The first intron of ARF7 is required for expression in root tips.

Auxin regulates plant growth and development through the transcription factors of the AUXIN RESPONSE FACTOR (ARF) gene family. ARF7 is one of five activators that bind DNA and elicit downstream transcriptional responses. In roots, ARF7 regulates growth, gravitropism and redundantly with ARF19, lateral root organogenesis. In this study we analyzed ARF7 cis-regulation, using different non-coding sequences of the ARF7 locus to drive GFP. We show that constructs containing the first intron led to increased signal in the root tip. Although bioinformatics analyses predicted several transcription factor binding sites in the first intron, we were unable to significantly alter expression of GFP in the root by mutating these. We instead observed the intronic sequences needed to be present within the transcribed sequences to drive expression in the root meristem. These data support a mechanism by which intron-mediated enhancement regulates the tissue specific expression of ARF7 in the root meristem.

Integrating cryo-OrbiSIMS with computational modelling and metadynamics simulations enhances RNA structure prediction at atomic resolution.

The 3D architecture of RNAs governs their molecular interactions, chemical reactions, and biological functions. However, a large number of RNAs and their protein complexes remain poorly understood due to the limitations of conventional structural biology techniques in deciphering their complex structures and dynamic interactions. To address this limitation, we have benchmarked an integrated approach that combines cryogenic OrbiSIMS, a state-of-the-art solid-state mass spectrometry technique, with computational methods for modelling RNA structures at atomic resolution with enhanced precision. Furthermore, using 7SK RNP as a test case, we have successfully determined the full 3D structure of a native RNA in its apo, native and disease-remodelled states, which offers insights into the structural interactions and plasticity of the 7SK complex within these states. Overall, our study establishes cryo-OrbiSIMS as a valuable tool in the field of RNA structural biology as it enables the study of challenging, native RNA systems.

The auxin efflux carrier PIN1a regulates vascular patterning in cereal roots.

Barley (Hordeum vulgare) is an important global cereal crop and a model in genetic studies. Despite advances in characterising barley genomic resources, few mutant studies have identified genes controlling root architecture and anatomy, which plays a critical role in capturing soil resources. Our phenotypic screening of a TILLING mutant collection identified line TM5992 exhibiting a short-root phenotype compared with wild-type (WT) Morex background. Outcrossing TM5992 with barley variety Proctor and subsequent SNP array-based bulk segregant analysis, fine mapped the mutation to a cM scale. Exome sequencing pinpointed a mutation in the candidate gene HvPIN1a, further confirming this by analysing independent mutant alleles. Detailed analysis of root growth and anatomy in Hvpin1a mutant alleles exhibited a slower growth rate, shorter apical meristem and striking vascular patterning defects compared to WT. Expression and mutant analyses of PIN1 members in the closely related cereal brachypodium (Brachypodium distachyon) revealed that BdPIN1a and BdPIN1b were redundantly expressed in root vascular tissues but only Bdpin1a mutant allele displayed root vascular defects similar to Hvpin1a. We conclude that barley PIN1 genes have sub-functionalised in cereals, compared to Arabidopsis (Arabidopsis thaliana), where PIN1a sequences control root vascular patterning.

A genomic toolkit for winged bean Psophocarpus tetragonolobus.

A sustainable supply of plant protein is critical for future generations and needs to be achieved while reducing green house gas emissions from agriculture and increasing agricultural resilience in the face of climate volatility. Agricultural diversification with more nutrient-rich and stress tolerant crops could provide the solution. However, this is often hampered by the limited availability of genomic resources and the lack of understanding of the genetic structure of breeding germplasm and the inheritance of important traits. One such crop with potential is winged bean (Psophocarpus tetragonolobus), a high seed protein tropical legume which has been termed 'the soybean for the tropics'. Here, we present a chromosome level winged bean genome assembly, an investigation of the genetic diversity of 130 worldwide accessions, together with two linked genetic maps and a trait QTL analysis (and expression studies) for regions of the genome with desirable ideotype traits for breeding, namely architecture, protein content and phytonutrients.

Ethylene regulates auxin-mediated root gravitropic machinery and controls root angle in cereal crops.

