OsNBL3, a mitochondrion-localized pentatricopeptide repeat protein, is involved in splicing nad5 intron 4 and its disruption causes lesion mimic phenotype with enhanced resistance to biotic and abiotic stresses

Lesion Mimic Mutant: An Ideal Genetic Material for Deciphering the Balance Between Plant Immunity and Growth

Lesion mimic mutants (LMMs) form hypersensitive response (HR)-like lesions, a form of programmed cell death (PCD), in the absence of pathogens, that often confer durable and broad-spectrum disease resistance, representing a potential source for breeding resistance. However, most LMM plants have significant growth retardation including cell death, leaf senescence, damaged chloroplast structure, decreased chlorophyll contents, and undesirable agronomic traits. Therefore, LMMs represent ideal genetic materials to decipher interactions between defense signaling and programmed cell death, and growth. Many LMMs have been identified in rice, and at least 61 genes have been cloned and functionally confirmed. LMM genes are reported to participate in various regulation pathways, including gene transcription and protein translation, ubiquitin-proteasome pathway, protein phosphorylation, vesicle trafficking, metabolic pathways, and phytohormone signaling, highlighting the complexity of regulatory mechanisms. This review discusses recent progress on characteristics of rice LMM and mechanisms of LMM gene regulation, and suggests directions for future theoretical research and the potential use of LMMs in rice breeding.

Organelle genomes of two Scaevola species, S. taccada and S. hainanensis, provide new insights into evolutionary divergence between Scaevola and its related species

Chloroplast and mitochondrial genomes harbor crucial information that can be utilized for elucidating plant evolution and environmental adaptation. The organellar genomic characteristics of Goodeniaceae, a sister family to Asteraceae, remain unexplored. Here, using a combination of short-read and long-read sequencing technologies, we successfully assembled the complete organellar genomes of two Goodeniaceae species native to China, Scaevola taccada and S. hainanensis. Chloroplast genome collinearity analysis revealed that Scaevola expanded its genome length through inverted repeat expansion and large single copy fragment duplication, resulting in 181,022 bp (S. taccada) and 182,726 bp (S. hainanensis), ~30 kb increase compared to its related species. Mitochondrial genomes of two Scaevola species exhibit multi-ring topology, forming dual mitochondrial chromosomes of 314,251 bp (S. taccada) and 276,175 bp (S. hainanensis). Sequence variation analysis demonstrated substantial chloroplast sequence divergence (Pi = 0.45) and an increase in gene copy number within the genus. Relative synonymous codon usage (RSCU) analysis revealed that Scaevola chloroplast has a higher bias for A/U-ending codons than mitochondria, with chloroplasts RSCU values ranging from 0.32 to 1.94, whereas mitochondrial RSCU values ranging from 0.38 to 1.62. Phylogenetic analyses support the monophyly of the Asteraceae-Goodeniaceae sister group, whereas the extended evolutionary branches of Scaevola, coupled with mitochondrial collinearity analysis, indicate rapid organellar genome evolution of Scaevola. Organellar-nuclear horizontal gene transfer analysis identified specific increased in the copy numbers of photosynthesis-related genes and chloroplast-nuclear transfer events in S. taccada. Our study not only provides insights for understanding environmental adaptation mechanisms of coastal plants, but also contributes to elucidating organellar genome evolution in Scaevola and Goodeniaceae.

Rice Cytochrome P450 Protein CYP71P1 Is Required for Heat Stress Tolerance by Regulating Serotonin Biosynthesis and ROS Homeostasis

Heat stress is one of the major factors affecting crop growth and yield. However, the molecular mechanisms underlying rice heat stress tolerance remain largely unclear. In this study, we identified and characterized the rice high temperature sensitive 2 (hts2) mutant, which is highly susceptible to heat stress. Map-based cloning revealed that the HTS2 encodes a cytochrome P450 protein (CYP71P1) involved in serotonin biosynthesis. HTS2 is ubiquitously expressed across plant tissues and shows strong upregulation in response to heat stress. The HTS2 mutation significantly impairs basal serotonin synthesis in rice, and the heat-sensitive phenotype of the hts2 mutant is completely rescued by exogenous serotonin supplementation. Compared to the wild type, the hts2 mutant exhibits reduced antioxidant capacity, leading to excessive reactive oxygen species (ROS) accumulation and severe oxidative damage, ultimately reducing heat stress tolerance. Furthermore, disruption of HTS2 significantly affects the rice heat shock response, with the heat-induced expression of HsfA2s and their downstream target genes, such as HSP18.0 (heat shock protein 18.0) and OsAPX2 (ascorbate peroxidase 2), markedly depressed in hts2 mutant. Our results suggest a pivotal role of HTS2 in modulating serotonin metabolism and maintaining ROS homeostasis during heat stress, offering new perspectives on the mechanisms underlying heat tolerance and potential strategies to enhance rice resilience to heat stress.

The Pentatricopeptide Repeat Protein OsPPR674 Regulates Rice Growth and Drought Sensitivity by Modulating RNA Editing of the Mitochondrial Transcript ccmC

The P-type pentatricopeptide repeat (PPR) proteins are crucial for RNA editing and post-transcriptional regulation in plant organelles, particularly mitochondria. This study investigates the role of OsPPR674 in rice, focusing on its function in mitochondrial RNA editing. Using CRISPR/Cas9 technology, we generated ppr674 mutant and examined its phenotypic and molecular characteristics. The results indicate that ppr674 exhibits reduced plant height, decreased seed-setting rate, and poor drought tolerance. Further analysis revealed that in the ppr674 mutant, RNA editing at the 299th nucleotide position of the mitochondrial ccmC gene (C-to-U conversion) was abolished. REMSAs showed that GST-PPR674 specifically binds to RNA probes targeting this ccmC-299 site, confirming its role in this editing process. In summary, these results suggest that OsPPR674 plays a pivotal role in mitochondrial RNA editing, emphasizing the significance of PPR proteins in organelle function and plant development.

Pentatricopeptide repeat proteins in plants: Cellular functions, action mechanisms, and potential applications

Pentatricopeptide repeat (PPR) proteins are involved in nearly all aspects of post-transcriptional processing in plant mitochondria and plastids, playing vital roles in plant growth, development, cytoplasmic male sterility restoration, and responses to biotic and abiotic stresses. Over the last three decades, significant advances have been made in understanding the functions of PPR proteins and the primary mechanisms through which they mediate post-transcriptional processing. This review aims to summarize these advancements, highlighting the mechanisms by which PPR proteins facilitate RNA editing, intron splicing, and RNA maturation in the context of organellar gene expression. We also present the latest progress in PPR engineering and discuss its potential as a biotechnological tool. Additionally, we discuss key challenges and questions that remain in PPR research.

