Importance of individual root traits to understand crop root system in agronomic and environmental contexts

Response of submerged macrophytes of different growth forms to multiple sediment remediation measures for hardened sediment

Climate change and intensified human activities have disrupted the natural hydrological regime and rhythm of river-connected lakes, extending the dry season, increasing water loss, and exposing previously submerged lake floors. This exposure has led to significant sediment hardening, which directly impacts submerged macrophytes. However, strategies to mitigate the negative effects of hardened sediments and promote the growth and development of submerged macrophytes remain largely unexplored. In this study, we selected typical hardened sediment from Dongting Lake to investigate the response of different growth forms of submerged macrophytes to multiple sediment remediation measures (loosening and litter addition) using a mesocosm experiment. The results indicated that loosening alone uniformly benefited all submerged macrophytes by increasing total biomass, relative growth rate (RGR), and the root/shoot ratio. Additionally, loosening altered the root traits of submerged macrophytes, promoting maximum root length (MRL) while reducing average root diameter (ARD). Moreover, different submerged macrophytes exhibited species-specific responses to the combination of loosening and litter addition. Notably, the combination of loosening and adding Miscanthus lutarioriparius litter had an antagonistic effect on the growth of Potamogeton wrightii and Myriophyllum spicatum. The response of functional traits of submerged macrophytes with similar growth forms to the same treatment was consistent. Our findings suggest that future sediment remediation efforts should consider matching specific treatments with the growth forms of submerged macrophytes to achieve optimal outcomes.

Modeling the effects of strigolactone levels on maize root system architecture

Maize is the most in-demand staple crop globally. Its production relies strongly on the use of fertilizers for the supply of nitrogen, phosphorus, and potassium, which the plant absorbs through its roots, together with water. The architecture of maize roots is determinant in modulating how the plant interacts with the microbiome and extracts nutrients and water from the soil. As such, attempts to use synthetic biology and modulate that architecture to make the plant more resilient to drought and parasitic plants are underway. These attempts often try to modulate the biosynthesis of hormones that determine root architecture and growth. Experiments are laborious and time-consuming, creating the need for simulation platforms that can integrate metabolic models and 3D root growth models and predict the effects of synthetic biology interventions on both, hormone levels and root system architectures. Here, we present an example of such a platform that is built using Mathematica. First, we develop a root model, and use it to simulate the growth of many unique 3D maize root system architectures (RSAs). Then, we couple this model to a metabolic model that simulates the biosynthesis of strigolactones, hormones that modulate root growth and development. The coupling allows us to simulate the effect of changing strigolactone levels on the architecture of the roots. We then integrate the two models in a simulation platform, where we also add the functionality to analyze the effect of strigolactone levels on root phenotype. Finally, using in silico experiments, we show that our models can reproduce both the phenotype of wild type maize, and the effect that varying strigolactone levels have on changing the architecture of maize roots.

Effect of salt, alkali and combined stresses on root system architecture and ion profiling in a diverse panel of oat (Avena spp.)

The co-occurrence of salinisation and alkalisation is quite frequent in problematic soils and poses an immediate threat to food, feed and nutritional security. In the present study, root system architectural traits (RSAs) and ion profiling were evaluated in 21 genotypes of Avena species to understand the effect of salinity-alkalinity stress. The oat genotypes were grown on germination paper and 5-day-old seedlings were transferred to a hydroponic system for up to 30days. These seedlings were subjected to seven treatments: T0 , treatment control (Hoagland solution); T1 , moderate salinity (50mM); T2 , high salinity (100mM); T3 , moderate alkalinity (15mM); T4 , high alkalinity (30mM); T5 , combined moderate salinity-alkalinity (50mM+15mM); and T6 , combined high salinity-alkalinity (100mM and 30mM) by using NaCl+Na2 SO4 (saline) and NaHCO3 +Na2 CO3 (alkaline) salts equivalently. The root traits, such as total root area (TRA), total root length (TRL), total root diameter (TRD), total root volume (TRV), root tips (RT), root segments (RS), root fork (RF) and root biomass (RB) were found to be statistically significant (P + and K+ content analysis in root and shoot tissues revealed the ion homeostasis capacity of different Avena accessions under stress treatments. Principal component analysis (PCA) covered almost 83.0% of genetic variation and revealed that the sharing of TRA, RT, RS and RF traits was significantly high. Biplot analysis showed a highly significant correlation matrix (P <0.01) between the pairs of RT and RS, TRL and RS, and RT and RF. Based on PCA ranking and relative value for stress tolerance, IG-20-1183, IG-20-894, IG-20-718 and IG-20-425 expressed tolerance to salinity (T2), IG-20-425 (alkalinity; T4) and IG-20-1183, IG-20-894 and IG-20-1004 were tolerant to salt-alkali treatment (T6). Multi-trait stability index (MTSI) analysis identified three stable oat genotypes (IG-20-714, IG-20-894 and IG-20-425) under multiple environments and these lines can be used in salinity-alkalinity affected areas after yield trials or as donor lines for combined stresses in future breeding programs.

