Epigenetic modifications regulate cultivar-specific root development and metabolic adaptation to nitrogen availability in wheat.

The breeding of crops with improved nitrogen use efficiency (NUE) is crucial for sustainable agriculture, but the involvement of epigenetic modifications remains unexplored. Here, we analyze the chromatin landscapes of two wheat cultivars (KN9204 and J411) that differ in NUE under varied nitrogen conditions. The expression of nitrogen metabolism genes is closely linked to variation in histone modification instead of differences in DNA sequence. Epigenetic modifications exhibit clear cultivar-specificity, which likely contributes to distinct agronomic traits. Additionally, low nitrogen (LN) induces H3K27ac and H3K27me3 to significantly enhance root growth in KN9204, while remarkably inducing NRT2 in J411. Evidence from histone deacetylase inhibitor treatment and transgenic plants with loss function of H3K27me3 methyltransferase shows that changes in epigenetic modifications could alter the strategy preference for root development or nitrogen uptake in response to LN. Here, we show the importance of epigenetic regulation in mediating cultivar-specific adaptation to LN in wheat.

Dissection and validation of a promising QTL controlling spikelet number on 5B in bread wheat.

KEY MESSAGE: Five environmentally stable QTLs for spikelet number per spike and days to heading were identified using a high-genetic map containing 95,444 SNPs, among which QSns.ucas-5B was validated using residual heterozygous line at multiple environments. Spikelet number per spike (SNS) and days to heading (DTH) play pivotal roles in the improvement of wheat yield. In this study, a high-density genetic map for a recombinant inbred lines (RILs) population derived from Zhengnong 17 (ZN17) and Yangbaimai (YBM) was constructed using 95,444 single-nucleotide polymorphism (SNP) markers from the Wheat660K SNP array. Our study identified a total of five environmentally stable QTLs for SNS and DTH, one of which was named QSns.ucas-5B, with a physical interval of approximately 545.4-552.1 Mb on the 5BL chromosome arm. Importantly, the elite haplotype within QSns.ucas-5B showed a consistent and positive effect on SNS, grain number and weight per spike, without extending the days to heading. These findings provide a foundation for future efforts to map and clone the gene(s) responsible for QSns.ucas-5B and further indicate the potential application of the developed and validated InDel marker of QSns.ucas-5B for molecular breeding purposes, aimed at improving wheat grain yield.

Iron in the Symbiosis of Plants and Microorganisms.

Iron is an essential element for most organisms. Both plants and microorganisms have developed different mechanisms for iron uptake, transport and storage. In the symbiosis systems, such as rhizobia-legume symbiosis and arbuscular mycorrhizal (AM) symbiosis, maintaining iron homeostasis to meet the requirements for the interaction between the host plants and the symbiotic microbes is a new challenge. This intriguing topic has drawn the attention of many botanists and microbiologists, and many discoveries have been achieved so far. In this review, we discuss the current progress on iron uptake and transport in the nodules and iron homeostasis in rhizobia-legume symbiosis. The discoveries with regard to iron uptake in AM fungi, iron uptake regulation in AM plants and interactions between iron and other nutrient elements during AM symbiosis are also summarized. At the end of this review, we propose prospects for future studies in this fascinating research area.

Whole-genome sequencing of diverse wheat accessions uncovers genetic changes during modern breeding in China and the United States.

Breeding has dramatically changed the plant architecture of wheat (Triticum aestivum), resulting in the development of high-yielding varieties adapted to modern farming systems. However, how wheat breeding shaped the genomic architecture of this crop remains poorly understood. Here, we performed a comprehensive comparative analysis of a whole-genome resequencing panel of 355 common wheat accessions (representing diverse landraces and modern cultivars from China and the United States) at the phenotypic and genomic levels. The genetic diversity of modern wheat cultivars was clearly reduced compared to landraces. Consistent with these genetic changes, most phenotypes of cultivars from China and the United States were significantly altered. Of the 21 agronomic traits investigated, 8 showed convergent changes between the 2 countries. Moreover, of the 207 loci associated with these 21 traits, more than half overlapped with genomic regions that showed evidence of selection. The distribution of selected loci between the Chinese and American cultivars suggests that breeding for increased productivity in these 2 regions was accomplished by pyramiding both shared and region-specific variants. This work provides a framework to understand the genetic architecture of the adaptation of wheat to diverse agricultural production environments, as well as guidelines for optimizing breeding strategies to design better wheat varieties.