Root angle is a critical factor in optimizing the acquisition of essential resources from different soil depths. The regulation of root angle relies on the auxin-mediated root gravitropism machinery. While the influence of ethylene on auxin levels is known, its specific role in governing root gravitropism and angle remains uncertain, particularly when Arabidopsis (Arabidopsis thaliana) core ethylene signaling mutants show no gravitropic defects. Our research, focusing on rice (Oryza sativa L.) and maize (Zea mays), clearly reveals the involvement of ethylene in root angle regulation in cereal crops through the modulation of auxin biosynthesis and the root gravitropism machinery. We elucidated the molecular components by which ethylene exerts its regulatory effect on auxin biosynthesis to control root gravitropism machinery. The ethylene-insensitive mutants ethylene insensitive2 (osein2) and ethylene insensitive like1 (oseil1), exhibited substantially shallower crown root angle compared to the wild type. Gravitropism assays revealed reduced root gravitropic response in these mutants. Hormone profiling analysis confirmed decreased auxin levels in the root tips of the osein2 mutant, and exogenous auxin (NAA) application rescued root gravitropism in both ethylene-insensitive mutants. Additionally, the auxin biosynthetic mutant mao hu zi10 (mhz10)/tryptophan aminotransferase2 (ostar2) showed impaired gravitropic response and shallow crown root angle phenotypes. Similarly, maize ethylene-insensitive mutants (zmein2) exhibited defective gravitropism and root angle phenotypes. In conclusion, our study highlights that ethylene controls the auxin-dependent root gravitropism machinery to regulate root angle in rice and maize, revealing a functional divergence in ethylene signaling between Arabidopsis and cereal crops. These findings contribute to a better understanding of root angle regulation and have implications for improving resource acquisition in agricultural systems.

Genetic regulation of the root angle in cereals.

The root angle plays a critical role in efficiently capturing nutrients and water from different soil layers. Steeper root angles enable access to mobile water and nitrogen from deeper soil layers, whereas shallow root angles facilitate the capture of immobile phosphorus from the topsoil. Thus, understanding the genetic regulation of the root angle is crucial for breeding crop varieties that can efficiently capture resources and enhance yield. Moreover, this understanding can contribute to developing varieties that effectively sequester carbon in deeper soil layers, supporting global carbon mitigation efforts. Here we review and consolidate significant recent discoveries regarding the molecular components controlling root angle in cereal crop species and outline the remaining research gaps in this field.

Challenges facing sustainable protein production: Opportunities for cereals.

Rising demands for protein worldwide are likely to drive increases in livestock production, as meat provides ∼40% of dietary protein. This will come at a significant environmental cost, and a shift toward plant-based protein sources would therefore provide major benefits. While legumes provide substantial amounts of plant-based protein, cereals are the major constituents of global foods, with wheat alone accounting for 15-20% of the required dietary protein intake. Improvement of protein content in wheat is limited by phenotyping challenges, lack of genetic potential of modern germplasms, negative yield trade-offs, and environmental costs of nitrogen fertilizers. Presenting wheat as a case study, we discuss how increasing protein content in cereals through a revised breeding strategy combined with robust phenotyping could ensure a sustainable protein supply while minimizing the environmental impact of nitrogen fertilizer.

Loss of ancestral function in duckweed roots is accompanied by progressive anatomical reduction and a re-distribution of nutrient transporters.

Organ loss occurs frequently during plant and animal evolution. Sometimes, non-functional organs are retained through evolution. Vestigial organs are defined as genetically determined structures that have lost their ancestral (or salient) function.1,2,3 Duckweeds, an aquatic monocot family, exhibit both these characteristics. They possess a uniquely simple body plan, variably across five genera, two of which are rootless. Due to the existence of closely related species with a wide diversity in rooting strategies, duckweed roots represent a powerful system for investigating vestigiality. To explore this, we employed a panel of physiological, ionomic, and transcriptomic analyses, with the main goal of elucidating the extent of vestigiality in duckweed roots. We uncovered a progressive reduction in root anatomy as genera diverge and revealed that the root has lost its salient ancestral function as an organ required for supplying nutrients to the plant. Accompanying this, nutrient transporter expression patterns have lost the stereotypical root biased localization observed in other plant species. While other examples of organ loss such as limbs in reptiles4 or eyes in cavefish5 frequently display a binary of presence/absence, duckweeds provide a unique snapshot of an organ with varying degrees of vestigialization in closely related neighbors and thus provide a unique resource for exploration of how organs behave at different stages along the process of loss.