Maximizing trace metal phytoextraction through planting methods: Role of rhizosphere fertility and microbial activities

Brownfields are a widespread problem in the world. The poor quality of these soils and the potential presence of contaminants can pose a significant threat to plant establishment and growth. However, it may be possible to improve their establishment with an appropriate agricultural practice. In this paper, the effects of two common planting strategies, seeding and transplanting, on the establishment and growth of the hyperaccumulator species Noccaea caerulescens and on its phytoextraction capacity were investigated. A field experiment was conducted by direct sowing of N. caerulescens seeds on a plot of contaminated Technosols in Jeandelaincourt, France. At the same time, seeds were sown on potting soil under controlled conditions. One month later, the seedlings were transplanted to the field. One year later, the results showed that transplanting improved the establishment and growth of N. caerulescens. This was due to a decrease in soil pH in the rhizosphere, which subsequently increased nutrient availability. This change in rhizosphere properties also appeared to be the key that improved microbial activities in the rhizosphere soil of transplanted plants. The observed improvement in both rhizosphere nutrient availability and microbial activities, in turn, increased auxin concentrations in the rhizosphere and consequently a more developed root system was observed in the transplanted plants. Furthermore, the Cd and Zn phytoextraction yield of transplanted plants is 2.5 and 5 times higher, respectively, than that of sown plants. In conclusion, N. caerulescens transplantation on contaminated sites seems to be an adequate strategy to improve plant growth and enhance trace metal phytoextraction.

The role of root size and root efficiency in grain production, and water-and nitrogen-use efficiency in wheat

BACKGROUND

The root system is the major plant organ involved in water and nutrient acquisition, influencing plant growth and productivity. However, the relative importance of root size and uptake efficiency remains undetermined. A pot experiment was conducted using two wheat varieties with different root sizes to evaluate their capacity for water and nitrogen (N) uptake and their effects on grain production, water-use efficiency (WUE), and N-use efficiency (NUE) under two water treatments combined with three N levels.

RESULTS

The leaf water potential and root exudates of changhan58 (CH, small root variety) were higher or similar to those of changwu134 (CW, large root variety) under water/N treatment combinations, indicating that small roots can transport enough water to above the ground. The addition of N improved plant growth, photosynthetic traits, and WUE significantly. There were no significant differences in WUE or grain production between the two cultivars under well-watered conditions. However, they were significantly higher in CH than in CW under water deficit stress. Nitrogen uptake per unit root dry weight, glutaminase, and nitrate reductase activities were significantly higher in CH than in CW, regardless of moisture conditions. Root biomass was positively correlated with evapotranspiration, while the root/shoot ratio was negatively correlated with WUE (P < 0.05) but not with NUE.

CONCLUSION

In a pot experiment, water and N uptake were more strongly associated with resource uptake availability than root size. This may provide guidance in wheat breeding programs for drought-prone regions. © 2023 Society of Chemical Industry.

Plasticity of root hair and rhizosheath traits and their relationship to phosphorus uptake in sorghum

Sorghum is an essential crop for resilient and adaptive responses to climate change. The root systems of crop plants significantly contribute to the tolerance of abiotic stresses. There is little information on sorghum genotypes' root systems and plasticity to external P supply. In this paper, we investigated the variations in root systems, as well as the responses, trait relationships, and plasticity of two sorghum genotypes (Naga Red and Naga White), popularly grown in Ghana, to five external P concentrations ([P]ext): 0, 100, 200, 300, and 400 mg P kg-1 soil. Sorghum plants were grown in greenhouse pots and harvested for root trait measurements at the five-leaf and growing point differentiation (GPD) developmental stages. The plants were responsive to [P]ext and formed rhizosheaths. The two genotypes showed similar characteristics for most of the traits measured but differed significantly in total and lateral root lengths in favor of the red genotype. For example, at the five-leaf growth stage, the lateral root length of the red and white genotypes was 22.8 and 16.2 cm, respectively, but 124 and 88.9 cm, at the GPD stage. The responses and plasticity of the root system traits, including rhizosheath, to [P]ext were more prominent, positive, and linear at the five-leaf stage than at the GPD growth stage. At the five-leaf growth stage, total root length increased by about 2.5-fold with increasing [P]ext compared to the unamended soil. At the GPD stage, however, total root length decreased by about 1.83-fold as [P]ext increased compared to the unamended soil. Specific rhizosheath weight correlated with RHD, albeit weakly, and together explained up to 59% of the variation in tissue P. Root hair density was more responsive to P supply than root hair length and showed a similar total and lateral root length pattern. Most desirable responses to P occurred at a rate of 200-300 mg P kg-1 soil. It is concluded that sorghum would form rhizosheath, and [P]ext could be critical for the early vigorous growth of sorghum's responsive root and shoot traits. Beyond the early days of development, additional P application might be necessary to sustain the responses and plasticity observed during the early growth period, but this requires further investigation, potentially under field conditions.