The SOD7/DPA4-GIF1 module coordinates organ growth and iron uptake in Arabidopsis.

Organ growth is controlled by both intrinsic genetic factors and external environmental signals. However, the molecular mechanisms that coordinate plant organ growth and nutrient supply remain largely unknown. We have previously reported that the B3 domain transcriptional repressor SOD7 (NGAL2) and its closest homologue DPA4 (NGAL3) act redundantly to limit organ and seed growth in Arabidopsis. Here we report that SOD7 represses the interaction between the transcriptional coactivator GRF-INTERACTING FACTOR 1 (GIF1) and growth-regulating factors (GRFs) by competitively interacting with GIF1, thereby limiting organ and seed growth. We further reveal that GIF1 physically interacts with FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT), which acts as a central regulator of iron uptake and homeostasis. SOD7 can competitively repress the interaction of GIF1 with FIT to influence iron uptake and responses. The sod7-2 dpa4-3 mutant enhances the expression of genes involved in iron uptake and displays high iron accumulation. Genetic analyses support that GIF1 functions downstream of SOD7 to regulate organ and seed growth as well as iron uptake and responses. Thus, our findings define a previously unrecognized mechanism that the SOD7/DPA4-GIF1 module coordinates organ growth and iron uptake by targeting key regulators of growth and iron uptake.

A Wheat 660 K SNP array-based high-density genetic map facilitates QTL mapping of flag leaf-related traits in wheat.

KEY MESSAGE: A high-density genetic map containing 122,620 SNP markers was constructed, which facilitated the identification of eight major flag leaf-related QTL in relatively narrow intervals. The flag leaf plays an important role in photosynthetic capacity and yield potential in wheat. In this study, we used a recombinant inbred line population containing 188 lines derived from a cross between 'Lankao86' (LK86) and 'Ermangmai' to construct a genetic map using the Wheat 660 K single-nucleotide polymorphism (SNP) array. The high-density genetic map contains 122,620 SNP markers spanning 5185.06 cM. It shows good collinearity with the physical map of Chinese Spring and anchors multiple sequences of previously unplaced scaffolds onto chromosomes. Based on the high-density genetic map, we identified seven, twelve, and eight quantitative trait loci (QTL) for flag leaf length (FLL), width (FLW), and area (FLA) across eight environments, respectively. Among them, three, one, and four QTL for FLL, FLW, and FLA are major and stably express in more than four environments. The physical distance between the flanking markers for QFll.igdb-3B/QFlw.igdb-3B/QFla.igdb-3B is only 444 kb containing eight high confidence genes. These results suggested that we could directly map the candidate genes in a relatively small region by the high-density genetic map constructed with the Wheat 660 K array. Furthermore, the identification of environmentally stable QTL for flag leaf morphology laid a foundation for the following gene cloning and flag leaf morphology improvement.

Wheat genomic study for genetic improvement of traits in China.

Bread wheat (Triticum aestivum L.) is a major crop that feeds 40% of the world's population. Over the past several decades, advances in genomics have led to tremendous achievements in understanding the origin and domestication of wheat, and the genetic basis of agronomically important traits, which promote the breeding of elite varieties. In this review, we focus on progress that has been made in genomic research and genetic improvement of traits such as grain yield, end-use traits, flowering regulation, nutrient use efficiency, and biotic and abiotic stress responses, and various breeding strategies that contributed mainly by Chinese scientists. Functional genomic research in wheat is entering a new era with the availability of multiple reference wheat genome assemblies and the development of cutting-edge technologies such as precise genome editing tools, high-throughput phenotyping platforms, sequencing-based cloning strategies, high-efficiency genetic transformation systems, and speed-breeding facilities. These insights will further extend our understanding of the molecular mechanisms and regulatory networks underlying agronomic traits and facilitate the breeding process, ultimately contributing to more sustainable agriculture in China and throughout the world.

