development and growth of lateral roots of Salix alba in vitro. It also inhibited the synthesis of phenols in Corylus avellana plants of the varieties ‘Tonda Romana’, ‘Tonda Gentile Dele Lange’, ‘Barcelona’, while contributing to an increase in the content of phenolic compounds in the leaves of the varieties ‘Tonda Di Giffoni’, ‘Mortarella’, and ‘Epsilon’. It was established that the varieties recommended for fruiting have a higher content of phenolic compounds (‘Tonda Gentile Dele Lange’ and ‘Tonda Di Giffoni’) compared to pollinator varieties (‘Mortarella’). Therefore, exogenous gallic acid at a concentration of 1 mmol·l-1 has the properties of a non-specific regulator of phenol synthesis in regenerating plants of hazel (Corylus avellana), which is relevant for plants with a high content of phenols, especially at the stage of their introduction into in vitro culture

Root uptake dominates mercury accumulation in permafrost plants of Qinghai-Tibet Plateau

Uptake of atmospheric elemental mercury via foliage is thought to be the dominant pathway of mercury accumulation in terrestrial ecosystems, including those in the Arctic permafrost regions. Whether a similar process operates in alpine permafrost regions remains unknown. Here we report mercury concentrations and stable isotopic signatures in a large cluster alpine permafrost regions of mid-latitude Qinghai-Tibet Plateau. We find a transition from foliage to root uptake of mercury as elevation increases. In alpine permafrost regions, we find that root uptake of mercury from the surrounding soil is the dominant accumulation pathway. We estimate that root uptake accounts for 70 ± 19% of plant mercury in permafrost regions of the Qinghai-Tibet Plateau and propose that this may be related to the harsh climate conditions suppressing foliage growth and promoting lateral root growth.

Co-expression of stress-responsive regulatory genes, MuNAC4, MuWRKY3 and MuMYB96 associated with resistant-traits improves drought adaptation in transgenic groundnut (Arachis hypogaea l.) plants.

Groundnut, cultivated under rain-fed conditions is prone to yield losses due to intermittent drought stress. Drought tolerance is a complex phenomenon and multiple gene expression required to maintain the cellular tolerance. Transcription factors (TFs) regulate many functional genes involved in tolerance mechanisms. In this study, three stress-responsive regulatory TFs cloned from horse gram, (Macrotyloma uniflorum (Lam) Verdc.), MuMYB96, involved in cuticular wax biosynthesis; MuWRKY3, associated with anti-oxidant defense mechanism and MuNAC4, tangled with lateral root development were simultaneously expressed to enhance drought stress resistance in groundnut (Arachis hypogaea L.). The multigene transgenic groundnut lines showed reduced ROS production, membrane damage, and increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) enzyme activity, evidencing improved antioxidative defense mechanisms under drought stress. Multigene transgenic plants showed lower proline content, increased soluble sugars, epicuticular wax content and higher relative water content suggesting higher maintenance of tissue water status compared to wildype and mock plants. The scanning electron microscopy (SEM) analysis showed a substantial increase in deposition of cuticular waxes and variation in stomatal number in multigene transgenic lines compared to wild type and mock plants. The multigene transgenic plants showed increased growth of lateral roots, chlorophyll content, and stay-green nature in drought stress compared to wild type and mock plants. Expression analysis of transgenes, MuMYB96, MuWRKY3, and MuNAC4 and their downstream target genes, KCS6, KCR1, APX3, CSD1, LBD16 and DBP using qRT-PCR showed a two- to four-fold increase in transcript levels in multigene transgenic groundnut plants over wild type and mock plants under drought stress. Our study demonstrate that introducing multiple genes with simultaneous expression of genes is a viable option to improve stress tolerance and productivity under drought stress.

WRKY29 transcription factor regulates ethylene biosynthesis and response in arabidopsis