Rock, scissors, paper: How RNA structure informs function

RNA can fold back on itself to adopt a wide range of structures. These range from relatively simple hairpins to intricate 3D folds and can be accompanied by regulatory interactions with both metabolites and macromolecules. The last 50 yr have witnessed elucidation of an astonishing array of RNA structures including transfer RNAs, ribozymes, riboswitches, the ribosome, the spliceosome, and most recently entire RNA structuromes. These advances in RNA structural biology have deepened insight into fundamental biological processes including gene editing, transcription, translation, and structure-based detection and response to temperature and other environmental signals. These discoveries reveal that RNA can be relatively static, like a rock; that it can have catalytic functions of cutting bonds, like scissors; and that it can adopt myriad functional shapes, like paper. We relate these extraordinary discoveries in the biology of RNA structure to the plant way of life. We trace plant-specific discovery of ribozymes and riboswitches, alternative splicing, organellar ribosomes, thermometers, whole-transcriptome structuromes and pan-structuromes, and conclude that plants have a special set of RNA structures that confer unique types of gene regulation. We finish with a consideration of future directions for the RNA structure-function field.

The wheat basic helix-loop-helix gene TabHLH123 positively modulates the formation of crown roots and is associated with plant height and 1000-grain weight under various conditions

Crown roots are the main components of the fibrous root system in cereal crops and play critical roles in plant adaptation; however, the molecular mechanisms underlying their formation in wheat (Triticum aestivum) have not been fully elucidated. In this study, we identified a wheat basic helix-loop-helix (bHLH) protein, TabHLH123, that interacts with the essential regulator of crown root initiation, MORE ROOT in wheat (TaMOR). TabHLH123 is expressed highly in shoot bases and roots. Ectopic expression of TabHLH123 in rice resulted in more roots compared with the wild type. TabHLH123 regulates the expression of genes controlling crown-root development and auxin metabolism, responses, and transport. In addition, we analysed the nucleotide sequence polymorphisms of TabHLH123s in the wheat genome and identified a superior haplotype, TabHLH123-6B, that is associated with high root dry weight and 1000-grain weight, and short plant height. Our study reveals the role of TabHLH123 in controlling the formation of crown roots and provides beneficial insights for molecular marker-assisted breeding in wheat.

The Higher Water Absorption Capacity of Small Root System Improved the Yield and Water Use Efficiency of Maize

The root system in plants absorbs water and minerals. However, the relationship among root size, yield, and water use efficiency (WUE) is controversial. Two pot experiments were conducted to explore these relationships by using two maize varieties with contrasting root sizes and reducing the root-shoot ratio (R/S) through root pruning to eliminate genotypic effects. Maize plants were grown in an open rainout shelter under both water-sufficient and deficient conditions. Yield-related parameters, root hydraulic conductivity (Lpr), and WUE were determined. The results showed that the small root variety (XY) has a higher yield and WUE compared to large root variety (QL) under both soil moisture conditions, likely related to the higher Lpr of XY. XY also had a higher leaf water potential than QL under drought stress, indicating that small root system could provide enough water to the shoot. Further pot experiment showed that both small and large root pruning on QL (cut off about 1/5 roots, RP1; and cut off about 1/3 roots, RP2, respectively) improved WUE and Lpr, and the RP1 yield increased by 12.9% compared to the control under well-watered conditions. Root pruning decreased transpiration and increased photosynthesis. Thus, this study reveals that it is possible to increase water absorption, yield, and WUE by reducing R/S in modern maize varieties, which may be important for the future breeding of new cultivars suitable for arid regions.

Spatial-Temporal Distribution of Allelopathic Rice Roots in Paddy Soil and Its Impact on Weed-Suppressive Activity at the Seedling Stages

BACKGROUND

Allelochemicals secreted by allelopathic rice roots are transmitted to the receptor rhizosphere through the soil medium to inhibit the growth of the surrounding weeds. This research aimed to explore the relationships between the spatial-temporal distribution of rice roots in soil and weed-suppression ability at its seedling stage.

RESULTS

This study first examined the root distribution of three rice cultivars in paddy soil in both vertical and horizontal directions at 3-6 leaf stage. Then, an experiment using rice-barnyardgrass mixed culture was conducted to analyze the allelopathic potential and allelochemical content secreted by rice roots in different lateral soil layers. The results showed that allelopathic rice had a smaller root diameter and larger root length density, root surface area density, and root dry weight density than those of non-allelopathic rice, in the top 5 cm at 5- and 6-leaf stages. In particular, there were significant differences in root distribution at the horizontal distance of 6-12 cm. Besides, allelopathic rice significantly inhibited the above-ground growth of barnyardgrass co-cultured at 12 cm lateral distance in situ, and the content of benzoic acid derivatives in allelopathic rice in a 6-12 cm soil circle was higher than that observed at 0-6 cm distance. Moreover, correlation analysis confirmed that the distribution of roots in the horizontal distance was significantly correlated with weed inhibition effect and allelochemical content.

CONCLUSION

These results implied that spatial distribution of allelopathic rice roots in paddy soil, particularly at the lateral distance, appears to have important impact on its weed-suppressive activity at the seedling stage, suggesting that modifying root distribution in soil may be a novel method to strengthen the ability of rice seedlings to resist paddy weeds.