Root Plasticity Research Articles

Root physiological and morphology processes co-regulate the growth of Chinese-fir saplings in response to warming and precipitation reduction in the sub-tropical regions

Subtropical China is projected to experience elevated temperature greater than the mean global temperature increase and is accompanied by reduced precipitation. The plasticity of roots to changing environment strongly influences ecosystem feedbacks to climate change. However, knowledge gaps on the individual and combined effects of warming and precipitation reduction on root systems hinder our ability to accurately predict the growth and adaptability of forests under future climate change. To examine the effects of warming (W) and precipitation reduction (P) on roots physiology and morphology of Chinese-fir saplings, we used a randomized complete block design with factorial soil warming (ambient, ambient + 5℃) and precipitation reduction (ambient, ambient-50 %) treatments. A full excavation method was adopted to obtain roots, then we measured the root physiology (osmoregulatory substances, oxidant substances, protective enzymes, endogenous hormones), morphology (specific root length, SRL; surface root area, SRA; root tissue density, RTD). The content of carbon and nitrogen, isotopes (δ13C and δ15N); soil temperature, soil moisture and sapling growth were also measured. We found that compared with the control, W decreased the abscisic acid (IAA) content; P increased the contents of hydrogen peroxide (H2O2) and proline (Pro), and decreased the contents of IAA and cytokinin (CTK); warming plus precipitation reduction (WP) increased the Pro content, and decreased the contents of IAA and CTK. In addition, the effects of W and P on root morphology varied with soil depth and root diameter class. W, P, and WP all increased fine root SRL and SRA in deep soil. Warming and precipitation reduction could affect physiological traits (e.g. non-enzymatic substances and antioxidant enzymes) and subsequently morphological traits via influencing soil environment and root tissue chemistry. Collectively, the results indicated that Chinese-fir saplings responded to warming and precipitation reduction by comprehensive regulation of the non-enzymatic substances (e.g., osmotic substances and endogenous hormones) of fine roots and changing root morphological characteristics in deep soil.

The long-term effect of biochar application to Vitis vinifera L. reduces fibrous and pioneer root production and increases their turnover rate in the upper soil layers.

Fibrous and pioneer roots are essential in the uptake and transport of water and nutrients from the soil. Their dynamic may be influenced by the changing of soil physicochemical properties due to the addition of biochar, which, in turn, has been shown to improve plant growth and productivity in the short term. However, the long-term effects of biochar application on root dynamics are still widely unknown. In this study, we aimed to investigate the long-term effects of biochar application on grapevine fibrous and pioneer root dynamics and morphological traits in relation to soil characteristics. To this aim, grapevine plants amended in 2009 and 2010 respectively with one and two doses of biochar, were analyzed in their fibrous and pioneer root production and turnover rate, standing biomass, length, and specific root length, over two growing seasons. Our findings demonstrate that in the long term, biochar application significantly increased soil pH, nutrient availability, and water-holding capacity causing a decrease in the production of fibrous and pioneer roots which is reflected in a reduction of the root web characterized though by a higher turnover rate. Furthermore, we observed that these root morpho-dynamical changes were of higher magnitude in the upper soil layers (0-20 cm) and, at least in the long term, with no significant difference between the two doses. These results suggest that in the long term, biochar can be a powerful tool for improving soil quality, which in turn lowers carbon-cost investment toward the root production and maintenance of a reduced root web that might be directed into grapevine growth and productivity. Such effects shed some light on the root plastic and functional adaptation to modified soil conditions facilitated by the long-term application of biochar, which can be used for implementing adaptive agricultural practices to face the current climate change in a frame of sustainable agricultural policies.

The bifunctional transcription factor NAC32 modulates nickel toxicity responses through repression of root-nickel compartmentalization and activation of auxin biosynthesis

