A natural allele of OsMS1 responds to temperature changes and confers thermosensitive genic male sterility

Advancements in hybrid rice production: improvements in male sterility and synthetic apomixis for sustainable agriculture

Rice serves as a staple food for approximately half of the world's population, and enhanced yields from hybrid rice play a crucial role in ensuring food security and augmenting incomes. However, the annual purchase and high cost of hybrid seeds hinder widespread hybrid rice adoption. In this review, we discuss hybrid seed production strategies based on molecular mechanisms along with biotechnological techniques employed for production and future prospects. Male-sterile lines are pivotal in hybrid seed production, with ongoing developments markedly advancing this process. Initially, cytoplasmic male-sterile lines facilitated three-line hybrid seed production. Subsequent innovations, including environmentally responsive gene-based and biotechnology-driven male-sterile lines, enabled two-line hybrid rice production. Ongoing research is focusing on implementing a one-line hybrid seed production method using apomixis, driving innovation in hybrid seed production. Overall, advancements in male-sterile lines and synthetic apomixis present promising avenues for improving the efficiency and sustainability of hybrid rice production. These developments highlight the critical need for continued research and concerted efforts to address global food security challenges.

ALBA3 maintains male fertility under heat stress in plants

Heat stress (HS) at the reproductive stage detrimentally affects crop yields and seed quality. However, the molecular mechanisms that protect reproductive processes in plants under HS remain largely unknown. Here, we report that Acetylation Lowers Binding Affinity 3 (ALBA3) is crucial for safeguarding male fertility against HS in Arabidopsis. ALBA3 is highly expressed in pollen, and ALBA3 is localized in the cytoplasm of both sperm and vegetative cells. Mutants lacking functional ALBA3 exhibit hypersensitivity to HS, with reduced silique length and fertility due to defects in pollen germination, pollination, pollen tube growth, and fertilization under HS. ALBA3 binds and stabilizes a subset of messenger RNAs (mRNAs) essential for pollen function, thereby protecting male fertility. Two residues in the Alba domain, K46 and L90, are critical for ALBA3's ability to bind and stabilize mRNAs and are necessary for its proper function. Interestingly, the loss of rice ALBA3 also leads to severe pollen abortion and male sterility under HS, highlighting the conserved role of ALBA3 in protecting male fertility across plant species. This study uncovers a conserved mechanism by which ALBA3 safeguards male fertility during HS by stabilizing specific mRNAs crucial for pollen function.

Decoding the transcriptional regulatory mechanisms of basic helix-loop-helix transcription factors for fine-tuning target genes in rice

BACKGROUND

In the intricate landscape of gene regulation, basic helix-loop-helix (bHLH) transcription factors (TFs) play a pivotal role in controlling gene expression across various biological processes in plants. The bHLH domain, about 60 amino acids long, consists of a DNA-binding basic region and a dimerization helix-loop-helix region. In rice, 188 bHLH proteins are encoded and more than 90 functionally characterized. To finely regulate the expression of various target genes, bHLH TFs engage multiple transcriptional regulatory mechanisms.

AIM OF REVIEW

The aim of this review is to provide a comprehensive understanding of the diverse transcriptional regulatory mechanisms of bHLH TFs in rice. KEY SCIENTIFIC CONCEPTS OF REVIEW: bHLH TFs engage the diverse transcriptional regulatory mechanisms, including spatiotemporal expression, the formation of inhibitory complexes, and the integration multiple signaling pathways. Additionally, the ability to switch interaction partners provides flexibility in target site recognition, allowing bHLH proteins regulate a wide range of biological processes, from basic cellular functions to complex developmental pathways. Understanding of multiple transcriptional regulatory mechanisms of bHLH TFs can provide key insights for improving crop traits, such as stress resistance and growth efficiency, which are crucial for enhancing agricultural productivity in the future.