Endoreplication controls cell size via mechanochemical signaling.

During hypocotyl development, an asymmetric auxin gradient causes differential cell elongation, leading to tissue bending and apical hook formation. Recently, Ma et al. identified a molecular pathway that links auxin with endoreplication and cell size through cell wall integrity sensing, cell wall remodeling, and regulation of cell wall stiffness.

Transcription factor bHLH121 regulates root cortical aerenchyma formation in maize.

Root anatomical phenotypes present a promising yet underexploited avenue to deliver major improvements in yield and climate resilience of crops by improving water and nutrient uptake. For instance, the formation of root cortical aerenchyma (RCA) significantly increases soil exploration and resource capture by reducing the metabolic costs of root tissue. A key bottleneck in studying such phenotypes has been the lack of robust high-throughput anatomical phenotyping platforms. We exploited a phenotyping approach based on laser ablation tomography, termed Anatomics, to quantify variation in RCA formation of 436 diverse maize lines in the field. Results revealed a significant and heritable variation for RCA formation. Genome-wide association studies identified a single-nucleotide polymorphism mapping to a root cortex-expressed gene-encoding transcription factor bHLH121. Functional studies identified that the bHLH121 Mu transposon mutant line and CRISPR/Cas9 loss-of-function mutant line showed reduced RCA formation, whereas an overexpression line exhibited significantly greater RCA formation when compared to the wild-type line. Characterization of these lines under suboptimal water and nitrogen availability in multiple soil environments revealed that bHLH121 is required for RCA formation developmentally as well as under studied abiotic stress. Overall functional validation of the bHLH121 gene's importance in RCA formation provides a functional marker to select varieties with improved soil exploration and thus yield under suboptimal conditions.

Reviving grain quality in wheat through non-destructive phenotyping techniques like hyperspectral imaging.

A long-term goal of breeders and researchers is to develop crop varieties that can resist environmental stressors and produce high yields. However, prioritising yield often compromises improvement of other key traits, including grain quality, which is tedious and time-consuming to measure because of the frequent involvement of destructive phenotyping methods. Recently, non-destructive methods such as hyperspectral imaging (HSI) have gained attention in the food industry for studying wheat grain quality. HSI can quantify variations in individual grains, helping to differentiate high-quality grains from those of low quality. In this review, we discuss the reduction of wheat genetic diversity underlying grain quality traits due to modern breeding, key traits for grain quality, traditional methods for studying grain quality and the application of HSI to study grain quality traits in wheat and its scope in breeding. Our critical review of literature on wheat domestication, grain quality traits and innovative technology introduces approaches that could help improve grain quality in wheat.

Phosphite treatment can improve root biomass and nutrition use efficiency in wheat.

Phosphite represents a reduced form of phosphate that belongs to a class of crop growth-promoting chemicals termed biostimulants. Previous research has shown that phosphite application can enhance root growth, but its underlying mechanism, especially during environmental stresses, remains elusive. To uncover this, we undertook a series of morphological and physiological analyses under nutrient, water and heat stresses following a foliar application in wheat. Non-invasive 3D imaging of root system architecture directly in soil using X-ray Computed Tomography revealed that phosphite treatment improves root architectural traits and increased root biomass. Biochemical and physiological assays identified that phosphite treatment significantly increases Nitrate Reductase (NR) activity, leaf photosynthesis and stomatal conductance, suggesting improved Nitrogen and Carbon assimilation, respectively. These differences were more pronounced under heat or drought treatment (photosynthesis and photosystem II stability) and nutrient deficiency (root traits and NR). Overall our results suggest that phosphite treatment improves the ability of plants to tolerate abiotic stresses through improved Nitrogen and Carbon assimilation, combined with improved root growth which may improve biomass and yield.