Nickel (Ni) is an important micronutrient, but excess Ni is toxic to many plant species. Currently, relatively little is known about the genetic basis of the plant responses to Ni toxicity. Here, we demonstrate that NAC32 transcription factor functions as a core genetic hub to regulate the Ni toxicity responses in Arabidopsis. NAC32 negatively regulates root-Ni concentration through the IREG2 (IRON REGULATED2) encoding a transporter. NAC32 also induces local auxin biosynthesis in the root-apex transition zone by upregulating YUCCA 7 (YUC7)/8/9 expression, which results in a local enhancement of auxin signaling in root tips, especially under Ni toxicity, thereby impaired primary root growth. By analyses of various combinations of nac32 and ireg2 mutants, as well as nac32 and yuc7/8/9 triple mutants, including high-order quadruple mutant, we demonstrated that NAC32 negatively regulates Ni stress tolerance by acting upstream of IREG2 and YUC7/8/9 to modulate their function in Ni toxicity responses. ChIPqPCR, EMSA (electrophoretic mobility shift assay) and transient dual-LUC reporter assays showed that NAC32 transcriptionally represses IREG2 expression but activates YUC7/8/9 expression by directly binding to their promoters. Our work demonstrates that NAC32 coordinates Ni compartmentation and developmental plasticity in roots, providing a conceptual framework for understanding Ni toxicity responses in plants.

Rice Yield and Grain Quality under Fluctuating Soil Moisture Stress

In rainfed lowlands and water-saving cultivation systems, rice plants are often exposed to soil moisture fluctuation (SMF). Improving yield as well as grain quality is the main target for breeding under water-stressed environments. This study investigated the effects of different water treatment on yield, growth parameters, and grain quality under field conditions in Japan for 2 years. Two rice genotypes, Nipponbare (japonica) and G3-3 (derived from Nipponbare and KDML105, indica), were grown under continuous waterlogging (CWL) and SMF conditions. As the grain quality characteristics, grain appearance, dimension, and taste parameters were evaluated as well as yield and yield components. SMF reduced the yield, and G3-3 showed a higher yield than Nipponbare under SMF, which was attributed to the higher number of spikelets per panicle. G3-3 showed a better taste score (mark) with lower protein and amylose contents compared to Nipponbare. However, G3-3 had a higher percentage of broken grains, indicating a trade-off in grain quality traits. Non-structural carbohydrate dynamics may be involved as one of the grain quality characteristics. G3-3 demonstrated a superior yield under SMF conditions and have potential to show superior grain quality, indicating that the introgressed segments of G3-3 may be responsible for the grain quality traits associated with root plasticity.

Root plasticity improves maize nitrogen use when nitrogen is limiting: an analysis using 3D plant modelling.

Plant phenotypic plasticity plays an important role in nitrogen (N) acquisition and use under nitrogen-limited conditions. However, this role has never been quantified as a function of N availability, leaving it unclear whether plastic responses should be considered as potential targets for selection. A combined modelling and experimentation approach was adopted to quantify the role of plasticity in N uptake and plant yield. Based on a greenhouse experiment we considered plasticity in two maize (Zea mays) traits: root-to-leaf biomass allocation ratio and emergence rate of axial roots. In a simulation experiment we individually enabled or disabled both plastic responses for maize stands grown across six N levels. Both plastic responses contributed to maintaining a higher N uptake, and plant productivity as N availability declined compared with stands in which plastic responses were disabled. We conclude that plastic responses quantified in this study may be a potential target trait in breeding programs for greater N uptake across N levels while it may only be important for the internal use of N under N-limited conditions in maize. Given the complexity of breeding for plastic responses, an a priori model analysis is useful to identify which plastic traits to target for enhanced plant performance.

Exploring the variability of root system architecture under drought stress in heat-tolerant spring-wheat lines

Background and aimsGlobal wheat production is under threat due to climate change, specifically heat and drought and their combination. This study aims to address the root trait responses of heat-tolerant wheat genotypes to drought.MethodsThe variability in root traits of CIMMYT wheat lines, which were previously developed for heat stress tolerance (HTWL), was evaluated alongside 10 Pakistani-approved varieties under three cultivation conditions and soil moisture levels.ResultsOur findings revealed that the plasticity of the wheat root system is highly pronounced, with rhizosphere conditions exerting a more substantial influence (5–49%) than the genotypic response (1–14%). Furthermore, in the hydroponic and pot system, we noted higher maximum-root length (1.5–1.8 fold) and root-to-shoot ratio (3.4–10.6 fold) as compared to field condition, while the root biomass was substantially higher in the field trial (3-57 fold). Nonetheless, persistent drought conditions exerted contrasting impact with reduction in most of the traits except specific root length and harvest index which were increased under drought.ConclusionsThe variation in root traits against drought indicates the potential for the development of improved genotypes that can withstand multiple stresses. Furthermore, it is crucial to consider rhizosphere conditions when selecting genotypes, as the plasticity of wheat roots may lead to misinterpretations if rhizosphere conditions are disregarded. Root dry weight and root-to-shoot ratio are more stable traits as compared to maximum root length and specific root length. It is recommended to evaluate a broader range of rhizosphere conditions to select tolerant genotypes.