RAS, a Pentatricopeptide Repeat Protein, Interacts with OsTRX z to Regulate Chloroplast Gene Transcription and RNA Processing

Thioredoxin z (TRX z) plays a significant role in chloroplast development by regulating the transcription of chloroplast genes. In this study, we identified a pentatricopeptide repeat (PPR) protein, rice albino seedling-lethal (RAS), that interacts with OsTRX z. This interaction was initially discovered by using a yeast two-hybrid (Y2H) screening technique and was further validated through Y2H and bimolecular fluorescence complementation (BiFC) experiments. RAS contains 16 PPR motifs and features a small MutS-related (SMR) domain at its C-terminus. CRISPR/Cas9-generated ras mutants exhibited an albino seedling-lethal phenotype characterized by abnormal chloroplast structures and a significantly reduced chlorophyll content. RAS localizes to the chloroplast and is predominantly expressed in young leaves. Mutations in RAS affect RNA editing at the rpl2, rps14, and ndhA sites, as well as RNA splicing at the rpl2, atpF, and ndhA transcripts within the chloroplast. Furthermore, the expression levels of genes associated with chloroplast formation are altered in the ras mutant. Both OsTRX z and RAS were found to interact with chloroplast signal recognition particle (cpSRP) proteins, indicating that their proper localization within the chloroplast may be dependent on the SRP pathway. Collectively, our findings highlight the critical role of RAS in chloroplast development, as it is involved in RNA processing and the regulation of chloroplast gene expression.

Mitochondrial Splicing Efficiency Is Lower in Holoparasites Than in Free-Living Plants

Mitochondria play a crucial role in eukaryotic organisms, housing their own genome with genes vital for oxidative phosphorylation. Coordination between nuclear and mitochondrial genomes is pivotal for organelle gene expression. Splicing, editing and processing of mitochondrial transcripts are regulated by nuclear-encoded factors. Splicing efficiency (SEf) of the many group II introns present in plant mitochondrial genes is critical for mitochondrial function since a splicing defect or splicing deficiency can severely impact plant growth and development. This study investigates SEf in free-living and holoparasitic plants, focusing on 25 group II introns from 15 angiosperm species. Our comparative analyses reveal distinctive splicing patterns with holoparasites exhibiting significantly lower SEf, potentially linked to their unique evolutionary trajectory. Given the preponderance of horizontal gene transfer (HGT) in parasitic plants, we investigated the effect of HGT on SEf, such as the presence of foreign introns or foreign nuclear-encoded splicing factors. Contrary to expectations, the SEf reductions do not correlate with HGT events, suggesting that other factors are at play, such as the loss of photosynthesis or the transition to a holoparasitic lifestyle. The findings of this study broaden our understanding of the molecular evolution in parasitic plants and shed light on the multifaceted factors influencing organelle gene expression.

Novel SNPs Linked to Blast Resistance Genes Identified in Pearl Millet Through Genome-Wide Association Models

Foliar blast, caused by Pyricularia grisea, poses a major challenge to pearl millet (Pennisetum glaucum (L.) R. Br) production, leading to severe yield losses, particularly in rainfed ecologies. This study aimed to elucidate the genetic basis of blast resistance through a genome-wide association study (GWAS) involving 281 diverse pearl millet inbreds. GWAS panel was phenotyped for blast resistance against three distinct isolates of P. grisea collected from Delhi, Gujarat, and Rajasthan locations, revealing a significant variability with 16.7% of the inbreds showing high resistance. Bayesian information and linkage disequilibrium iteratively nested keyway (BLINK) and Multi-Locus Mixed Model (MLMM) models using transformed means identified 68 significant SNPs linked to resistance, with hotspots for resistance-related genes on chromosomes 1, 2, and 6. These regions harbor genes involved in defense mechanisms, including immune response, stress tolerance, signal transduction, transcription regulation, and pathogen defense. Genes, namely 14-3-3-like proteins RGA2, RGA4, hypersensitive-induced response proteins, NHL3, NBS-LRR, LRR-RLK, LRRNT_2, and various transcription factors such as AP2/ERF and WRKY, played a crucial role in the stress-responsive pathways. Analyses of transporter proteins, redox processes, and structural proteins revealed additional mechanisms contributing to blast resistance. This study offers valuable insights into the complex genetic architecture of blast resistance in pearl millet, offering a solid foundation for marker-assisted breeding programs and gene-editing experiments.

Three New Species and Five New Host Records from Chaetomiaceae with Anti-Phytopathogenic Potential from Cover Crops Astragalus sinicus and Vicia villosa

Cover crops, typically planted during off-seasons and requiring less agronomic manipulation, may provide abundant fungal resources. Certain species of Chaetomiaceae could serve as potential agents for controlling plant diseases and developing bioorganic fertilizers. Eight species from five genera of Chaetomiaceae were identified from healthy Astragalus sinicus and Vicia villosa, two major cover crops, through multigene phylogenetic analysis, morphological identification, and pairwise homoplasy index testing. The identified species comprise three new species: Achaetomium astragali, Subramaniula henanensis, and S. sichuanensis, as well as five known but new host record species: Botryotrichum murorum, Chaetomium coarctatum, C. pseudocochliodes, C. pseudoglobosum, and Collariella pachypodioides. Dual culture tests revealed that isolates of all eight Chaetomiaceae species exhibited antagonistic effects on multiple phytopathogens. Among the identified fungi, the NSJA2 isolate, belonging to C. coarctatum, exhibited significant relative inhibition effects on 14 out of 15 phytopathogens tested in this study, indicating its broad-spectrum antagonistic effects. Additionally, NSJA2 exhibited excellent salt tolerance. Overall, our study has identified multiple fungi with anti-phytopathogens potential, among which NSJA2 exhibits high potential for practical application. This finding paves the way for further exploration and exploitation of NSJA2 as a promising biocontrol agent.

Regulatory balance between ear rot resistance and grain yield and their breeding applications in maize and other crops

BACKGROUND

Fungi are prevalent pathogens that cause substantial yield losses of major crops. Ear rot (ER), which is primarily induced by Fusarium or Aspergillus species, poses a significant challenge to maize production worldwide. ER resistance is regulated by several small effect quantitative trait loci (QTLs). To date, only a few ER-related genes have been identified that impede molecular breeding efforts to breed ER-resistant maize varieties.

AIM OF REVIEW

Our aim here is to explore the research progress and mine genic resources related to ER resistance, and to propose a regulatory model elucidating the ER-resistant mechanism in maize as well as a trade-off model illustrating how crops balance fungal resistance and grain yield. Key Scientific Concepts of Review: This review presents a comprehensive bibliometric analysis of the research history and current trends in the genetic and molecular regulation underlying ER resistance in maize. Moreover, we analyzed and discovered the genic resources by identifying 162 environmentally stable loci (ESLs) from various independent forward genetics studies as well as 1391 conservatively differentially expressed genes (DEGs) that respond to Fusarium or Aspergillus infection through multi-omics data analysis. Additionally, this review discusses the syntenies found among maize ER, wheat Fusariumhead blight (FHB), and rice Bakanaedisease (RBD) resistance-related loci, along with the significant overlap between fungal resistance loci and reported yield-related loci, thus providing valuable insights into the regulatory mechanisms underlying the trade-offs between yield and defense in crops.