Comparative genomic and transcriptomic analyses uncover the molecular basis of high nitrogen-use efficiency in the wheat cultivar Kenong 9204.

Studying the regulatory mechanisms that drive nitrogen-use efficiency (NUE) in crops is important for sustainable agriculture and environmental protection. In this study, we generated a high-quality genome assembly for the high-NUE wheat cultivar Kenong 9204 and systematically analyzed genes related to nitrogen uptake and metabolism. By comparative analyses, we found that the high-affinity nitrate transporter gene family had expanded in Triticeae. Further studies showed that subsequent functional differentiation endowed the expanded family members with saline inducibility, providing a genetic basis for improving the adaptability of wheat to nitrogen deficiency in various habitats. To explore the genetic and molecular mechanisms of high NUE, we compared genomic and transcriptomic data from the high-NUE cultivar Kenong 9204 (KN9204) and the low-NUE cultivar Jing 411 and quantified their nitrogen accumulation under high- and low-nitrogen conditions. Compared with Jing 411, KN9204 absorbed significantly more nitrogen at the reproductive stage after shooting and accumulated it in the shoots and seeds. Transcriptome data analysis revealed that nitrogen deficiency clearly suppressed the expression of genes related to cell division in the young spike of Jing 411, whereas this suppression of gene expression was much lower in KN9204. In addition, KN9204 maintained relatively high expression of NPF genes for a longer time than Jing 411 during seed maturity. Physiological and transcriptome data revealed that KN9204 was more tolerant of nitrogen deficiency than Jing 411, especially at the reproductive stage. The high NUE of KN9204 is an integrated effect controlled at different levels. Taken together, our data provide new insights into the molecular mechanisms of NUE and important gene resources for improving wheat cultivars with a higher NUE trait.

Requirement and functional redundancy of two large ribonucleotide reductase subunit genes for cell cycle, chloroplast biogenesis and photosynthesis in tomato.

BACKGROUND AND AIMS: Ribonucleotide reductase (RNR), functioning in the de novo synthesis of deoxyribonucleoside triphosphates (dNTPs), is crucial for DNA replication and cell cycle progression. In most plants, the large subunits of RNR have more than one homologous gene. However, the different functions of these homologous genes in plant development remain unknown. In this study, we obtained the mutants of two large subunits of RNR in tomato and studied their functions. METHODS: The mutant ylc1 was obtained by ethyl methyl sulfonate (EMS) treatment. Through map-based cloning, complementation and knock-out experiments, it was confirmed that YLC1 encodes a large subunit of RNR (SlRNRL1). The expression level of the genes related to cell cycle progression, chloroplast biogenesis and photosynthesis was assessed by RNA-sequencing. In addition, we knocked out SlRNRL2 (a SlRNRL1 homologue) using CRISPR-Cas9 technology in the tomato genome, and we down-regulated SlRNRL2 expression in the genetic background of slrnrl1-1 using a tobacco rattle virus-induced gene silencing (VIGS) system. KEY RESULTS: The mutant slrnrl1 exhibited dwarf stature, chlorotic young leaves and smaller fruits. Physiological and transcriptomic analyses indicated that SlRNRL1 plays a crucial role in the regulation of cell cycle progression, chloroplast biogenesis and photosynthesis in tomato. The slrnrl2 mutant did not exhibit any visible phenotype. SlRNRL2 has a redundant function with SlRNRL1, and the double mutant slrnrl1slrnrl2 is lethal. CONCLUSIONS: SlRNRL1 is essential for cell cycle progression, chloroplast biogenesis and photosynthesis. In addition, SlRNRL1 and SlRNRL2 possess redundant functions and at least one of these RNRLs is required for tomato survival, growth and development.

Fine mapping of the tiller inhibition gene TIN5 in Triticum urartu.