Deciphering the Vulnerability of Pollen to Heat Stress for Securing Crop Yields in a Warming Climate

Climate change is leading to more frequent and severe extreme temperature events, negatively impacting agricultural productivity and threatening global food security. Plant reproduction, the process fundamental to crop yield, is highly susceptible to heatwaves, which disrupt pollen development and ultimately affect seed-set and crop yields. Recent research has increasingly focused on understanding how pollen grains from various crops react to heat stress at the molecular and cellular levels. This surge in interest over the last decade has been driven by advances in genomic technologies, such as single-cell RNA sequencing, which holds significant potential for revealing the underlying regulatory reprogramming triggered by heat stress throughout the various stages of pollen development. This review focuses on how heat stress affects gene regulatory networks, including the heat stress response, the unfolded protein response, and autophagy, and discusses the impact of these changes on various stages of pollen development. It highlights the potential of pollen selection as a key strategy for improving heat tolerance in crops by leveraging the genetic variability among pollen grains. Additionally, genome-wide association studies and population screenings have shed light on the genetic underpinnings of traits in major crops that respond to high temperatures during male reproductive stages. Gene-editing tools like CRISPR/Cas systems could facilitate precise genetic modifications to boost pollen heat resilience. The information covered in this review is valuable for selecting traits and employing molecular genetic approaches to develop heat-tolerant genotypes.

Decoupling the pleiotropic effects of VRT-A2 during reproductive development enhances wheat grain length and weight

VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (VRT-A2) is a subspecies-forming gene that confers the long-glume and large-grain traits of tetraploid Polish wheat (Triticum polonicum; AABB) and hexaploid Xinjiang rice wheat (T. petropavlovskyi; AABBDD). Transcriptional activation of VRT-A2 due to a natural sequence variation in its Intron-1 region significantly enhances grain weight but also causes some basal spikelets to fail to completely develop, thus decreasing grain number per spike and yield. This yield penalty has presented a challenge for the use of VRT-A2 in breeding high-yield wheat. Here, we report the characterization of 2 regulatory modules that fine-tune VRT-A2 expression in bread wheat (T. aestivum): (i) the APETALA2/Ethylene Responsive Factor (AP2/ERF)-type transcription factor MULTI-FLORET SPIKELET1 (TaMFS1) represses VRT-A2 expression by recruiting a transcriptional corepressor and a histone deacetylase and (ii) the STRUCTURE-SPECIFIC RECOGNITION PROTEIN 1 (TaSSRP1) facilitates VRT-A2 activation by assembling Mediator and further RNA polymerase II. Deleting TaMFS1 triggered moderate upregulation of VRT-A2 results in significantly increased grain weight without the yield penalty. Our study thus provides a feasible strategy for overcoming the tradeoffs of pleotropic genes by editing their upstream transcriptional regulators.

The E3 ligase OsHel2 impedes readthrough of stalled mRNAs to regulate male fertility in thermosensitive genic male sterile rice

Heterosis is extensively used in the 2-line hybrid breeding system. Photosensitive/thermosensitive genic male sterile (P/TGMS) lines are key components of 2-line hybrid rice, and TGMS lines containing tms5 have significantly advanced 2-line hybrid rice breeding. We cloned the TMS5 gene and found that TMS5 is a tRNA cyclic phosphatase that can remove 2',3'-cyclic phosphate (cP) from cP-ΔCCA-tRNAs for efficient repair to ensure maintenance of mature tRNA levels. tms5 mutation causes increased levels of cP-ΔCCA-tRNAs and reduced levels of mature tRNAs, leading to male sterility at restrictive temperatures. However, the regulatory network of tms5-mediated TGMS remains to be clarified. Here, we demonstrate that the E3 ligase OsHel2 cooperates with TMS5 to regulate TGMS at restrictive temperatures. Consistently, both the accumulation of cP-ΔCCA-tRNAs and the reduction in mature tRNAs in the tms5 mutant are largely recovered in the tms5 oshel2-1 mutant. A lesion in OsHel2 results in partial readthrough of the stalled sequences, thereby enabling evasion of ribosome-associated protein quality control (RQC) surveillance. Our findings reveal a mechanism by which OsHel2 impedes readthrough of stalled mRNA sequences to regulate male fertility in TGMS rice, providing a paradigm for investigating how disorders in components of the RQC pathway impair cellular functions and lead to diseases or defects in other organisms.