The gaseous phytohormone ethylene participates in a lot of physiological processes in plants. 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS, EC 4.4.1.14) and the ACC oxidase (ACO, EC 1.14.17.4) are key enzymes in ethylene biosynthesis. However, how ACSs and ACOs are regulated at the transcriptional level is largely unknown. In the present study, we showed that an Arabidopsis (Arabidopsis thaliana) WRKY-type transcription factor (TF), WRKY29 positively regulated the expression of ACS5, ACS6, ACS8, ACS11 and ACO5 genes and thus promoted basal ethylene production. WRKY29 protein was localized in nuclei and was a transcriptional activator. Overexpression of WRKY29 caused pleiotropic effect on plant growth, development and showed obvious response even without ACC treatment. Inducible overexpression of WRKY29 also reduced primary root elongation and lateral root growth. A triple response assay of overexpression and mutant seedlings of WRKY29 showed that overexpression seedlings had shorter hypocotyls than the transgenic GFP (Green Fluorescence Protein) control, while mutants had no difference from wild-type. A qRT-PCR assay demonstrated that expression of multiple ACSs and ACO5 was up-regulated in WRKY29 overexpression plants. A transactivation assay through dual luciferase reporter system confirmed the regulation of promoters of ACS5, ACS6, ACS8, ACS11 and ACO5 by WRKY29. Both in vivo chromatin immunoprecipitation (ChIP)- quantitative PCR and in vitro electrophoretic mobility shift assay (EMSA) revealed that WRKY29 directly bound to the promoter regions of its target genes. Taken together, these results suggest that WRKY29 is a novel TF positively regulating ethylene production by modulating the expression of ACS and ACO genes.

Genome-Wide Identification of Sucrose Transporter Genes and Functional Analysis of RsSUC1b in Radish (Raphanus sativus L.)

In most higher plants, sucrose is the significant form of carbohydrate for long-distance transportation. Sucrose transporters/sucrose carriers (SUTs/SUCs) are involved in the loading and unloading of sucrose in phloem and play an important role in the growth and development of plants. In this study, 12 RsSUC genes were first identified from the radish genome, and their phylogenetic relationships, gene structure, and conserved motifs were further analyzed. RT-qPCR results indicated that RsSUC genes exhibited various expression patterns in different tissues and development stages of the radish. Overexpression of RsSUC1b in Arabidopsis significantly improved the uptake efficiency of exogenous sucrose, and promoted leaves and lateral root growth. In addition, the transgenic plants flowered significantly earlier than wild-type (WT) plants, and the soluble sugar contents (SSCs) including sucrose, glucose, and fructose in the mature leaves and pods were increased. It could be inferred that RsSUC1b is a plasma membrane sucrose transporter and plays a vital role in sucrose transportation and sugar accumulation during plant growth and development. These findings provided novel insights into the biological function of RsSUC genes and facilitate dissecting the molecular mechanism underlying sugar transport during radish development.

Natural variation and domestication selection of ZmSULTR3;4 is associated with maize lateral root length in response to salt stress.

Soil salinity is a major constraint that restricts crop productivity worldwide. Lateral roots (LRs) are important for water and nutrient acquisition, therefore understanding the genetic basis of natural variation in lateral root length (LRL) is of great agronomic relevance to improve salt tolerance in cultivated germplasms. Here, using a genome-wide association study, we showed that the genetic variation in ZmSULTR3;4, which encodes a plasma membrane-localized sulfate transporter, is associated with natural variation in maize LRL under salt stress. The transcript of ZmSULTR3;4 was found preferentially in the epidermal and vascular tissues of root and increased by salt stress, supporting its essential role in the LR formation under salt stress. Further candidate gene association analysis showed that DNA polymorphisms in the promoter region differentiate the expression of ZmSULTR3;4 among maize inbred lines that may contribute to the natural variation of LRL under salt stress. Nucleotide diversity and neutrality tests revealed that ZmSULTR3;4 has undergone selection during maize domestication and improvement. Overall, our results revealed a regulatory role of ZmSULTR3;4 in salt regulated LR growth and uncovered favorable alleles of ZmSULTR3;4, providing an important selection target for breeding salt-tolerant maize cultivar.

The miR156 juvenility factor and PLETHORA 2 form a regulatory network and influence timing of meristem growth and lateral root emergence.

Plants develop throughout their lives: seeds become seedlings that mature and form fruits and seeds. Although the underlying mechanisms that drive these developmental phase transitions have been well elucidated for shoots, the extent to which they affect the root is less clear. However, root anatomy does change as some plants mature; meristems enlarge and radial thickening occurs. Here, in Arabidopsis thaliana, we show that overexpressing miR156A, a gene that promotes the juvenile phase, increased the density of the root system, even in grafted plants in which only the rootstock had the overexpression genotype. In the root, overexpression of miR156A resulted in lower levels of PLETHORA 2, a protein that affects formation of the meristem and elongation zone. Crossing in an extra copy of PLETHORA 2 partially rescued the effects of miR156A overexpression on traits affecting root architecture, including meristem length and the rate of lateral root emergence. Consistent with this, PLETHORA 2 also inhibited the root-tip expression of another miR156 gene, miR156C. We conclude that the system driving phase change in the shoot affects developmental progression in the root, and that PLETHORA 2 participates in this network.

Impacts of iron on phosphate starvation-induced root hair growth in Arabidopsis.