KEY MESSAGE: A tiller inhibition gene TIN5 was delimited to an approximate 2.1 Mb region on chromosome Tu7 that contains 24 annotated genes. Grain yield in wheat (Triticum aestivum L.) is a polygenic trait representing many developmental processes and their interactions with the environments. Among them, tillering capacity is an important agronomic trait for plant architecture and grain yield, but the genetic basis of tiller formation in wheat remains largely unknown. In this study, we identified a tiller inhibition 5 (tin5) mutant from ethyl methane sulfonate treated G1812 (Triticum urartu Thumanjan ex Gandilyan). A mapping population was constructed with tin5/G3146. Based on the sequence differences between G1812 and G3146, large insertions and deletions (≥ 5 bp) were selected and verified, and a skeleton physical map was constructed with genome-wide 168 polymorphic InDel markers. Genetic analysis revealed that the low-tiller phenotype was controlled by a single recessive locus, which we named TIN5. This locus was mapped to a 2.1-Mb region that contained 24 annotated genes on chromosome Tu7. Among these annotated genes, only TuG1812G0700004539 showed a non-synonymous polymorphism between tin5 and the wild type. Our finding will facilitate its map-based cloning and pave the way for an in-depth analysis of the underlying genetic basis of tiller formation and regulation patterns.

Crosstalk Between Iron and Sulfur Homeostasis Networks in Arabidopsis.

The widespread deficiency of iron (Fe) and sulfur (S) is becoming a global concern. The underlying mechanisms regulating Fe and S sensing and signaling have not been well understood. We investigated the crosstalk between Fe and S using mutants impaired in Fe homeostasis, sulfate assimilation, and glutathione (GSH) biosynthesis. We showed that chlorosis symptoms induced by Fe deficiency were not directly related to the endogenous GSH levels. We found dynamic crosstalk between Fe and S networks and more interestingly observed that the upregulated expression of IRT1 and FRO2 under S deficiency in Col-0 was missing in the cad2-1 mutant background, which suggests that under S deficiency, the expression of IRT1 and FRO2 was directly or indirectly dependent on GSH. Interestingly, the bottleneck in sulfite reduction led to a constitutively higher IRT1 expression in the sir1-1 mutant. While the high-affinity sulfate transporter (Sultr1;2) was upregulated under Fe deficiency in the roots, the low-affinity sulfate transporters (Sultr2;1, and Sultr2;2) were down-regulated in the shoots of Col-0 seedlings. Moreover, the expression analysis of some of the key players in the Fe-S cluster assembly revealed that the expression of the so-called Fe donor in mitochondria (AtFH) and S mobilizer of group II cysteine desulfurase in plastids (AtNFS2) were upregulated under Fe deficiency in Col-0. Our qPCR data and ChIP-qPCR experiments suggested that the expression of AtFH is likely under the transcriptional regulation of the central transcription factor FIT.

Biofortification of iron and zinc in rice and wheat.

Iron and zinc are critical micronutrients for human health. Approximately two billion people suffer from iron and zinc deficiencies worldwide, most of whom rely on rice (Oryza sativa) and wheat (Triticum aestivum) as staple foods. Therefore, biofortifying rice and wheat with iron and zinc is an important and economical approach to ameliorate these nutritional deficiencies. In this review, we provide a brief introduction to iron and zinc uptake, translocation, storage, and signaling pathways in rice and wheat. We then discuss current progress in efforts to biofortify rice and wheat with iron and zinc. Finally, we provide future perspectives for the biofortification of rice and wheat with iron and zinc.

AtCPS V326M significantly affect the biosynthesis of gibberellins.

Gibberellins are a class of typical phytohormones, which regulate plant growth and development. The contents of gibberellins dramatically affect the morphology and biomass of plant. The encoding protein of copalyl diphosphate synthase gene (CPS) catalyzes the first-step in the biosynthetic pathway of gibberellins. The mutation in this gene may significantly affect the contents of gibberellins in plants. In this study, we found an EMS-triggered mutant, ga1-168, showing short roots, short hypocotyls, late flowering and dwarf. Map-based cloning revealed that the causal gene of ga1-168 was AtCPS-168, an allele of AtCPS gene. The encoding protein of AtCPS-168 was AtCPS V326M which was resulted from a single-point mutation (guanine to adenine at nucleotide 2768) of AtCPS gene. Protein domain analysis showed that V326 was located in the Terpene_synth domain. The allelism test demonstrated that AtCPS-168 was an allele of AtCPS gene. The transgenic complementation of ga1-168 indicated that AtCPS V326M led to the dwarf and bushy phenotype of ga1-168. The endogenous gibberellins contents analysis suggested that the gibberellins contents of ga1-168 were much lower than that of wild-type. The exogenous GA3 application assay uncovered that application of GA3 can complement the dwarf and bushy phenotype of ga1-168 caused by low endogenous gibberellins contents. Therefore, this study suggested that it is an elegant way to create the ideal plant architecture and height by site-directed mutating the gibberellin biosynthetic genes.