Differential spatial plasticity response in common bean (Phaseolus vulgaris L.) root architecture under water stress is driven by increased root diameter, surface area and volume at deeper layers

Root plasticity enables plants to adapt to spatial and temporal changes in soil resources. In this study, 40 common bean genotypes evaluated for two root and shoot traits under irrigated and water stress. Three genotypes WB-216, WB-N-2, and WB-966 with contrasting plasticity responses were used for in-depth study. Highest positive plasticity for most root traits was found in case of WB-N2 and WB-216, whereas, WB-966 had negative plasticity for all the traits recorded. In terms of spatial plasticity for root traits in three root length sections, WB-216 was positively plastic for root diameter with progressive decrease from top to bottom sections. WB-N2 had positive plasticity values for root diameter, root surface area and root volume. WB-966 had negative plasticity for all the traits. For WB-216, the root diameter increased under drought in S1 but was almost same in bottom sections. In case of WB-N2, there was increase in root diameter in S2 and S3, but for WB-966, root diameter decreased in all sections. Similar trend was observed in all three genotypes for root surface area and volume. We report that major drivers of spatial plasticity of root architectural traits are increased root diameter, surface area and volume at deeper layers.

Integrated Transcriptomic and Metabolomic Analysis of Exogenous NAA Effects on Maize Seedling Root Systems under Potassium Deficiency.

Auxin plays a crucial role in regulating root growth and development, and its distribution pattern under environmental stimuli significantly influences root plasticity. Under K deficiency, the interaction between K+ transporters and auxin can modulate root development. This study compared the differences in root morphology and physiological mechanisms of the low-K-tolerant maize inbred line 90-21-3 and K-sensitive maize inbred line D937 under K-deficiency (K+ = 0.2 mM) with exogenous NAA (1-naphthaleneacetic acid, NAA = 0.01 mM) treatment. Root systems of 90-21-3 exhibited higher K+ absorption efficiency. Conversely, D937 seedling roots demonstrated greater plasticity and higher K+ content. In-depth analysis through transcriptomics and metabolomics revealed that 90-21-3 and D937 seedling roots showed differential responses to exogenous NAA under K-deficiency. In 90-21-3, upregulation of the expression of K+ absorption and transport-related proteins (proton-exporting ATPase and potassium transporter) and the enrichment of antioxidant-related functional genes were observed. In D937, exogenous NAA promoted the responses of genes related to intercellular ethylene and cation transport to K-deficiency. Differential metabolite enrichment analysis primarily revealed significant enrichment in flavonoid biosynthesis, tryptophan metabolism, and hormone signaling pathways. Integrated transcriptomic and metabolomic analyses revealed that phenylpropanoid biosynthesis is a crucial pathway, with core genes (related to peroxidase enzyme) and core metabolites upregulated in 90-21-3. The findings suggest that under K-deficiency, exogenous NAA induces substantial changes in maize roots, with the phenylpropanoid biosynthesis pathway playing a crucial role in the maize root's response to exogenous NAA regulation under K-deficiency.

Contrasting depth‐related fine root plastic responses to soil warming in a subtropical Chinese fir plantation

Abstract Warming‐induced soil drought, especially in topsoil, may enlarge the spatial mismatch between nutrients and water along the soil profile, which impedes the uptake of not only water but also nutrients by trees. Therefore, coordinating the acquisition of soil water and nutrients along the soil profile is an important strategy for trees to cope with global warming. This study examined soil depth‐related changes in nutrient concentrations, biomass and morphology of fine roots in a Chinese fir plantation after 3 years of large‐scale manipulative soil warming. Soil warming (ambient +4°C) increased fine root nitrogen (N) concentrations but decreased fine root phosphorus (P) concentrations across soil depths. Warming did not affect total fine root biomass and its vertical distribution. At the 0–10 cm depth, warming increased specific root length (SRL), specific root area (SRA), fine root diameter (RD) and root length density (RLD) but reduced root tissue density (RTD). In the 40–60 cm layer, warming reduced RD, SRL and RLD while increasing RTD mainly for roots of the 1–2 mm diameter class. Synthesis. We concluded that roots of Chinese fir plantations could adapt to warming‐induced moderate water stress through contrasting depth‐related root morphological adjustments, probably to optimize the acquisition of both soil water and nutrients. The results of this study are crucial for understanding the adaptation strategies of subtropical forests under future climate conditions.