Root angle is controlled by EGT1 in cereal crops employing an antigravitropic mechanism.

Root angle in crops represents a key trait for efficient capture of soil resources. Root angle is determined by competing gravitropic versus antigravitropic offset (AGO) mechanisms. Here we report a root angle regulatory gene termed ENHANCED GRAVITROPISM1 (EGT1) that encodes a putative AGO component, whose loss-of-function enhances root gravitropism. Mutations in barley and wheat EGT1 genes confer a striking root phenotype, where every root class adopts a steeper growth angle. EGT1 encodes an F-box and Tubby domain-containing protein that is highly conserved across plant species. Haplotype analysis found that natural allelic variation at the barley EGT1 locus impacts root angle. Gravitropic assays indicated that Hvegt1 roots bend more rapidly than wild-type. Transcript profiling revealed Hvegt1 roots deregulate reactive oxygen species (ROS) homeostasis and cell wall-loosening enzymes and cofactors. ROS imaging shows that Hvegt1 root basal meristem and elongation zone tissues have reduced levels. Atomic force microscopy measurements detected elongating Hvegt1 root cortical cell walls are significantly less stiff than wild-type. In situ analysis identified HvEGT1 is expressed in elongating cortical and stele tissues, which are distinct from known root gravitropic perception and response tissues in the columella and epidermis, respectively. We propose that EGT1 controls root angle by regulating cell wall stiffness in elongating root cortical tissue, counteracting the gravitropic machinery's known ability to bend the root via its outermost tissues. We conclude that root angle is controlled by EGT1 in cereal crops employing an antigravitropic mechanism.

Ethylene inhibits rice root elongation in compacted soil via ABA- and auxin-mediated mechanisms.

Soil compaction represents a major agronomic challenge, inhibiting root elongation and impacting crop yields. Roots use ethylene to sense soil compaction as the restricted air space causes this gaseous signal to accumulate around root tips. Ethylene inhibits root elongation and promotes radial expansion in compacted soil, but its mechanistic basis remains unclear. Here, we report that ethylene promotes abscisic acid (ABA) biosynthesis and cortical cell radial expansion. Rice mutants of ABA biosynthetic genes had attenuated cortical cell radial expansion in compacted soil, leading to better penetration. Soil compaction-induced ethylene also up-regulates the auxin biosynthesis gene OsYUC8. Mutants lacking OsYUC8 are better able to penetrate compacted soil. The auxin influx transporter OsAUX1 is also required to mobilize auxin from the root tip to the elongation zone during a root compaction response. Moreover, osaux1 mutants penetrate compacted soil better than the wild-type roots and do not exhibit cortical cell radial expansion. We conclude that ethylene uses auxin and ABA as downstream signals to modify rice root cell elongation and radial expansion, causing root tips to swell and reducing their ability to penetrate compacted soil.

Thermodynamic evaluation of solar assisted ZnO/Zn thermochemical CO2 splitting cycle.

The solar thermochemical CO2 splitting (CDS) is scrutinized via a redox ZnO/Zn cycle. The second law efficiency analysis is carried out by acquiring the required thermodynamic data from HSC Chemistry software. The main focus of this study is to explore the influence of reduction temperature (Tred), molar flow rate of inert sweep gas (n˙inert), and energy required for the gas separation on the solar-to-fuel energy conversion efficiency (ηsolar-to-fuel) of the ZnO/Zn cycle. All the calculations are conducted at a constant gas-to-gas heat recovery effectiveness (εgg) equal to 0.5. n˙inert required is recorded to be too high (5050 mol/s) at Tred equal to 1500 K and moderately low (15 mol/s) for Tred equal to 2000 K. The amount of thermal energy required to heat the inert/O2 gas mixture (from CDS temperature to separator-1 temperature) and inert sweep gas (from separator-1 temperature to reduction temperature) has a significant impact on the total thermal energy requirement of the cycle (Q˙TC). The rise in Tred from 1500 K to 2000 K shows a considerable decline in Q˙TC from 77417.5 kW to 1161.8 kW, respectively. Consequently, the highest ηsolar-to-fuel (17.0%) is recorded for Tred equal to 2000 K.