Rapidly Evolved Genes in Three Reaumuria Transcriptomes and Potential Roles of Pentatricopeptide Repeat Superfamily Proteins in Endangerment of R. trigyna

Reaumuria genus (Tamaricaceae) is widely distributed across the desert and semi-desert regions of Northern China, playing a crucial role in the restoration and protection of desert ecosystems. Previous studies mainly focused on the physiological responses to environmental stresses; however, due to the limited availability of genomic information, the underlying mechanism of morphological and ecological differences among the Reaumuria species remains poorly understood. In this study, we presented the first catalog of expressed transcripts for R. kaschgarica, a sympatric species of xerophyte R. soongorica. We further performed the pair-wise transcriptome comparison to determine the conserved and divergent genes among R. soongorica, R. kaschgarica, and the relict recretohalophyte R. trigyna. Annotation of the 600 relatively conserved genes revealed that some common genetic modules are employed by the Reaumuria species to confront with salt and drought stresses in arid environment. Among the 250 genes showing strong signs of positive selection, eight pentatricopeptide repeat (PPR) superfamily protein genes were specifically identified, including seven PPR genes in the R. soongorica vs. R. trigyna comparison and one PPR gene in the R. kaschgarica vs. R. trigyna comparison, while the cyclin D3 gene was found in the R. soongorica vs. R. trigyna comparison. These findings suggest that genetic variations in PPR genes may affect the fertility system or compromise the extent of organelle RNA editing in R. trigyna. The present study provides valuable genomic information for R. kaschgarica and preliminarily reveals the conserved genetic bases for the abiotic stress adaptation and interspecific divergent selection in the Reaumuria species. The rapidly evolved PPR and cyclin D3 genes provide new insights on the endangerment of R. trigyna and the leaf length difference among the Reaumuria species.

Candida albicans PPR proteins are required for the expression of respiratory Complex I subunits

Pentatricopeptide repeat (PPR) proteins bind RNA and are present in mitochondria and chloroplasts of Eukaryota. In fungi, they are responsible for controlling mitochondrial genome expression, mainly on the posttranscriptional level. Candida albicans is a human opportunistic pathogen with a facultative anaerobic metabolism which, unlike the model yeast Saccharomyces cerevisiae, possesses mitochondrially encoded respiratory Complex I (CI) subunits and does not tolerate loss of mtDNA. We characterized the function of 4 PPR proteins of C. albicans that lack orthologs in S. cerevisiae and found that they are required for the expression of mitochondrially encoded CI subunits. We demonstrated that these proteins localize to mitochondria and are essential to maintain the respiratory capacity of cells. Deletion of genes encoding these PPR proteins results in changes in steady-state levels of mitochondrial RNAs and proteins. We demonstrated that C. albicans cells lacking CaPpr4, CaPpr11, and CaPpr13 proteins show no CI assembly, whereas the lack of CaPpr7p results in a decreased CI activity. CaPpr13p is required to maintain the bicistronic NAD4L-NAD5 mRNA, whereas the other 3 PPR proteins are likely involved in translation-related assembly of mitochondrially encoded CI subunits. In addition, we show that CaAep3p, which is an ortholog of ScAep3p, performs the evolutionary conserved function of controlling expression of the ATP8-ATP6 mRNA. We also show that C. albicans cells lacking PPR proteins express a higher level of the inducible alternative oxidase (AOX2) which likely rescues respiratory defects and compensates for oxidative stress.

Restorer of fertility like 30, encoding a mitochondrion-localized pentatricopeptide repeat protein, regulates wood formation in poplar

Nuclear-mitochondrial communication is crucial for plant growth, particularly in the context of cytoplasmic male sterility (CMS) repair mechanisms linked to mitochondrial genome mutations. The restorer of fertility-like (RFL) genes, known for their role in CMS restoration, remain largely unexplored in plant development. In this study, we focused on the evolutionary relationship of RFL family genes in poplar specifically within the dioecious Salicaceae plants. PtoRFL30 was identified to be preferentially expressed in stem vasculature, suggesting a distinct correlation with vascular cambium development. Transgenic poplar plants overexpressing PtoRFL30 exhibited a profound inhibition of vascular cambial activity and xylem development. Conversely, RNA interference-mediated knockdown of PtoRFL30 led to increased wood formation. Importantly, we revealed that PtoRFL30 plays a crucial role in maintaining mitochondrial functional homeostasis. Treatment with mitochondrial activity inhibitors delayed wood development in PtoRFL30-RNAi transgenic plants. Further investigations unveiled significant variations in auxin accumulation levels within vascular tissues of PtoRFL30-transgenic plants. Wood development anomalies resulting from PtoRFL30 overexpression and knockdown were rectified by NAA and NPA treatments, respectively. Our findings underscore the essential role of the PtoRFL30-mediated mitochondrion-auxin signaling module in wood formation, shedding light on the intricate nucleus-organelle communication during secondary vascular development.

The atypical Dof transcriptional factor OsDes1 contributes to stay-green, grain yield, and disease resistance in rice

The regulation of leaf senescence and disease resistance plays a crucial role in determining rice grain yield and quality, which are important to meet the ever-increasing food demands of the world. Here, we identified an atypical Dof transcriptional factor OsDes1 that contributes to the stay-green phenotype, grain yield, and disease resistance in rice. The expression level of OsDes1 is positively associated with stay-green in natural variations of japonica rice, suggesting that OsDes1 would be alternatively used in breeding programs. Mechanistically, OsDes1 targets the promoter of the Rieske FeS protein gene OsPetC to activate its expression and interacts with OsPetC to protect against its degradation, thus promoting stay-green and ultimately improving the grain yield. OsDes1 also binds to the promoter region of defense-related genes, such as OsPR1b, and activates their expression, leading to enhanced disease resistance. These findings offer a potential strategy for breeding rice to enhance grain yield and disease resistance.