Photovoltaic systems promote grassland restoration by coordinating water and nutrient uptake, transport and utilization

The extensive use of fossil fuels puts ecological and economic coordinated development at risk. Photovoltaic systems relieve the pressure of resource extraction and energy generation on climate change, and their installation and module operation affect vegetation productivity and grassland restoration by changing the microenvironment and ecosystem processes. However, it is still unclear whether plants adapt to these changes in photovoltaic systems to sustain their growth. Here, combined stable isotope techniques with plant traits, plant adaptations to photovoltaic systems at different scales were analyzed from the perspectives of water and nutrient sources, uptake, transport, and utilization. The results showed that photovoltaic systems increased water uptake by the dominant species Leymus chinensis from the top 10 cm of the soil and the aboveground biomass. This was associated with strong plasticity of roots and conduction tissues, which improved resource uptake from the fertile surface soil and transport within the plant, and promoted photosynthesis and leaf water loss by inducing stomatal opening. Different from fixed photovoltaic systems, tracking photovoltaic systems improved ecosystem water use efficiency and surface soil nutrient availability by reducing soil temperature. Tilting tracking photovoltaic systems especially promoted biomass accumulation and grassland restoration. The study suggested that photovoltaic systems promoted vegetation restoration of grassland ecosystem in semi-arid region through the water and nutrient coordination and the carbon-water coupling, and provides a solution for reasonable planning of photovoltaic industry and sustainable socio-economic development.

Changes in the degree of lateral root trait plasticity and trade-offs of maize under long-term no tillage.

While no tillage (NT) can significantly influence soil structure stratification compared to conventional tillage (CT), a comprehensive understanding of the degree of root trait plasticity and trade-offs of lateral roots of crops at various growth stages along a deep soil profile in response to NT remains elusive. This knowledge gap is important for understanding soil resource acquisition strategies and yield of crops. We systematically investigated the traits of lateral roots at jointing and flowering stages in a long-term (12 years) experiment in Northeast China where maize (Zea mays) has been continuously planted under CT and NT with or without maize residue mulch on soil surface. We also measured soil penetration resistance and bulk density. Soil penetration resistance was reduced at the jointing stage, and was increased at the flowering stage under NT especially at a depth of 10 - 40 cm. Root length density decreased under NT across the two growth stages by on average 22%. In contrast, specific root length and diameter showed greater plasticity, ranging from -14% to 20% and from -11% to 8%, respectively, relative to those under CT. These responses could be attributed to changes in root length proportions with different diameters associated with differences in soil penetration resistance between tillage practices. The negative relationships between root traits were stronger under CT than NT, and became weaker from the jointing stage to the flowering stage. To the best of our knowledge, for the first time, our study provides empirical evidence for pivotal root trait plasticity and trade-offs across growth stages as key indicators of changes in soil structure and resources in response to NT. These insights contribute to a better understanding of soil resource acquisition strategies of crops under NT.

More N fertilizer, more maize, and less alfalfa: maize benefits from its higher N uptake per unit root length.

Root plasticity is fundamental to soil nutrient acquisition and maximizing production. Different soil nitrogen (N) levels affect root development, aboveground dry matter accumulation, and N uptake. This phenotypic plasticity is well documented for single plants and specific monocultures but is much less understood in intercrops in which species compete for the available nutrients. Consequently, the study tested whether the plasticity of plant roots, biomass and N accumulation under different N levels in maize/alfalfa intercropping systems differs quantitatively. Maize and alfalfa were intercropped for two consecutive years in large soil-filled rhizoboxes and fertilized with 6 different levels of N fertilizer (0, 75, 150, 225, 270, and 300 kg ha-1). Root length, root surface area, specific root length, N uptake and yield were all increased in maize with increasing fertilizer level, whereas higher N rates were supraoptimal. Alfalfa had an optimal N rate of 75-150 kg ha-1, likely because the competition from maize became more severe at higher rates. Maize responded more strongly to the fertilizer treatment in the second year when the alfalfa biomass was much larger. N fertilization contributes more to maize than alfalfa growth via root plasticity responses. Our results suggest that farmers can maximize intercropping yield and economic return by optimizing N fertilizer management.