Advances in plant male sterility for hybrid seed production: an overview of conditional nuclear male sterile lines and biotechnology-based male sterile systems

Male sterility forms the foundation of hybrid seed production technology in field crops. A variety of genetically controlled male sterility/fertility systems starting with cytoplasmic male sterility (CMS), genic male sterility (GMS) including conditional male sterility and transgenic-based male sterility have been developed and deployed for heterosis breeding over the past century. Here we review environment-sensitive genic male sterility (EGMS) and biotechnology-based male sterility systems and describe the underlying molecular mechanisms. Advances in crop genomics and discovery of a large number of nuclear genes governing anther/pollen development, which are shared across species, are helping design diverse types of male sterile lines suitable for different crop species and situations. In particular, gene editing offers quick and easy route to develop novel male sterility systems for hybrid seed production. We discuss the advantages and challenges of biotechnology-based male sterility systems and present alternative strategies to address concerns of transgenics. Finally, we propose development of functional male sterility systems based on pollen competition as the future area that holds great promise for heterosis breeding.

The Residual Activity of Fatty Acyl-CoA Reductase Underlies Thermo-Sensitive Genic Male Sterility in Rice

Photoperiod/thermo-sensitive genic male sterility (P/TGMS) is critical for rice two-line hybrid system. Previous studies showed that slow development of pollen is a general mechanism for sterility-to-fertility conversion of TGMS in Arabidopsis. However, whether this mechanism still exists in rice is unknown. Here, we identified a novel rice TGMS line, ostms16, which exhibits abnormal pollen exine under high temperature and fertility restoration under low temperature. In mutant, a single base mutation of OsTMS16, a fatty acyl-CoA reductase (FAR), reduced its enzyme activity, leading to defective pollen wall. Under high temperature, the mOsTMS16M549I couldn't provide sufficient protection for the microspores. Under low temperature, the enzyme activity of mOsTMS16M549I is closer to that of OsTMS16, so that the imperfect exine could still protect microspore development. These results indicated whether the residual enzyme activity in mutant could meet the requirement in different temperature is a determinant factor for fertility conversion of P/TGMS lines. Additionally, we previously found that res2, the mutant of a polygalacturonase for tetrad pectin wall degradation, restored multiple TGMS lines in Arabidopsis. In this study, we proved that the osres2 in rice restored the fertility of ostms16, indicating the slow development is also suitable for the fertility restoration in rice.

Molecular and cellular mechanisms of photoperiod- and thermo-sensitive genic male sterility in plants

Photoperiod- and thermo-sensitive genic male sterile (P/TGMS) lines display male sterility under high-temperature/long-day light conditions and male fertility under low-temperature/short-day light conditions. P/TGMS lines are the fundamental basis for the two-line hybrid breeding, which has notably increased the yield potential and grain quality of rice cultivars. In this review, we focus on the research progress on photoperiod- and thermo-sensitive genic male sterility in plants. The essence of P/TGMS line is their ability to produce viable pollen under varying conditions. We overview the processes involved in anther and pollen development, as well as the molecular, cellular, and genetic mechanisms underlying P/TGMS in Arabidopsis, rice, and other crops. Slow development has been identified as a common mechanism of P/TGMS fertility restoration in both Arabidopsis and rice, while reactive oxygen species homeostasis has been implicated in rice P/TGMS. Furthermore, we discuss the prospective applications of P/TGMS and potential solutions to the challenges in this field. This review deepens the understanding of the mechanisms underlying P/TGMS and its utilization in two-line hybrid breeding across diverse crops.