A novel PLS-DYW type PPR protein OsASL is essential for chloroplast development in rice

Oryza longistaminata (OL), an AA-genome African wild rice which can propagate clonally via rhizome, is an important germplasm for improvement of Asian cultivated rice, however recessive lethal alleles can hitchhike clonal propagation in heterozygous state. Selfing of OL is difficult due to its self-incompatibility, but simple selfing of hybrid progeny between OL and O. sativa is effective to disclose and eliminate recessive lethal alleles. Here, we identified an exhibited albino-lethal phenotype mutant, from an F2 population between OL and O. sativa, named it albino seedling-lethal (asl). The leaves of asl mutant showed abnormal chloroplast development. The albino characteristics of asl were determined to be governed by a set of recessive nuclear genes through genetic analysis. Map-based cloning experiments found that a single nucleotide variation (G to A) was detected in the exon of OsASL in OL, which causes a premature stop codon. OsASL encodes a PLS-type PPR protein with 12 pentratricopeptide repeat domains, and is translocalized to chloroplasts. Complementation and knockout transgenic experiments further confirmed that OsASL is responsible for the albino-lethal phenotype. Loss-of-function OsASL (i.e. osasl) resulted in devoid of intron splicing of chloroplast RNA atpF, ndhA, rpl2 and rps12, and also RNA editing of ndhB, but facilitates the RNA editing of rpl2 in the plastid. Transcriptome sequencing showed that OsASL was mainly involved in chlorophyll synthesis pathway. The expression of Chlorophyll-associated genes were significantly decreased in asl plants, especially PEP (plastid-encoded RNA polymerase)-mediated genes. Our results suggest that OsASL is crucial for RNA editing, RNA splicing of chloroplast RNA group II genes, and plays an essential role in chloroplast development during early leaf development in rice.

PPR proteins in plants: roles, mechanisms, and prospects for rice research

Pentatricopeptide repeat (PPR) proteins constitute one of the largest protein families in land plants, with over 300 members in various species. Nearly all PPR proteins are nuclear-encoded and targeted to the chloroplast and mitochondria, modulating organellar gene expression by participating in RNA metabolism, including mRNA stability, RNA editing, RNA splicing, and translation initiation. Organelle RNA metabolism significantly influences chloroplast and mitochondria functions, impacting plant photosynthesis, respiration, and environmental responses. Over the past decades, PPR proteins have emerged as a research focus in molecular biology due to their diverse roles throughout plant life. This review summarizes recent progress in understanding the roles and molecular mechanisms of PPR proteins, emphasizing their functions in fertility, abiotic and biotic stress, grain quality, and chloroplast development in rice. Furthermore, we discuss prospects for PPR family research in rice, aiming to provide a theoretical foundation for future investigations and applications.

Integration of transcriptomics, metabolomics, and hormone analysis revealed the formation of lesion spots inhibited by GA and CTK was related to cell death and disease resistance in bread wheat (Triticum aestivum L.)

BACKGROUND

Wheat is one of the important grain crops in the world. The formation of lesion spots related to cell death is involved in disease resistance, whereas the regulatory pathway of lesion spot production and resistance mechanism to pathogens in wheat is largely unknown.

RESULTS

In this study, a pair of NILs (NIL-Lm5W and NIL-Lm5M) was constructed from the BC1F4 population by the wheat lesion mimic mutant MC21 and its wild genotype Chuannong 16. The formation of lesion spots in NIL-Lm5M significantly increased its resistance to stripe rust, and NIL-Lm5M showed superiour agronomic traits than NIL-Lm5W under stripe rust infection.Whereafter, the NILs were subjected to transcriptomic (stage N: no spots; stage S, only a few spots; and stage M, numerous spots), metabolomic (stage N and S), and hormone analysis (stage S), with samples taken from normal plants in the field. Transcriptomic analysis showed that the differentially expressed genes were enriched in plant-pathogen interaction, and defense-related genes were significantly upregulated following the formation of lesion spots. Metabolomic analysis showed that the differentially accumulated metabolites were enriched in energy metabolism, including amino acid metabolism, carbohydrate metabolism, and lipid metabolism. Correlation network diagrams of transcriptomic and metabolomic showed that they were both enriched in energy metabolism. Additionally, the contents of gibberellin A7, cis-Zeatin, and abscisic acid were decreased in leaves upon lesion spot formation, whereas the lesion spots in NIL-Lm5M leaves were restrained by spaying GA and cytokinin (CTK, trans-zeatin) in the field.

CONCLUSION

The formation of lesion spots can result in cell death and enhance strip rust resistance by protein degradation pathway and defense-related genes overexpression in wheat. Besides, the formation of lesion spots was significantly affected by GA and CTK. Altogether, these results may contribute to the understanding of lesion spot formation in wheat and laid a foundation for regulating the resistance mechanism to stripe rust.

Genome-wide identification of ZmMYC2 binding sites and target genes in maize

BACKGROUND

Jasmonate (JA) is the important phytohormone to regulate plant growth and adaption to stress signals. MYC2, an bHLH transcription factor, is the master regulator of JA signaling. Although MYC2 in maize has been identified, its function remains to be clarified.

RESULTS

To understand the function and regulatory mechanism of MYC2 in maize, the joint analysis of DAP-seq and RNA-seq is conducted to identify the binding sites and target genes of ZmMYC2. A total of 3183 genes are detected both in DAP-seq and RNA-seq data, potentially as the directly regulating genes of ZmMYC2. These genes are involved in various biological processes including plant growth and stress response. Besides the classic cis-elements like the G-box and E-box that are bound by MYC2, some new motifs are also revealed to be recognized by ZmMYC2, such as nGCATGCAnn, AAAAAAAA, CACGTGCGTGCG. The binding sites of many ZmMYC2 regulating genes are identified by IGV-sRNA.

CONCLUSIONS

All together, abundant target genes of ZmMYC2 are characterized with their binding sites, providing the basis to construct the regulatory network of ZmMYC2 and better understanding for JA signaling in maize.

Unraveling the genetics of heat tolerance in chickpea landraces (Cicer arietinum L.) using genome-wide association studies

Chickpea, being an important grain legume crop, is often confronted with the adverse effects of high temperatures at the reproductive stage of crop growth, drastically affecting yield and overall productivity. The current study deals with an extensive evaluation of chickpea genotypes, focusing on the traits associated with yield and their response to heat stress. Notably, we observed significant variations for these traits under both normal and high-temperature conditions, forming a robust basis for genetic research and breeding initiatives. Furthermore, the study revealed that yield-related traits exhibited high heritability, suggesting their potential suitability for marker-assisted selection. We carried out single-nucleotide polymorphism (SNP) genotyping using the genotyping-by-sequencing (GBS) method for a genome-wide association study (GWAS). Overall, 27 marker-trait associations (MTAs) linked to yield-related traits, among which we identified five common MTAs displaying pleiotropic effects after applying a stringent Bonferroni-corrected p-value threshold of <0.05 [-log10(p) > 4.95] using the BLINK (Bayesian-information and linkage-disequilibrium iteratively nested keyway) model. Through an in-depth in silico analysis of these markers against the CDC Frontier v1 reference genome, we discovered that the majority of the SNPs were located at or in proximity to gene-coding regions. We further explored candidate genes situated near these MTAs, shedding light on the molecular mechanisms governing heat stress tolerance and yield enhancement in chickpeas such as indole-3-acetic acid-amido synthetase GH3.1 with GH3 auxin-responsive promoter and pentatricopeptide repeat-containing protein, etc. The harvest index (HI) trait was associated with marker Ca3:37444451 encoding aspartic proteinase ortholog sequence of Oryza sativa subsp. japonica and Medicago truncatula, which is known for contributing to heat stress tolerance. These identified MTAs and associated candidate genes may serve as valuable assets for breeding programs dedicated to tailoring chickpea varieties resilient to heat stress and climate change.