In Arabidopsis, phosphate starvation (-Pi)-induced responses of primary root and lateral root growth are documented to be correlated with ambient iron (Fe) status. However, whether and how Fe participates in -Pi-induced root hair growth (RHG) remains unclear. Here, responses of RHG to different Fe concentrations under Pi sufficiency/deficiency were verified. Generally, distinct dosage effects of Fe on RHG appeared at both Pi levels, due to the generation of reactive oxygen species. Following analyses using auxin mutants and the phr1 mutant revealed that auxin and the central regulator PHR1 are required for Fe-triggered RHG under -Pi. A further proteomic study indicated that processes of vesicle trafficking and auxin synthesis and transport were affected by Fe under -Pi, which were subsequently validated by using a vesicle trafficking inhibitor, brefeldin A,and an auxin reporter, R2D2. Moreover, vesicle trafficking-mediated recycling of PIN2, an auxin efflux transporter, was notably affected by Fe under -Pi. Correspondingly, root hairs of pin2 mutant displayed attenuated responses to Fe under -Pi. Together, we propose that Fe affects auxin signalling probably by modulating vesicle trafficking, chiefly the PIN2 recycling, which might work jointly with PHR1 on modulating -Pi-induced RHG.

The Arabidopsis TETRATRICOPEPTIDE-REPEAT THIOREDOXIN-LIKE (TTL) family members are involved in root system formation via their interaction with cytoskeleton and cell wall remodeling.

Lateral roots (LR) are essential components of the plant edaphic interface; contributing to water and nutrient uptake, biotic and abiotic interactions, stress survival, and plant anchorage. We have identified the TETRATRICOPEPTIDE-REPEAT THIOREDOXIN-LIKE 3 (TTL3) gene as being related to LR emergence and later development. Loss of function of TTL3 leads to a reduced number of emerged LR due to delayed development of lateral root primordia (LRP). This trait is further enhanced in the triple mutant ttl1ttl3ttl4. TTL3 interacts with microtubules and endomembranes, and is known to participate in the brassinosteroid (BR) signaling pathway. Both ttl3 and ttl1ttl3ttl4 mutants are less sensitive to BR treatment in terms of LR formation and primary root growth. The ability of TTL3 to modulate biophysical properties of the cell wall was established under restrictive conditions of hyperosmotic stress and loss of root growth recovery, which was enhanced in ttl1ttl3ttl4. Timing and spatial distribution of TTL3 expression is consistent with its role in development of LRP before their emergence and subsequent growth of LR. TTL3 emerged as a component of the root system morphogenesis regulatory network.

Ectopic expression of GmNF-YA8 in Arabidopsis delays flowering via modulating the expression of gibberellic acid biosynthesis- and flowering-related genes and promotes lateral root emergence in low phosphorus conditions.

NUCLEAR FACTOR Y subunit alpha (NF-YA), together with NF-YB and NF-YC, regulates plant growth and development, as well as plant responses to biotic and abiotic stresses. Although extensive studies have examined the functions of NF-YAs in Arabidopsis thaliana, the roles of NF- YAs in Glycinme max are poorly understood. In this study, we identified a phosphorus (P) starvation-responsive NF-YA8 in soybean. The expression of GmNF-YA8 is induced by low P or low nitrogen in leaves, but not by potassium or iron starvation, respectively. GmNF-YA8 is localized in the nucleus and plasma membrane. Ectopic expression of GmNF-YA8 inhibits plant growth and delayed flowering in Arabidopsis. Exogenous application of gibberellic acid (GA) rescues the delayed flowering phenotype in Arabidopsis overexpressing GmNF-YA8 lines GmNF-YA8OE-05 and GmNF-YA8OE-20. Moreover, quantitative real time PCR (qRT-PCR) verified that overexpression of GmNF-YA8 downregulates GA20ox2 and GA3ox2 expression, but upregulates GA2ox2 and GA2ox3 that encode enzymes, which inactive bioactive GAs. Consistent with the late flowering phenotype of Arabidopsis trangenic lines that overexpress GmNF-YA8, the transcript levels of flowering-promoting genes AP1, CO, LFY, and SOC1 are reduced. In addition, overexpression of GmNF-YA8 promotes the emergence of lateral root (LR) primordium from epidermis rather than the initiation of LR in low P, and increases the LR density in low nitrogen. Our results provide insights into the roles of GmNF-YA8.

Auxin triggers pectin modification during rootlet emergence in white lupin.