Plastid-localized ZmENR1/ZmHAD1 complex ensures maize pollen and anther development through regulating lipid and ROS metabolism

Lipid metabolism is critical for male reproduction in plants. Many lipid-metabolic genic male-sterility (GMS) genes function in the anther tapetal endoplasmic reticulum, while little is known about GMS genes involved in de novo fatty acid biosynthesis in the anther tapetal plastid. In this study, we identify a maize male-sterile mutant, enr1, with early tapetal degradation, defective anther cuticle, and pollen exine. Using genetic mapping, we clone a key GMS gene, ZmENR1, which encodes a plastid-localized enoyl-acyl carrier protein (ACP) reductase. ZmENR1 interacts with β-hydroxyacyl-ACP dehydratase (ZmHAD1) to enhance the efficiency of de novo fatty acid biosynthesis. Furthermore, the ZmENR1/ZmHAD1 complex is regulated by a Maize Male Sterility 1 (ZmMS1)-mediated feedback repression loop to ensure anther cuticle and pollen exine formation by affecting the expression of cutin/wax- and sporopollenin-related genes. Intriguingly, homologous genes of ENR1 from rice and Arabidopsis also regulate male fertility, suggesting that the ENR1-mediated pathway likely represents a conserved regulatory mechanism underlying male reproduction in flowering plants.

Identification of the new allele ptc1-2 and analysis of the regulatory role of PTC1 gene in rice anther development

Anther development involves a series of important biological events that are precisely regulated by many genes. Although several important genes involved in rice anther development have been identified, the regulatory network involved in tapetal development and pollen wall formation is still largely unclear. PERSISTENT TAPETAL CELL 1 (PTC1) encodes a PHD-Finger protein, which plays a critical role in the regulation of tapetal cell death and pollen development in rice. Here, we report the isolation and characterization of a new allele ptc1-2 with 2-base deletion in the third exon, causing the absent of the PHD domain due to the sequence change. Cytological analysis revealed delayed tapetal PCD, defective pollen exine formation and abnormal ubisch bodies development. Transcriptome analysis revealed that genes related to pollen wall formation (secondary metabolism, phenylalanine synthesis, and cutin and wax biosynthesis pathways), cell death (cysteine and methionine metabolism and DNA repair pathways), and carbohydrate synthesis (starch and sucrose metabolism pathways) were significantly altered in ptc1-2 mutant. A total of 13 reported anther development genes exhibited significant expression changes in the ptc1-2 mutant. Yeast two-hybrid and BiFC analyses showed that PTC1 could interact with API5, an inhibitor of apoptosis, and the citrin-binding enzyme EDT1. This work is helpful in deepening the understanding of the regulatory network of male reproductive development in rice.

Impaired 2',3'-cyclic phosphate tRNA repair causes thermo-sensitive genic male sterility in rice

Hybrid rice, widely planted in Asia, is pathogen resistant and has superior yields, making it a major contributor to global food security. The two-line hybrid rice system, which utilizes mutants exhibiting photo-/thermo-sensitive genic male sterility (P/TGMS), is the leading hybrid rice breeding technology. Mutations in THERMO-SENSITIVE GENIC MALE STERILE 5 (TMS5) accounts for over 95% of current TGMS lines. We previously found that tms5 carries a mutation in ribonuclease ZS1. Despite its importance for breeding robust rice lines, the mechanism underlying tms5-mediated TGMS remains elusive. Here, we demonstrate that TMS5 is a tRNA 2',3'-cyclic phosphatase. The tms5 mutation leads to accumulation of 2',3'-cyclic phosphate (cP)-ΔCCA-tRNAs (tRNAs without 3' CCA ended with cP), which is exacerbated by high temperatures, and reduction in the abundance of mature tRNAs, particularly alanine tRNAs (tRNA-Alas). Overexpression of tRNA-Alas in the tms5 mutant restores male fertility to 70%. Remarkably, male fertility of tms5 mutant is completely restored at high temperatures by knocking out OsVms1 which encodes the enzyme for cP-ΔCCA-tRNA generation. Our study reveals the mechanism underlying tms5-mediated TGMS in rice and provides mechanistic insight into the further improvement of TGMS in hybrid crop development.