Ethylene Modulates Rice Root Plasticity under Abiotic Stresses

Plants live in constantly changing environments that are often unfavorable or stressful. Root development strongly affects plant growth and productivity, and the developmental plasticity of roots helps plants to survive under abiotic stress conditions. This review summarizes the progress being made in understanding the regulation of the phtyohormone ethylene in rice root development in response to abiotic stresses, highlighting the complexity associated with the integration of ethylene synthesis and signaling in root development under adverse environments. Understanding the molecular mechanisms of ethylene in regulating root architecture and response to environmental signals can contribute to the genetic improvement of crop root systems, enhancing their adaptation to stressful environmental conditions.

Response of yield, root traits and plasticity of nitrogen-efficient cultivars of drip-irrigated rice to a nitrogen environment

The response of drip-irrigated rice physiological traits to water and fertilisers has been widely studied. However, the responses of yield, root traits and their plasticity to the nitrogen environment in different nitrogen-efficient cultivars are not fully understood. An experiment was conducted from 2020-2022 with high nitrogen efficient (high-NUE) cultivars (T-43) and low-NUE cultivars (LX-3), and four nitrogen levels (0, 150, 300, and 450 kg ha-1) under drip irrigation in large fields were used. The aim was to study the relationship between root morphology, conformation, biomass, and endogenous hormone content and yield and nitrogen use efficiency. The results showed the following: 1) Under the same N application rate, compared with LX-3, T-43’s yield, N partial factor productivity (PFP), fine root length density (FRLD), shoot dry weight (SDW), root indole-3-acetic acid (IAA), and root zeatin and zeatin riboside (Z+ZR) were significantly increased by 11.4-18.9%, 11.3-13.5%, 11.6-15.7%, 9.9-31.1%, 6.1-48.1%, and 22.8-73.6%, respectively, while the root-shoot ratio (RSR) and root abscisic acid (ABA) were significantly decreased (P<0.05). 2) Nitrogen significantly increased rice root morphological indexes and endogenous hormone contents (P<0.05). Compared to N0, yield, root length density (RLD), surface area density (SAD), Root volume density (RVD), and root endogenous hormones (IAA, Z+ZR) were significantly increased in the 2 cultivars under N2 by 61.6-71.6%, 64.2-74.0%, 69.9-105.6%, 6.67-9.91%, 54.0-67.8%, and 51.4-58.9%, respectively. Compared with N3, the PFP and N agronomic efficiency (NAE) of nitrogen fertiliser under N2 increased by 52.3-62.4% and 39.2-63.0%, respectively. 3) The response of root trait plasticity to the N environment significantly differed (P<0.05). Compared with LX-3, T-43 showed a longer root length and larger specific surface area, which is a strategy for adapting to changes in the nutrient environment. For rice cultivars with high-NUE, the root-shoot ratio was optimised by increasing the FRLD, root distribution in upper soil layers, and root endogenous hormones (IAA, Z+ZR) under suitable nitrogen conditions (N2). An efficient nutrient acquisition strategy can occur through root plasticity, leading to increased yield and NUE.

Zoom-in to molecular mechanisms underlying root growth and function under heterogeneous soil environment and abiotic stresses.