Ne2, a typical CC-NBS-LRR-type gene, is responsible for hybrid necrosis in wheat.

Hybrid necrosis, caused by complementary genes Ne1 and Ne2, is a serious barrier for combining desirable traits from different genotypes of wheat, affecting the full utilisation of heterosis. To date, both Ne1 and Ne2 are still not isolated although they were documented decades ago. We report here the map-based cloning and functional characterisation of Ne2, encoding a coiled coil-nucleotide-binding site-leucine-rich repeat (CC-NBS-LRR) protein. Homozygous frameshift mutations generated using the CRISPR/Cas9 approach confirmed the Ne2-inducing hybrid necrosis in wheat. Upregulated expression of Ne2 induced by Ne1 and excess hydrogen peroxide accumulation are associated with the necrosis formation. Genetic analyses of a Ne2 allele (Ne2m ) and leaf rust resistance gene LrLC10/Lr13 revealed that they might be the same gene. Furthermore, we demonstrated that the frequency of the Ne2 allele was much lower in landraces (2.00%) compared with that in modern cultivars (13.62%), suggesting that Ne2 allele has been partially applied in wheat genetic improvement. Our findings open opportunities of thoroughly investigating the molecular mechanism of hybrid necrosis, selecting Lr13 and simultaneously avoiding hybrid necrosis in wheat breeding through marker-assisted selection.

Fine mapping of hybrid necrosis gene Ne1 in common wheat (Triticum aestivum L.).

KEY MESSAGE: Hybrid necrosis gene Ne1 was delimited into an approximate 4.06 Mb region on chromosome arm 5BL and an InDel marker that co-segregated with Ne1 alleles was developed. Hybrid necrosis in wheat, characterized by progressive chlorosis and necrosis of plant leaves, tillers or whole plants in certain hybrids, is caused by complementary genes Ne1 and Ne2 located on chromosome arms 5BL and 2BS, respectively. Hybrid necrosis can be a barrier in combining desirable traits from various wheat genotypes. In this study, we fine mapped Ne1 on chromosome arm 5BL, and delimited it to a 4.06 Mb region using large segregating recombinant inbred line families from cross 'Zhengnong 17' × 'Yangbaimai'. Genetic characterization confirmed that the ne1 allele was closely associated with a 2.89 Mb deletion in Zhengnong 17. A tightly linked InDel marker, 5B-InDel385, for Ne1 was developed and was used to predict the presence of Ne1 in a diverse panel of 501 common wheat accessions. Among those accessions, 122 (61%) of 200 landraces were predicted to carry the Ne1 allele, whereas only 79 (26%) of 301 modern cultivars were predicted to carry Ne1. The significant decrease in Ne1 frequency in modern cultivars indicated that the Ne1 allele had been negatively selected in wheat breeding. This study provides a foundation for marker-assisted selection, gene cloning and functional studies of Ne1 in wheat.

Iron in plant-pathogen interactions.

Iron is an essential element for most organisms. As an indispensable co-factor of many enzymes, iron is involved in various crucial metabolic processes that are required for the survival of plants and pathogens. Conversely, excessive iron produces highly active reactive oxygen species, which are toxic to the cells of plants and pathogens. Therefore, plants and pathogens have evolved sophisticated mechanisms to modulate iron status at a moderate level for maintaining their fitness. Over the past decades, many efforts have been made to reveal these mechanisms, and some progress has been made. In this review, we describe recent advances in understanding the roles of iron in plant-pathogen interactions and propose prospects for future studies.

Glutamate synthase 1 is involved in iron-deficiency response and long-distance transportation in Arabidopsis.