Near-infrared remote triggering of bio-enzyme activation to control intestinal colonization by orally administered microorganisms

Oral biotherapeutics hold significant promise, but their lack of controllability and targeting poses a major challenge, particularly for intestinal bacterial biotherapeutics. In response, we have developed a nanoencapsulation approach that responds to the release of enzyme activity in the organism and activates the enzyme in situ, allowing for controlled colonization of microbes in the gut. The nano-coating comprises a two-layer structure: an inner layer of polydopamine with photothermal and adhesive properties, and an outer layer of gelatin-sodium carboxymethylcellulose, which is hydrolyzed by cellulases in the gut following photothermal interaction with dopamine. We have successfully achieved controlled colonization of a wide range of microorganisms. Furthermore, in a diabetes model, this approach has had a profound impact on regulating glucagon-like peptide-1 (GLP-1) production, β-cell physiology, and promoting insulin secretion. This nanocoating is achieved by in situ activation of cellulase without the need for genetic or targeted molecular modification, representing a new paradigm and alternative strategy for microbial therapy. It not only enables precise and controlled colonization of probiotics but also demonstrates great potential for broader application in the field of oral biotherapy. STATEMENT OF SIGNIFICANCE: We have developed a nano-encapsulation method that triggers enzyme activity in response to enzymatic activity, resulting in the controlled release and adhesion of a wide range of microorganisms in the gut. The nano coating comprises two layers: an inner layer of polydopamine with photothermal and adhesion properties, and an outer layer of a gelatin-sodium carboxymethylcellulose polymer, which can be hydrolyzed by cellulases in the intestine. Additionally, this method allows for the preparation of various microbial coatings. This approach holds significant promise for regulating GLP-1 production, the physiological function of pancreatic β-cells, and promoting insulin secretion in diabetes models.

GLUTAMYL-tRNA SYNTHETASE 1 deficiency confers thermosensitive male sterility in rice by affecting reactive oxygen species homeostasis

Temperature is one of the key environmental factors influencing crop fertility and yield. Understanding how plants sense and respond to temperature changes is, therefore, crucial for improving agricultural production. In this study, we characterized a temperature-sensitive male sterile mutant in rice (Oryza sativa), glutamyl-tRNA synthetase 1-2 (ers1-2), that shows reduced fertility at high temperatures and restored fertility at low temperatures. Mutation of ERS1 resulted in severely delayed pollen development and meiotic progression at high temperatures, eventually leading to male sterility. Moreover, meiosis-specific events, including synapsis and crossover formation, were also delayed in ers1-2 compared with the wild type. However, these defects were all mitigated by growing ers1-2 at low temperatures. Transcriptome analysis and measurement of ascorbate, glutathione, and hydrogen peroxide (H2O2) contents revealed that the delayed meiotic progression and male sterility in ers1-2 were strongly associated with changes in reactive oxygen species (ROS) homeostasis. At high temperatures, ers1-2 exhibited decreased accumulation of ROS scavengers and overaccumulation of ROS. In contrast, at low temperatures, the antioxidant system of ROS was more active, and ROS contents were lower. These data suggest that ROS homeostasis in ers1-2 is disrupted at high temperatures but restored at low temperatures. We speculate that ERS1 dysfunction leads to changes in ROS homeostasis under different conditions, resulting in delayed or rescued meiotic progression and thermosensitive male fertility. ers1-2 may hold great potential as a thermosensitive material for crop heterosis breeding.