Mutation in Arabidopsis mitochondrial Pentatricopeptide repeat 40 gene affects tolerance to water deficit

MAIN CONCLUSION

The Arabidopsis Pentatricopeptide repeat 40 (PPR40) insertion mutants have increased tolerance to water deficit compared to wild-type plants. Tolerance is likely the consequence of ABA hypersensitivity of the mutants. Plant growth and development depend on multiple environmental factors whose alterations can disrupt plant homeostasis and trigger complex molecular and physiological responses. Water deficit is one of the factors which can seriously restrict plant growth and viability. Mitochondria play an important role in cellular metabolism, energy production, and redox homeostasis. During drought and salinity stress, mitochondrial dysfunction can lead to ROS overproduction and oxidative stress, affecting plant growth and survival. Alternative oxidases (AOXs) and stabilization of mitochondrial electron transport chain help mitigate ROS damage. The mitochondrial Pentatricopeptide repeat 40 (PPR40) protein was implicated in stress regulation as ppr40 mutants were found to be hypersensitive to ABA and high salinity during germination. This study investigated the tolerance of the knockout ppr40-1 and knockdown ppr40-2 mutants to water deprivation. Our results show that these mutants display an enhanced tolerance to water deficit. The mutants had higher relative water content, reduced level of oxidative damage, and better photosynthetic parameters in water-limited conditions compared to wild-type plants. ppr40 mutants had considerable differences in metabolic profiles and expression of a number of stress-related genes, suggesting important metabolic reprogramming. Tolerance to water deficit was also manifested in higher survival rates and alleviated growth reduction when watering was suspended. Enhanced sensitivity to ABA and fast stomata closure was suggested to lead to improved capacity for water conservation in such environment. Overall, this study highlights the importance of mitochondrial functions and in particular PPR40 in plant responses to abiotic stress, particularly drought.

Importance of pre-mRNA splicing and its study tools in plants

Alternative splicing (AS) significantly enriches the diversity of transcriptomes and proteomes, playing a pivotal role in the physiology and development of eukaryotic organisms. With the continuous advancement of high-throughput sequencing technologies, an increasing number of novel transcript isoforms, along with factors related to splicing and their associated functions, are being unveiled. In this review, we succinctly summarize and compare the different splicing mechanisms across prokaryotes and eukaryotes. Furthermore, we provide an extensive overview of the recent progress in various studies on AS covering different developmental stages in diverse plant species and in response to various abiotic stresses. Additionally, we discuss modern techniques for studying the functions and quantification of AS transcripts, as well as their protein products. By integrating genetic studies, quantitative methods, and high-throughput omics techniques, we can discover novel transcript isoforms and functional splicing factors, thereby enhancing our understanding of the roles of various splicing modes in different plant species.

Disruption of the Novel Small Protein RBR7 Leads to Enhanced Plant Resistance to Blast Disease

Plant disease is a threat to global food security. Breeding crops carrying broad-spectrum resistance loci is an effective way to control infectious disease. Disease-resistant mutants are valuable resources for deciphering the underlying mechanisms of plant immunity and could provide genetic loci to generate disease-resistant crops. Here, we identified a rice mutant, rbr7 (rice blast resistance 7), that confers resistance against different strains of Magnaporthe oryzae. Disease-mimicking necrotic lesions started to appear on the leaves of rbr7 four weeks after sowing. Histochemical analysis revealed reactive oxygen species accumulation and cell death accompanied by spontaneous lesion formation in rbr7. Map-based cloning and bulk segregation analysis showed a 2855 bp fragment deletion on chromosome 5, leading to the disruption of the LOC_Os05g28480-coding protein. Transgenic rbr7 complementation plants showed compromised resistance to rice blast, indicating that LOC_Os05g28480, or Rbr7, regulates the rice immune response. Rbr7 encodes a small protein of unknown function with 85 amino acids. Transcriptomic analysis revealed that disruption of RBR7 led to the upregulation of genes responding to salicylic acid, systemic acquired resistance and pathogenesis-related genes. Taken together, our findings reveal insights into a novel small protein involved in regulating plant resistance to rice blast and provide a potential target for crop breeding.

Genome wide association study of genes controlling resistance to Didymella rabiei Pathotype IV through genotyping by sequencing in chickpeas (Cicer arietinum)

Ascochyta blight (AB) is a major disease in chickpeas (Cicer arietinum L.) that can cause a yield loss of up to 100%. Chickpea germplasm collections at the center of origin offer great potential to discover novel sources of resistance to pests and diseases. Herein, 189 Cicer arietinum samples were genotyped via genotyping by sequencing. This chickpea collection was phenotyped for resistance to an aggressive Turkish Didymella rabiei Pathotype IV isolate. Genome-wide association studies based on different models revealed 19 single nucleotide polymorphism (SNP) associations on chromosomes 1, 2, 3, 4, 7, and 8. Although eight of these SNPs have been previously reported, to the best of our knowledge, the remaining ten were associated with AB resistance for the first time. The regions identified in this study can be addressed in future studies to reveal the genetic mechanism underlying AB resistance and can also be utilized in chickpea breeding programs to improve AB resistance in new chickpea varieties.

High-resolution mapping of SrTm4, a recessive resistance gene to wheat stem rust

KEY MESSAGE

The diploid wheat recessive stem rust resistance gene SrTm4 was fine-mapped to a 754-kb region on chromosome arm 2AmL and potential candidate genes were identified. Race Ug99 of Puccinia graminis f. sp. tritici (Pgt), the causal agent of wheat stem (or black) rust is one of the most serious threats to global wheat production. The identification, mapping, and deployment of effective stem rust resistance (Sr) genes are critical to reduce this threat. In this study, we generated SrTm4 monogenic lines and found that this gene confers resistance to North American and Chinese Pgt races. Using a large mapping population (9522 gametes), we mapped SrTm4 within a 0.06 cM interval flanked by marker loci CS4211 and 130K1519, which corresponds to a 1.0-Mb region in the Chinese Spring reference genome v2.1. A physical map of the SrTm4 region was constructed with 11 overlapping BACs from the resistant Triticum monococcum PI 306540. Comparison of the 754-kb physical map with the genomic sequence of Chinese Spring and a discontinuous BAC sequence of DV92 revealed a 593-kb chromosomal inversion in PI 306540. Within the candidate region, we identified an L-type lectin-domain containing receptor kinase (LLK1), which was disrupted by the proximal inversion breakpoint, as a potential candidate gene. Two diagnostic dominant markers were developed to detect the inversion breakpoints. In a survey of T. monococcum accessions, we identified 10 domesticated T. monococcum subsp. monococcum genotypes, mainly from the Balkans, carrying the inversion and showing similar mesothetic resistant infection types against Pgt races. The high-density map and tightly linked molecular markers developed in this study are useful tools to accelerate the deployment of SrTm4-mediated resistance in wheat breeding programs.