Emergence of secondary roots through parental tissue is a highly controlled developmental process. Although the model plant Arabidopsis has been useful to uncover the predominant role of auxin in this process, its simple root structure is not representative of how emergence takes place in most plants, which display more complex root anatomy. White lupin is a legume crop producing structures called cluster roots, where closely spaced rootlets emerge synchronously. Rootlet primordia push their way through several cortical cell layers while maintaining the parent root integrity, reflecting more generally the lateral root emergence process in most multilayered species. In this study, we showed that lupin rootlet emergence is associated with an upregulation of cell wall pectin modifying and degrading genes under the active control of auxin. Among them, we identified LaPG3, a polygalacturonase gene typically expressed in cells surrounding the rootlet primordium and we showed that its downregulation delays emergence. Immunolabeling of pectin epitopes and their quantification uncovered a gradual pectin demethylesterification in the emergence zone, which was further enhanced by auxin treatment, revealing a direct hormonal control of cell wall properties. We also report rhamnogalacturonan-I modifications affecting cortical cells that undergo separation as a consequence of primordium outgrowth. In conclusion, we describe a model of how external tissues in front of rootlet primordia display cell wall modifications to allow for the passage of newly formed rootlets.

Host root exudates initiate a foraging preference by the root parasite Santalum album.

Haustoria of root-parasitic plants draw nutrients from the roots of host species. While recent studies have assessed host preferences of parasitic plants, how root-exuded chemicals can mediate host tropism and selection by root-parasitic plants is poorly understood. Under greenhouse conditions, we performed two pot experiments to determine whether the root parasite Santalum album selectively forages for superior hosts (N2-fixing Acacia confusa Merr. or Dalbergia odorifera T. Chen) rather than for inferior hosts (non-N2-fixing Bischofia polycarpa (levl.) Airy Shaw or Dracontomelon duperreranum Pierre), and whether S. album uses host root exudates and/or specific chemicals in these root exudates to locate and trigger haustorium formation. Lateral roots and haustoria of S. album seedlings exhibited greater growth in the direction of D. odorifera roots than toward roots from the other three hosts. Comparative metabolic analysis revealed that D. odorifera root exudates were enriched in isoflavonoid, flavonoid and flavone/flavonol biosynthesis pathways, and that the relative contents of flavonoids were significantly greater in the root exudates of D. odorifera than in those of the other three hosts. Root exudates from D. odorifera significantly promoted S. album root growth, haustorium formation and reactive oxygen species accumulation in haustoria. Our results demonstrate that the key step in plant parasitism by S. album is based on root exudation by a host plant; the exudates function as a metabolite signal that activate lateral root growth and haustorium formation. Our results also indicate that flavonoids in the root exudates could play an important role in S. album foraging activity. Information on the responses of root parasites to host root exudates and/or haustorium-inducing chemicals may be useful for selecting superior host species to plant with valuable species of root parasites.

Overexpression of Asr6, abscisic acid stress-ripening protein, enhances drought tolerance and modulates gene expression in rice (Oryza sativa L.)

Rice ( Oryza sativa L.), being a paddy crop, is particularly susceptible to drought, reducing its yield drastically. Abscisic acid stress-ripening proteins (Asr) are a family of plant-specific ABA-induced low molecular weight hydrophilic proteins encoded by the stress-regulated gene. This work substantiates the biological role of rice Asr6 against drought stress by its overexpression in rice. The Asr6 overexpressing (OE) lines showed better overall growth than wild-type (WT) plants reflected by their longer shoot length with higher biomass and enhanced density of the lateral roots. The decreased level of MDA and electrolyte leakage, higher proline content, less ROS accumulation, and enhanced antioxidant enzyme activities (SOD, APX, and CAT) were observed in OE lines as compared to WT plants during drought stress. The OE lines showed better recovery than WT plants after drought stress at the reproductive stage, in the terms of the increased number of panicles and total grain yields. The transcriptome analysis revealed that Asr6 regulates the expression of a wide spectrum of genes related to hormone metabolism, stress (abiotic and biotic), transcription factors, antioxidant activity, photosynthesis, signalling, transport and secondary metabolites. Interestingly, the genes related to jasmonic acid biosynthesis (up-regulation of LOX and AOS) and signalling (up-regulation of COI1 and down-regulation of JAZ proteins) were differentially expressed in OE lines, which were further validated by qRT-PCR analysis. Our findings demonstrate, Asr6 to be a positive regulator commonly involved in tolerance to drought stress and may regulate a novel JA-dependent signalling pathway in rice for drought tolerance. • Overexpression of Asr6 can improve drought stress tolerance in rice. • Asr6 promotes lateral root growth leading to higher root biomass as compared to wild type plants under drought condition. • Asr6 transgenic rice maintains redox homeostasis on exposure to drought. • Asr6 alters the expression of jasmonic acid biosynthesis and signalling pathway genes.