Molecular mechanisms underlying the negative effects of transient heatwaves on crop fertility

Transient heatwaves occurring more frequently as the climate warms, yet their impacts on crop yield are severely underestimated and even overlooked. Heatwaves lasting only a few days or even hours during sensitive stages, such as microgametogenesis and flowering, can significantly reduce crop yield by disrupting plant reproduction. Recent advances in multi-omics and GWAS analysis have shed light on the specific organs (e.g., pollen, lodicule, style), key metabolic pathways (sugar and reactive oxygen species metabolism, Ca2+ homeostasis), and essential genes that are involved in crop responses to transient heatwaves during sensitive stages. This review therefore places particular emphasis on heat-sensitive stages, with pollen development, floret opening, pollination, and fertilization as the central narrative thread. The multifaceted effects of transient heatwaves and their molecular basis are systematically reviewed, with a focus on key structures such as the lodicule and tapetum. A number of heat-tolerance genes associated with these processes have been identified in major crops like maize and rice. The mechanisms and key heat-tolerance genes shared among different stages may facilitate the more precise improvement of heat-tolerant crops.

Structural variations of a new fertility restorer gene, Rf20, underlie the restoration of wild abortive-type cytoplasmic male sterility in rice

The discovery of a wild abortive-type (WA) cytoplasmic male sterile (CMS) line and breeding its restorer line have led to the commercialization of three-line hybrid rice, contributing considerably to global food security. However, the molecular mechanisms underlying fertility abortion and the restoration of CMS-WA lines remain largely elusive. In this study, we cloned a restorer gene, Rf20, following a genome-wide association study analysis of the core parent lines of three-line hybrid rice. We found that Rf20 was present in all core parental lines, but different haplotypes and structural variants of its gene resulted in differences in Rf20 expression levels between sterile and restored lines. Rf20 could restore pollen fertility in the CMS-WA line and was found to be responsible for fertility restoration in some CMS lines under high temperatures. In addition, we found that Rf20 encodes a pentatricopeptide repeat protein that competes with WA352 for binding with COX11. This interaction enhances COX11's function as a scavenger of reactive oxygen species, which in turn restores pollen fertility. Collectively, our study suggests a new action mode for pentatricopeptide repeat proteins in the fertility restoration of CMS lines, providing an essential theoretical basis for breeding robust restorer lines and for overcoming high temperature-induced fertility recovery of some CMS lines.

Temperature and light reverse the fertility of rice P/TGMS line ostms19 via reactive oxygen species homeostasis

P/TGMS (Photo/thermo-sensitive genic male sterile) lines are crucial resources for two-line hybrid rice breeding. Previous studies revealed that slow development is a general mechanism for sterility-fertility conversion of P/TGMS in Arabidopsis. However, the difference in P/TGMS genes between rice and Arabidopsis suggests the presence of a distinct P/TGMS mechanism in rice. In this study, we isolated a novel P/TGMS line, ostms19, which shows sterility under high-temperature conditions and fertility under low-temperature conditions. OsTMS19 encodes a novel pentatricopeptide repeat (PPR) protein essential for pollen formation, in which a point mutation GTA(Val) to GCA(Ala) leads to ostms19 P/TGMS phenotype. It is highly expressed in the tapetum and localized to mitochondria. Under high temperature or long-day photoperiod conditions, excessive ROS accumulation in ostms19 anthers during pollen mitosis disrupts gene expression and intine formation, causing male sterility. Conversely, under low temperature or short-day photoperiod conditions, ROS can be effectively scavenged in anthers, resulting in fertility restoration. This indicates that ROS homeostasis is critical for fertility conversion. This relationship between ROS homeostasis and fertility conversion has also been observed in other tested rice P/TGMS lines. Therefore, we propose that ROS homeostasis is a general mechanism for the sterility-fertility conversion of rice P/TGMS lines.