Rice ubiquitin-conjugating enzyme OsUbc13 negatively regulates immunity against pathogens by enhancing the activity of OsSnRK1a

Ubc13 is required for Lys63-linked polyubiquitination and innate immune responses in mammals, but its functions in plant immunity still remain largely unknown. Here, we used molecular biological, pathological, biochemical, and genetic approaches to evaluate the roles of rice OsUbc13 in response to pathogens. The OsUbc13-RNA interference (RNAi) lines with lesion mimic phenotypes displayed a significant increase in the accumulation of flg22- and chitin-induced reactive oxygen species, and in defence-related genes expression or hormones as well as resistance to Magnaporthe oryzae and Xanthomonas oryzae pv oryzae. Strikingly, OsUbc13 directly interacts with OsSnRK1a, which is the α catalytic subunit of SnRK1 (sucrose non-fermenting-1-related protein kinase-1) and acts as a positive regulator of broad-spectrum disease resistance in rice. In the OsUbc13-RNAi plants, although the protein level of OsSnRK1a did not change, its activity and ABA sensitivity were obviously enhanced, and the K63-linked polyubiquitination was weaker than that of wild-type Dongjin (DJ). Overexpression of the deubiquitinase-encoding gene OsOTUB1.1 produced similar effects with inhibition of OsUbc13 in affecting immunity responses, M. oryzae resistance, OsSnRK1a ubiquitination, and OsSnRK1a activity. Furthermore, re-interfering with OsSnRK1a in one OsUbc13-RNAi line (Ri-3) partially restored its M. oryzae resistance to a level between those of Ri-3 and DJ. Our data demonstrate OsUbc13 negatively regulates immunity against pathogens by enhancing the activity of OsSnRK1a.

A ubiquitin-specific protease functions in regulating cell death and immune responses in rice

Ubiquitin-specific proteases (UBPs) process deubiquitination in eukaryotic organisms and are widely involved in plant development and responses to environmental stress. However, their role in cell death and plant immunity remains largely unknown. Here, we identified a rice lesion mimic mutant (LMM) and cloned its causative gene, LMM22. Both dysfunction and overexpression of LMM22 gave rise to the hypersensitive response-like cell death, reactive oxygen species bursts, and activated defence responses. LMM22 encodes an active UBP that is localised to the endoplasmic reticulum (ER) and displays a constitutive expression pattern in rice. LMM22 interacts with SPOTTED LEAF 35 (SPL35), a coupling of ubiquitin conjugation to ER degradation domain-containing protein that is known to participate in ubiquitination and the regulation of cell death and disease response in rice. Additional analyses suggest that LMM22 can positively regulate and stabilise the abundance of SPL35 protein likely through its deubiquitination activity. These data therefore improve our understanding of the function of UBP in rice innate immune responses by demonstrating that LMM22 functions as a critical regulator of SPL35 in cell death and disease resistance.

Towards Marker-Assisted Breeding for Black Rot Bunch Resistance: Identification of a Major QTL in the Grapevine Cultivar 'Merzling'

Black rot (BR), caused by Guignardia bidwellii, is an emergent fungal disease threatening viticulture and affecting several mildew-tolerant varieties. However, its genetic bases are not fully dissected yet. For this purpose, a segregating population derived from the cross 'Merzling' (hybrid, resistant) × 'Teroldego' (V. vinifera, susceptible) was evaluated for BR resistance at the shoot and bunch level. The progeny was genotyped with the GrapeReSeq Illumina 20K SNPchip, and 7175 SNPs were combined with 194 SSRs to generate a high-density linkage map of 1677 cM. The QTL analysis based on shoot trials confirmed the previously identified Resistance to Guignardia bidwellii (Rgb)1 locus on chromosome 14, which explained up to 29.2% of the phenotypic variance, reducing the genomic interval from 2.4 to 0.7 Mb. Upstream of Rgb1, this study revealed a new QTL explaining up to 79.9% of the variance for bunch resistance, designated Rgb3. The physical region encompassing the two QTLs does not underlie annotated resistance (R)-genes. The Rgb1 locus resulted enriched in genes belonging to phloem dynamics and mitochondrial proton transfer, while Rgb3 presented a cluster of pathogenesis-related Germin-like protein genes, promoters of the programmed cell death. These outcomes suggest a strong involvement of mitochondrial oxidative burst and phloem occlusion in BR resistance mechanisms and provide new molecular tools for grapevine marker-assisted breeding.

Genome-Wide Association Study (GWAS) of White Mold Resistance in Snap Bean

White mold can result in snap bean yield losses of 90 to 100% when field conditions favor the pathogen. A genome-wide association study (GWAS) was conducted to detect loci significantly associated with white mold resistance in a panel of snap bean (Phaseolus vulgaris L.) cultivars. Two populations of snap bean were used in this study. The first population was the BeanCAP (Coordinated Agriculture Project) Snap Bean Diversity Panel (SBDP) (n = 136), and the second population was the Snap Bean Association Panel (SnAP) (n = 378). SBDP was evaluated for white mold reaction in the field in 2012 and 2013, and SnAP was screened in a greenhouse only using the seedling straw test in 2016. Two reference genomes representing the Andean and Middle American centers of domestication were utilized to align the genotyping-by-sequencing (GBS) data. A GWAS was performed using FarmCPU with one principal component after comparing five models. Thirty-four single-nucleotide polymorphisms (SNPs) significantly associated with white mold resistance were detected. Eleven significant SNPs were identified by the seedling straw test, and 23 significant SNPs were identified by field data. Fifteen SNPs were identified within a 100 kb window containing pentatricopeptide repeat (PPR)-encoding genes, and eleven were close to leucine-rich repeat (LRR)-encoding genes, suggesting that these two classes are of outsized importance for snap bean resistance to white mold.

The PPR-Domain Protein SOAR1 Regulates Salt Tolerance in Rice

Previous studies in Arabidopsis reported that the PPR protein SOAR1 plays critical roles in plant response to salt stress. In this study, we reported that expression of the Arabidopsis SOAR1 (AtSOAR1) in rice significantly enhanced salt tolerance at seedling growth stage and promoted grain productivity under salt stress without affecting plant productivity under non-stressful conditions. The transgenic rice lines expressing AtSOAR1 exhibited increased ABA sensitivity in ABA-induced inhibition of seedling growth, and showed altered transcription and splicing of numerous genes associated with salt stress, which may explain salt tolerance of the transgenic plants. Further, we overexpressed the homologous gene of SOAR1 in rice, OsSOAR1, and showed that transgenic plants overexpressing OsSOAR1 enhanced salt tolerance at seedling growth stage. Five salt- and other abiotic stress-induced SOAR1-like PPRs were also identified. These data showed that the SOAR1-like PPR proteins are positively involved in plant response to salt stress and may be used for crop improvement in rice under salinity conditions through transgenic manipulation.