The review describes tissue-specific and non-cell autonomous molecular responses regulating the root system architecture and function in plants. Phenotypic plasticity of roots relies on specific molecular and tissue specific responses towards local and microscale heterogeneity in edaphic factors. Unlike gravitropism, hydrotropism in Arabidopsis is regulated by MIZU KUSSIE1 (MIZ1)-dependent asymmetric distribution of cytokinin and activation of Arabidopsis response regulators, ARR16 and ARR17 on the lower water potential side of the root leading to higher cell division and root bending. The cortex specific role of Abscisic acid (ABA)-activated SNF1-related protein kinase 2.2 (SnRK2.2) and MIZ1 in elongation zone is emerging for hydrotropic curvature. Halotropism involves clathrin-mediated internalization of PIN FORMED 2 (PIN2) proteins at the side facing higher salt concentration in the root tip, and ABA-activated SnRK2.6 mediated phosphorylation of cortical microtubule-associated protein Spiral2-like (SP2L) in the root transition zone, which results in anisotropic cell expansion and root bending away from higher salt. In hydropatterning, Indole-3-acetic acid 3 (IAA3) interacts with SUMOylated-ARF7 (Auxin response factor 7) and prevents expression of Lateral organ boundaries-domain 16 (LBD16) in air-side of the root, while on wet side of the root, IAA3 cannot repress the non-SUMOylated-ARF7 thereby leading to LBD16 expression and lateral root development. In root vasculature, ABA induces expression of microRNA165/microRNA166 in endodermis, which moves into the stele to target class III Homeodomain leucine zipper protein (HD-ZIP III) mRNA in non-cell autonomous manner. The bidirectional gradient of microRNA165/6 and HD-ZIP III mRNA regulates xylem patterning under stress. Understanding the tissue specific molecular mechanisms regulating the root responses under heterogeneous and stress environments will help in designing climate-resilient crops.

Root plasticity benefits a global invasive species in eutrophic coastal wetlands

Abstract Invasive species usually benefit more than native species from increases in nutrient availability. Phenotypic plasticity in above‐ground traits has often been used to explain the superiority of invasive species in response to increased nutrient availability. However, it remains largely unclear whether and how root trait plasticity predicts the ascendancy of invasive plants following nutrient enrichment. Using a 3‐year field nitrogen (N) enrichment experiment, we evaluated the effect of N enrichment on the root traits and growth performance of a globally invasive cordgrass, Spartina alterniflora, and a co‐occurring native plant, Phragmites australis. We found that S. alterniflora exhibited high plasticity in root traits in response to N enrichment, whereas the root traits of P. australis largely remained unresponsive to fertilization. Specifically, in response to N enrichment, S. alterniflora decreased soil exploitation with a lower length ratio of lateral to adventitious roots. However, the root traits of S. alterniflora shifted to be more acquisitive under N enrichment with higher root N concentrations and lower root tissue density. Moreover, there were a series of anatomical adjustments in the adventitious roots of S. alterniflora in response to N enrichment, such as a thicker diameter, lower living cortex‐to‐stele ratio and higher xylem‐to‐root area ratio. These plastic adjustments in root traits jointly resulted in fast nutrient uptake and transportation in S. alterniflora, boosting its above‐ground productivity under fertile N conditions. Our study demonstrated that greater plasticity in root traits enables a globally successful invasive species to take advantages of increased nutrient availability, potentially increasing its invasiveness. We suggest that consideration of root traits can improve our understanding of below‐ground mechanisms underlying invasion under global nutrient enrichment. Read the free Plain Language Summary for this article on the Journal blog.

Maize, wheat, and soybean root traits depend upon soil phosphorus fertility and mycorrhizal status.

Strong effects of plant identity, soil nutrient availability or mycorrhizal fungi on root traits have been well documented, but their interactive influences on root traits are still poorly understood. Here, three crop species (maize, wheat and soybean) were grown under four phosphorus (P) addition levels (0, 20, 40 and 60mg P kg-1 dry soil), and plants were inoculated with or without five combined arbuscular mycorrhizal fungal (AMF) species. Plant biomass, nutrient contents, root traits (including total root length, average root diameter, specific root length and root tissue density) and plants' mycorrhizal responses were measured. Crop species, P level, AMF, and their interactions strongly affected plant biomass and root traits. P fertilization promoted plant growth but reduced mycorrhizal benefits on plant biomass and nutrient uptake. Root traits of maize were sensitive to P addition only under the non-mycorrhizal condition, whilst most root traits of soybean and wheat plants were responsive to mycorrhizal inoculation but not P addition. Mycorrhizal colonization reduced the root plasticity in response to P fertility for maize but not for wheat or soybean. This study highlights the importance of soil nutrient fertility and mycorrhizal symbiosis in influencing root traits.