Modulation of histone acetylation enables fully mechanized hybrid rice breeding

Hybrid rice has achieved high grain yield and greatly contributes to food security, but the manual-labour-intensive hybrid seed production process limits fully mechanized hybrid rice breeding. For next-generation hybrid seed production, the use of small-grain male sterile lines to mechanically separate small hybrid seeds from mixed harvest is promising. However, it is difficult to find ideal grain-size genes for breeding ideal small-grain male sterile lines without penalties in the number of hybrid seeds and hybrid rice yield. Here we report that the use of small-grain alleles of the ideal grain-size gene GSE3 in male sterile lines enables fully mechanized hybrid seed production and dramatically increases hybrid seed number in three-line and two-line hybrid rice systems. The GSE3 gene encodes a histone acetyltransferase that binds histones and influences histone acetylation levels. GSE3 is recruited by the transcription factor GS2 to the promoters of their co-regulated grain-size genes and influences the histone acetylation status of their co-regulated genes. Field trials demonstrate that genome editing of GSE3 can be used to immediately improve current elite male sterile lines of hybrid rice for fully mechanized hybrid rice breeding, providing a new perspective for mechanized hybrid breeding in other crops.

Editing of ORF138 restores fertility of Ogura cytoplasmic male sterile broccoli via mitoTALENs

Cytoplasmic male sterility (CMS), encoded by the mitochondrial open reading frames (ORFs), has long been used to economically produce crop hybrids. However, the utilization of CMS also hinders the exploitation of sterility and fertility variation in the absence of a restorer line, which in turn narrows the genetic background and reduces biodiversity. Here, we used a mitochondrial targeted transcription activator-like effector nuclease (mitoTALENs) to knock out ORF138 from the Ogura CMS broccoli hybrid. The knockout was confirmed by the amplification and re-sequencing read mapping to the mitochondrial genome. As a result, knockout of ORF138 restored the fertility of the CMS hybrid, and simultaneously manifested a cold-sensitive male sterility. ORF138 depletion is stably inherited to the next generation, allowing for direct use in the breeding process. In addition, we proposed a highly reliable and cost-effective toolkit to accelerate the life cycle of fertile lines from CMS-derived broccoli hybrids. By applying the k-mean clustering and interaction network analysis, we identified the central gene networks involved in the fertility restoration and cold-sensitive male sterility. Our study enables mitochondrial genome editing via mitoTALENs in Brassicaceae vegetable crops and provides evidence that the sex production machinery and its temperature-responsive ability are regulated by the mitochondria.

Key candidate genes for male sterility in peppers unveiled via transcriptomic and proteomic analyses

This study aimed to enhance the use of male sterility in pepper to select superior hybrid generations. Transcriptomic and proteomic analyses of fertile line 1933A and nucleic male sterility line 1933B of Capsicum annuum L. were performed to identify male sterility-related proteins and genes. The phylogenetic tree, physical and chemical characteristics, gene structure characteristics, collinearity and expression characteristics of candidate genes were analyzed. The study identified 2,357 differentially expressed genes, of which 1,145 and 229 were enriched in the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases, respectively. A total of 7,628 quantifiable proteins were identified and 29 important proteins and genes were identified. It is worth noting that the existence of CaPRX genes has been found in both proteomics and transcriptomics, and 3 CaPRX genes have been identified through association analysis. A total of 66 CaPRX genes have been identified at the genome level, which are divided into 13 subfamilies, all containing typical CaPRX gene conformal domains. It is unevenly distributed across 12 chromosomes (including the virtual chromosome Chr00). Salt stress and co-expression analysis show that male sterility genes are expressed to varying degrees, and multiple transcription factors are co-expressed with CaPRXs, suggesting that they are involved in the induction of pepper salt stress. The study findings provide a theoretical foundation for genetic breeding by identifying genes, metabolic pathways, and molecular mechanisms involved in male sterility in pepper.