Mitochondrial functions in plant immunity

Mitochondria are energy factories of cells and are important for intracellular interactions with other organelles. Emerging evidence indicates that mitochondria play essential roles in the response to pathogen infection. During infection, pathogens deliver numerous enzymes and effectors into host cells, and some of these effectors target mitochondria, altering mitochondrial morphology, metabolism, and functions. To defend against pathogen attack, mitochondria are actively involved in changing intracellular metabolism, hormone-mediated signaling, and signal transduction, producing reactive oxygen species and reactive nitrogen species and triggering programmed cell death. Additionally, mitochondria coordinate with other organelles to integrate and amplify diverse immune signals. In this review, we summarize recent advances in understanding how mitochondria function in plant immunity and how pathogens target mitochondria for host defense suppression.

A dominant gene Ihrl1 is tightly linked to and inhibits the gene Ndhrl1 mediating nitrogen-dependent hypersensitive reaction-like phenotype in wheat

Identification and mapping of an inhibitor of Ndhrl1 mediating nitrogen-dependent hypersensitive reaction-like phenotype in wheat. Hypersensitive reaction-like (HRL) traits are characteristic of spontaneous lesions including yellowish spots, brown spots or white-stripe that appeared randomly and dispersedly on all the leaves in the absence of plant pathogens. Our previous studies have shown that the wheat line P7001 showed an HRL trait at low nitrogen supply, and this trait was controlled by the gene Ndhrl1 (Nitrogen-dependent hypersensitive reaction-like 1). In order to investigate the robustness of the trait expression mediated by Ndhrl1 under different genetic backgrounds, seven genetic populations, with P7001 being the common female parent, were constructed and analyzed. F₁ plants from six of the seven combinations showed HRL trait and Ndhrl1 segregated in a dominant way of HRL: non-HRL = 3:1 in the six populations (F₂). Exceptionally, the F₁ plants of P7001/Fielder combination showed non-HRL trait and HRL trait in the F₂ population showed a contrasting recessive segregation ratio of HRL: non-HRL = 1:3, suggesting Fielder may have another HRL-related gene. Using 55 K SNP array and PCR-based markers, the HRL-related gene in Fielder was mapped to an interval of 5.63-12.91 Mb on the short arm of chromosome 2B with the flanking markers Yzu660R075552 and Yzu660F075941. A recombinant with genomic region of Fielder at Ndhrl1 locus showing HRL trait demonstrated that Fielder also harbored Ndhrl1 same as P7001. Thus, Fielder carries a single dominant suppressor of Ndhrl1, designated as Ihrl1 (Inhibitor of hypersensitive reaction-like). Interestingly, Ihrl1 is tightly linked to Ndhrl1 and may be also involved in nitrogen metabolic and (or) signaling pathways.

A mitochondrial RNA processing protein mediates plant immunity to a broad spectrum of pathogens by modulating the mitochondrial oxidative burst

Mitochondrial function depends on the RNA processing of mitochondrial gene transcripts by nucleus-encoded proteins. This posttranscriptional processing involves the large group of nuclear-encoded pentatricopeptide repeat (PPR) proteins. Mitochondrial processes represent a crucial part in animal immunity, but whether mitochondria play similar roles in plants remains unclear. Here, we report the identification of RESISTANCE TO PHYTOPHTHORA PARASITICA 7 (AtRTP7), a P-type PPR protein, in Arabidopsis thaliana and its conserved function in immunity to diverse pathogens across distantly related plant species. RTP7 affects the levels of mitochondrial reactive oxygen species (mROS) by participating in RNA splicing of nad7, which encodes a critical subunit of the mitochondrial respiratory chain Complex I, the largest of the four major components of the mitochondrial oxidative phosphorylation system. The enhanced resistance of rtp7 plants to Phytophthora parasitica is dependent on an elevated mROS burst, but might be independent from the ROS burst associated with plasma membrane-localized NADPH oxidases. Our study reveals the immune function of RTP7 and the defective processing of Complex I subunits in rtp7 plants resulted in enhanced resistance to both biotrophic and necrotrophic pathogens without affecting overall plant development.

Rice Lesion Mimic Gene Cloning and Association Analysis for Disease Resistance

Lesion mimic mutants refer to a class of mutants that naturally form necrotic lesions similar to allergic reactions on leaves in the absence of significant stress or damage and without being harmed by pathogens. Mutations in most lesion mimic genes, such as OsACL-A2 and OsSCYL2, can enhance mutants’ resistance to pathogens. Lesion mimic mutants are ideal materials for studying programmed cell death (PCD) and plant defense mechanisms. Studying the genes responsible for the rice disease-like phenotype is of great significance for understanding the disease resistance mechanism of rice. In this paper, the nomenclature, occurrence mechanism, genetic characteristics, regulatory pathways, and the research progress on the cloning and disease resistance of rice lesion mimic mutant genes were reviewed, in order to further analyze the various lesion mimic mutants of rice. The mechanism lays a theoretical foundation and provides a reference for rice breeding.

The Rice Malectin Regulates Plant Cell Death and Disease Resistance by Participating in Glycoprotein Quality Control

In animals, malectin is well known to play an essential role in endoplasmic reticulum quality control (ERQC) by interacting with ribophorin I, one unit of the oligosaccharyltransferase (OST) complex. However, the functions of malectin in plants remain largely unknown. Here, we demonstrate the rice OsMLD1 is an ER- and Golgi-associated malectin protein and physically interacts with rice homolog of ribophorin I (OsRpn1), and its disruption leads to spontaneous lesion mimic lesions, enhanced disease resistance, and prolonged ER stress. In addition, there are many more N-glycosites and N-glycoproteins identified from the mld1 mutant than wildtype. Furthermore, OsSERK1 and OsSERK2, which have more N-glycosites in mld1, were demonstrated to interact with OsMLD1. OsMLD1 can suppress OsSERK1- or OsSERK2-induced cell death. Thus, OsMLD1 may play a similar role to its mammalian homologs in glycoprotein quality control, thereby regulating cell death and immunity of rice, which uncovers the function of malectin in plants.