Root traits for low input agroecosystems in Africa: Lessons from three case studies.

In many regions across Africa, agriculture is largely based on low-input and small-holder farming systems that use little inorganic fertilisers and have limited access to irrigation and mechanisation. Improving agricultural practices and developing new cultivars adapted to these environments, where production already suffers from climate change, is a major priority for food security. Here, we illustrate how breeding for specific root traits could improve crop resilience in Africa using three case studies covering very contrasting low-input agroecosystems. We first review how greater basal root whorl number and longer and denser root hairs increased P acquisition efficiency and yield in common bean in South East Africa. We then discuss how water-saving strategies, root hair density and deep root growth could be targeted to improve sorghum and pearl millet yield in West Africa. Finally, we evaluate how breeding for denser root systems in the topsoil and interactions with arbuscular mycorrhizal fungi could be mobilised to optimise water-saving alternate wetting and drying practices in West African rice agroecosystems. We conclude with a discussion on how to evaluate the utility of root traits and how to make root trait selection feasible for breeders so that improved varieties can be made available to farmers through participatory approaches.

Significance of root hairs in developing stress-resilient plants for sustainable crop production.

Root hairs represent a beneficial agronomic trait to potentially reduce fertilizer and irrigation inputs. Over the past decades, research in the plant model Arabidopsis thaliana has provided insights into root hair development, the underlying genetic framework and the integration of environmental cues within this framework. Recent years have seen a paradigm shift, where studies are now highlighting conservation and diversification of root hair developmental programs in other plant species and the agronomic relevance of root hairs in a wider ecological context. In this review, we specifically discuss the molecular evolution of the RSL (RHD Six-Like) pathway that controls root hair development and growth in land plants. We also discuss how root hairs contribute to plant performance as an active physiological rooting structure by performing resource acquisition, providing anchorage and constructing the rhizosphere with desirable physical, chemical and biological properties. Finally, we outline future research directions that can help achieve the potential of root hairs in developing sustainable agroecosystems.

Root angle in maize influences nitrogen capture and is regulated by calcineurin B-like protein (CBL)-interacting serine/threonine-protein kinase 15 (ZmCIPK15).

Crops with reduced nutrient and water requirements are urgently needed in global agriculture. Root growth angle plays an important role in nutrient and water acquisition. A maize diversity panel of 481 genotypes was screened for variation in root angle employing a high-throughput field phenotyping platform. Genome-wide association mapping identified several single nucleotide polymorphisms (SNPs) associated with root angle, including one located in the root expressed CBL-interacting serine/threonine-protein kinase 15 (ZmCIPK15) gene (LOC100285495). Reverse genetic studies validated the functional importance of ZmCIPK15, causing a approximately 10° change in root angle in specific nodal positions. A steeper root growth angle improved nitrogen capture in silico and in the field. OpenSimRoot simulations predicted at 40 days of growth that this change in angle would improve nitrogen uptake by 11% and plant biomass by 4% in low nitrogen conditions. In field studies under suboptimal N availability, the cipk15 mutant with steeper growth angles had 18% greater shoot biomass and 29% greater shoot nitrogen accumulation compared to the wild type after 70 days of growth. We propose that a steeper root growth angle modulated by ZmCIPK15 will facilitate efforts to develop new crop varieties with optimal root architecture for improved performance under edaphic stress.

Plant roots sense soil compaction through restricted ethylene diffusion.

Soil compaction represents a major challenge for modern agriculture. Compaction is intuitively thought to reduce root growth by limiting the ability of roots to penetrate harder soils. We report that root growth in compacted soil is instead actively suppressed by the volatile hormone ethylene. We found that mutant Arabidopsis and rice roots that were insensitive to ethylene penetrated compacted soil more effectively than did wild-type roots. Our results indicate that soil compaction lowers gas diffusion through a reduction in air-filled pores, thereby causing ethylene to accumulate in root tissues and trigger hormone responses that restrict growth. We propose that ethylene acts as an early warning signal for roots to avoid compacted soils, which would be relevant to research into the breeding of crops resilient to soil compaction.