Influence of Incremental Short Term Salt Stress at the Seedling Stage on Root Plasticity, Shoot Thermal Profile and Ion Homeostasis in Contrasting Wheat Genotypes

Understanding the component traits determining salt stress tolerance is a major breeding target in wheat. The lack of genetic resources suited to salt-affected regions and the complexity of the traits involved impede progress in breeding salt-tolerant wheat varieties. This study was conducted with four bread wheats, namely (Triticum aestivum) Kharchia-65 (K-65), BT-Schomburgk (BTS), HD-2687, and HD-3298. Treatments were imposed on plants with varying electrical conductivity (control, 5 dS m−1, 10 dS m−1, and 15 dS m−1) with a combination of three different salts NaCl, CaCl2·2H2O, and Na2SO4. We evaluated variations in root system architecture, canopy temperature (depicted as a thermal image), reactive oxygen species (ROS) homeostasis, and leaf stomatal density in response to incremental doses of salt stress in a hydroponic experiment. As the plants were sampled after short-term exposure to stress (within 3 weeks of stress imposition), the plants were expected to be in a quiescent state. Due to the osmotic effect, the growth of the plants was compromised, and the associated decrease in stomatal conductance increased the canopy temperature. ROS accumulation and antioxidant enzyme activity did not follow a definite pattern. The antioxidant system’s tolerance to ROS comes into action much later in the tolerance mechanism. That could probably be the reason behind the varied response in ROS accumulation and antioxidant enzymes after short-term exposure to salt stress. Thermal images could effectively differentiate between salt-tolerant (K65) and sensitive (HD2687) genotypes. The variation in Na+/K+ ratio also suggested a genotypic variation in salt tolerance. The genotypes of K-65 maintained a better root system, while HD2687 showed severe reduction in root biomass and other root traits under salt stress. The PCA data also point out genotypic variation in lateral and main root traits in response to different salt stress levels. For salt tolerance in wheat, the main contributing root traits were total root length, total surface area, total root volume, tips, and other main, lateral root traits. The idea of differential control of RSA dynamics is novel and can be further explored to understand natural variation in salt stress tolerance.

Improving rice nitrogen-use efficiency by modulating a novel monouniquitination machinery for optimal root plasticity response to nitrogen.

Plant nitrogen (N)-use efficiency (NUE) is largely determined by the ability of root to take up external N sources, whose availability and distribution in turn trigger the modification of root system architecture (RSA) for N foraging. Therefore, improving N-responsive reshaping of RSA for optimal N absorption is a major target for developing crops with high NUE. In this study, we identified RNR10 (REGULATOR OF N-RESPONSIVE RSA ON CHROMOSOME 10) as the causal gene that underlies the significantly different root developmental plasticity in response to changes in N level exhibited by the indica (Xian) and japonica (Geng) subspecies of rice. RNR10 encodes an F-box protein that interacts with a negative regulator of auxin biosynthesis, DNR1 (DULL NITROGEN RESPONSE1). Interestingly, RNR10 monoubiquitinates DNR1 and inhibits its degradation, thus antagonizing auxin accumulation, which results in reduced root responsivity to N and nitrate (NO3-) uptake. Therefore, modulating the RNR10-DNR1-auxin module provides a novel strategy for coordinating a desirable RSA and enhanced N acquisition for future sustainable agriculture.

Constitutive basis of root system architecture: uncovering a promising trait for breeding nutrient- and drought-resilient crops

Root system architecture (RSA) plays a pivotal role in efficient uptake of essential nutrients, such as phosphorous (P), nitrogen (N), and water. In soils with heterogeneous nutrient distribution, root plasticity can optimize acquisition and plant growth. Here, we present evidence that a constitutive RSA can confer benefits for sorghum grown under both sufficient and limiting growth conditions. Our studies, using P efficient SC103 and inefficient BTx635 sorghum cultivars, identified significant differences in root traits, with SC103 developing a larger root system with more and longer lateral roots, and enhanced shoot biomass, under both nutrient sufficient and deficient conditions. In addition to this constitutive attribute, under P deficiency, both cultivars exhibited an initial increase in lateral root development; however, SC103 still maintained the larger root biomass. Although N deficiency and drought stress inhibited both root and shoot growth, for both sorghum cultivars, SC103 again maintained the better performance. These findings reveal that SC103, a P efficient sorghum cultivar, also exhibited enhanced growth performance under N deficiency and drought. Our results provide evidence that this constitutive nature of RSA can provide an avenue for breeding nutrient- and drought-resilient crops.