Tryptamine 5-Hydroxylase Is Required for Suppression of Cell Death and Uncontrolled Defense Activation in Rice

Lesion-mimic mutants are useful materials to dissect mechanisms controlling programmed cell death (PCD) and defense response in plants. Although dozens of lesion-mimic mutant genes have been identified in plants, the molecular mechanisms underlying PCD and defense response remain to be extensively elucidated. Here, we identified a rice lesion mimic mutant, named lesion mimic 42 (lm42), from an ethylmethylsulfone (EMS)-induced mutant population. The lm42 mutant displayed flame-red spots on the leaves and sheaths at the 3-leaf developmental stage and exhibited impaired photosynthetic capacity with decreased chlorophyll content and decomposed chloroplast thylakoids. The lesion development of lm42 was light- and temperature-dependent. We identified a single base mutation (T38A), changing a Leu to Gln, in the first exon of LOC_Os12g16720 (LM42), which encodes a tryptamine 5-hydroxylase, by map-based cloning. We carried out transgenic complementation to confirm that this mutation caused the lm42 phenotype. We further knocked out the LM42 gene by CRISPR/Cas9 to recreate the lm42 phenotype. LM42 is highly expressed in leaves, leaf sheaths and roots. Loss-of-function of LM42 activated expression of ROS-generating genes and inhibited expression of ROS-scavenging genes, leading to ROS accumulation and eventually cell death. Furthermore, its disruption induced expression of defense-response genes and enhanced host resistance to both fungal pathogen Magnaporthe oryzae and bacterial pathogen Xanthomonas oryzae pv. oryzae. Our transcriptomic data suggested that the way lm42 led to lesion-mimic was probably by affecting ribosome development. Overall, our results demonstrate that tryptamine 5-hydroxylase-coding gene LM42 is required for suppression of cell death and uncontrolled activation of defense responses in rice.

Disruption of OsPHD1, Encoding a UDP-Glucose Epimerase, Causes JA Accumulation and Enhanced Bacterial Blight Resistance in Rice

Lesion mimic mutants (LMMs) have been widely used in experiments in recent years for studying plant physiological mechanisms underlying programmed cell death (PCD) and defense responses. Here, we identified a lesion mimic mutant, lm212-1, which cloned the causal gene by a map-based cloning strategy, and verified this by complementation. The causal gene, OsPHD1, encodes a UDP-glucose epimerase (UGE), and the OsPHD1 was located in the chloroplast. OsPHD1 was constitutively expressed in all organs, with higher expression in leaves and other green tissues. lm212-1 exhibited decreased chlorophyll content, and the chloroplast structure was destroyed. Histochemistry results indicated that H₂O₂ is highly accumulated and cell death is occurred around the lesions in lm212-1. Compared to the wild type, expression levels of defense-related genes were up-regulated, and resistance to bacterial pathogens Xanthomonas oryzae pv. oryzae (Xoo) was enhanced, indicating that the defense response was activated in lm212-1, ROS production was induced by flg22, and chitin treatment also showed the same result. Jasmonic acid (JA) and methyl jasmonate (MeJA) increased, and the JA signaling pathways appeared to be disordered in lm212-1. Additionally, the overexpression lines showed the same phenotype as the wild type. Overall, our findings demonstrate that OsPHD1 is involved in the regulation of PCD and defense response in rice.

Fine mapping and candidate gene analysis of qGSN5, a novel quantitative trait locus coordinating grain size and grain number in rice

KEY MESSAGE: qGSN5, a novel quantitative trait locus coordinating grain size and grain number in rice, was fine-mapped to an 85.60-kb region. GS3 may be a suppressor of qGSN5. Grain size and grain number are two factors that directly determine rice grain yield; however, the underlying genetic mechanisms are complicated and remain largely unclear. In this study, a chromosome segment substitution line (CSSL), CSSL28, which showed increased grain size and decreased grain number per panicle, was identified in a set of CSSLs derived from a cross between 93-11 (recipient) and Nipponbare (donor). Four substitution segments were identified in CSSL28, and the substitution segment located on chromosome 5 was responsible for the phenotypes of CSSL28. Thus, we defined this quantitative trait locus (QTL) as grain size and grain number 5 (qGSN5). Cytological and quantitative PCR analysis showed that qGSN5 regulates the development of the spikelet hull by affecting cell proliferation. Genetic analysis showed that qGSN5 is a semi-dominant locus regulating grain size and grain number. Through map-based cloning and overlapping substitution segment analysis, qGSN5 was finally delimited to an 85.60-kb region. Based on sequence and quantitative PCR analysis, Os05g47510, which encodes a P-type pentatricopeptide repeat protein, is the most likely candidate gene for qGSN5. Pyramiding analysis showed that the effect of qGSN5 was significantly lower in the presence of a functional GS3 gene, indicating that GS3 may be a suppressor of qGSN5. In addition, we found that qGSN5 could improve the grain shape of hybrid rice. Together, our results lay the foundation for cloning a novel QTL coordinating grain size and grain number in rice and provide a good genetic material for long-grain hybrid rice breeding.

Combining GWAS, Genome-Wide Domestication and a Transcriptomic Analysis Reveals the Loci and Natural Alleles of Salt Tolerance in Rice (Oryza sativa L.)

Soil salinity poses a serious threat to the sustainable production of rice (Oryza sativa L.) throughout the world. Thus, the detection of loci and alleles responsible for salt tolerance is fundamental to accelerating the improvement of rice and producing the resilient varieties that will ensure future harvests. In this study, we collected a set of 191 mini-core rice populations from around the world, evaluated their salt tolerance based on plant growth and development phenotypes at the seedling stage, and divided a standard evaluation score (SES) of visual salt injury into five different grades. We used ∼3.82 million single nucleotide polymorphisms (SNPs) to identify 155 significant SNPs and 275 genes associated with salt sensitivity based on a genome-wide association study (GWAS) of SES. In particular, two candidate genes, ZFP179 and OsDSR2, were associated with salt tolerance, and OsHKT1;1 was co-detected in the entire GWAS of all the panels and indica. Additionally, we investigated the transcriptional changes in cultivars 93-11 and PA64s under normal and salinity stress conditions and found 517 co-upregulated and 223 co-downregulated genes. These differentially expressed genes (DEGs) were highly enriched in "response to chemical" and "stress" based on the gene ontology enrichment analysis. Notably, 30 candidate genes that were associated with the salt tolerance analysis were obtained by integrating GWAS and transcriptomic DEG analyses, including 13 cloned genes that had no reports of tolerance to salt and 17 candidate genes whose functions were unknown. To further explore these genes and their alleles, we performed haplotype analysis, genome-wide domestication detection, and transcriptome analysis to breed improved varieties. This data and the genetic resources provided will be valuable for the development of salt tolerant rice varieties.

Functions of PPR Proteins in Plant Growth and Development

Pentatricopeptide repeat (PPR) proteins form a large protein family in land plants, with hundreds of different members in angiosperms. In the last decade, a number of studies have shown that PPR proteins are sequence-specific RNA-binding proteins involved in multiple aspects of plant organellar RNA processing, and perform numerous functions in plants throughout their life cycle. Recently, computational and structural studies have provided new insights into the working mechanisms of PPR proteins in RNA recognition and cytidine deamination. In this review, we summarized the research progress on the functions of PPR proteins in plant growth and development, with a particular focus on their effects on cytoplasmic male sterility, stress responses, and seed development. We also documented the molecular mechanisms of PPR proteins in mediating RNA processing in plant mitochondria and chloroplasts.