Iron is an essential microelement for plant growth. After uptake from the soil, iron is chelated by ligands and translocated from roots to shoots for subsequent utilization. However, the number of ligands involved in iron chelation is unclear. In this study, we identified and demonstrated that GLU1, which encodes a ferredoxin-dependent glutamate synthase, was involved in iron homeostasis. First, the expression of GLU1 was strongly induced by iron deficiency condition. Second, lesion of GLU1 results in reduced transcription of many iron-deficiency-responsive genes in roots and shoots. The mutant plants revealed a decreased iron concentration in the shoots, and displayed severe leaf chlorosis under the condition of Fe limitation, compared to wild-type. Third, the product of GLU1, glutamate, could chelate iron in vivo and promote iron transportation. Last, we also found that supplementation of glutamate in the medium can alleviate cadmium toxicity in plants. Overall, our results provide evidence that GLU1 is involved in iron homeostasis through affecting glutamate synthesis under iron deficiency conditions in Arabidopsis.

Cysteine protease RD21A regulated by E3 ligase SINAT4 is required for drought-induced resistance to Pseudomonas syringae in Arabidopsis.

Plants can be simultaneously exposed to multiple stresses. The interplay of abiotic and biotic stresses may result in synergistic or antagonistic effects on plant development and health. Temporary drought stress can stimulate plant immunity; however, the molecular mechanism of drought-induced immunity is largely unknown. In this study, we demonstrate that cysteine protease RD21A is required for drought-induced immunity. Temporarily drought-treated wild-type Arabidopsis plants became more sensitive to the bacterial pathogen-associated molecular pattern flg22, triggering stomatal closure, which resulted in increased resistance to Pseudomonas syringae pv. tomato DC3000 (Pst-DC3000). Knocking out rd21a inhibited flg22-triggered stomatal closure and compromised the drought-induced immunity. Ubiquitin E3 ligase SINAT4 interacted with RD21A and promoted its degradation in vivo. The overexpression of SINAT4 also consistently compromised the drought-induced immunity to Pst-DC3000. A bacterial type III effector, AvrRxo1, interacted with both SINAT4 and RD21A, enhancing SINAT4 activity and promoting the degradation of RD21A in vivo. Therefore, RD21A could be a positive regulator of drought-induced immunity, which could be targeted by pathogen virulence effectors during pathogenesis.

[Development and application of the plant phenomics analysis platform].

With the completion of the whole genome sequencing of major important crops, researchers have an increasing demand for high-throughput, accurate and nondestructive phenotyping technologies. The Plant Phenomics Analysis Platform (PPAP) was established in 2017 at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences. The platform has the most up-to-date comprehensive phenotyping analysis facility in China with a full spectrum of imaging systems consisting of eight units including visible light, infrared, near-infrared, root near-infrared, fluorescence, chlorophyll fluorescence, high spectral and lidar imaging. The platform has also specifically established phenotyping technologies for complex traits, such as root phenotype collection and analysis, spike and spikelet feature collection and analysis and responses under stress conditions. PPAP is dedicated to providing all-possible services for domestic and international academic communities and industrial partners engaged in plant sciences.

[Progress on wheat A genome illustration and its evolutional analysis].

Wheat is one of the main food crops and widely grown in the world. It feeds more than 35% of the world's population. Obtaining high-quality genome sequences of wheat is important for its basic and breeding researches. However, the large and complex genome of wheat once led to its genome sequencing as an "impossible task". Recently, with the development of high-throughput sequencing and assembly technology, many wheat genome sequences have been released, and their sequencing and assembly quality is being improved continuously. In the last two years, five wheat reference genomes with different ploidy levels have been published, including two diploid ancestors Triticum urartu (AA) and Aegilops tauschii (DD), wild and cultivated tetraploid wheat T. turgidum ssp. dicoccoides (BBAA) and hexaploid wheat T. aestivum (BBAADD). Among them, the sequencing and analysis of the T. urartu genome, a donor of polyploid wheat A subgenome, was led by the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences. In this review, we summarize the research progress on structure and evolution analyses of the T. urartu genome to provide some valuable information for promoting the basic and applied researches of wheat.