MADS8 is indispensable for female reproductive development at high ambient temperatures in cereal crops

Temperature is a major factor that regulates plant growth and phenotypic diversity. To ensure reproductive success at a range of temperatures, plants must maintain developmental stability of their sexual organs when exposed to temperature fluctuations. However, the mechanisms integrating plant floral organ development and temperature responses are largely unknown. Here, we generated barley and rice loss-of-function mutants in the SEPALLATA-like MADS-box gene MADS8. The mutants in both species form multiple carpels that lack ovules at high ambient temperatures. Tissue-specific markers revealed that HvMADS8 is required to maintain floral meristem determinacy and ovule initiation at high temperatures, and transcriptome analyses confirmed that temperature-dependent differentially expressed genes in Hvmads8 mutants predominantly associate with floral organ and meristem regulation. HvMADS8 temperature-responsive activity relies on increased binding to promoters of downstream targets, as revealed by a cleavage under targets and tagmentation (CUT&Tag) analysis. We also demonstrate that HvMADS8 directly binds to 2 orthologs of D-class floral homeotic genes to activate their expression. Overall, our findings revealed a new, conserved role for MADS8 in maintaining pistil number and ovule initiation in cereal crops, extending the known function of plant MADS-box proteins in floral organ regulation.

A natural mutation in the promoter of Ms-cd1 causes dominant male sterility in Brassica oleracea

Male sterility has been used for crop hybrid breeding for a long time. It has contributed greatly to crop yield increase. However, the genetic basis of male sterility has not been fully elucidated. Here, we report map-based cloning of the cabbage (Brassica oleracea) dominant male-sterile gene Ms-cd1 and reveal that it encodes a PHD-finger motif transcription factor. A natural allele Ms-cd1PΔ-597, resulting from a 1-bp deletion in the promoter, confers dominant genic male sterility (DGMS), whereas loss-of-function ms-cd1 mutant shows recessive male sterility. We also show that the ethylene response factor BoERF1L represses the expression of Ms-cd1 by directly binding to its promoter; however, the 1-bp deletion in Ms-cd1PΔ-597 affects the binding. Furthermore, ectopic expression of Ms-cd1PΔ-597 confers DGMS in both dicotyledonous and monocotyledonous plant species. We thus propose that the DGMS system could be useful for breeding hybrids of multiple crop species.

Structural and molecular basis of pollen germination

Pollen germination is a prerequisite for double fertilization of flowering plants. A comprehensive understanding of the structural and molecular basis of pollen germination holds great potential for crop yield improvement. The pollen aperture serves as the foundation for most plant pollen germination and pollen aperture formation involves the establishment of cellular polarity, the formation of distinct membrane domains, and the precise deposition of extracellular substances. Successful pollen germination requires precise material exchange and signal transduction between the pollen grain and the stigma. Recent cytological and mutant analysis of pollen germination process in Arabidopsis and rice has expanded our understanding of this biological process. However, the overall changes in germination site structure and energy-related metabolites during pollen germination remain to be further explored. This review summarizes and compares the recent advances in the processes of pollen aperture formation, pollen adhesion, hydration, and germination between eudicot Arabidopsis and monocot rice, and provides insights into the structural basis and molecular mechanisms underlying pollen germination process.

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.

Low temperature compensates for defective tapetum initiation to restore the fertility of the novel TGMS line ostms15

In rice breeding, thermosensitive genic male sterility (TGMS) lines based on the tms5 locus have been extensively employed. Here, we reported a novel rice TGMS line ostms15 (Oryza sativa ssp. japonica ZH11) which show male sterility under high temperature and fertility under low temperature. Field evaluation from 2018 to 2021 revealed that its sterility under high temperature is more stable than that of tms5 (ZH11), even with occasional low temperature periods, indicating its considerable value for rice breeding. OsTMS15 encodes an LRR-RLK protein MULTIPLE SPOROCYTE1 (MSP1) which was reported to interact with its ligand to initiate tapetum development for pollen formation. In ostms15, a point mutation from GTA (Val) to GAA (Glu) in its TIR motif of the LRR region led to the TGMS phenotype. Cellular observation and gene expression analysis showed that the tapetum is still present in ostms15, while its function was substantially impaired under high temperature. However, its tapetum function was restored under low temperature. The interaction between mOsTMS15 and its ligand was reduced while this interaction was partially restored under low temperature. Slow development was reported to be a general mechanism of P/TGMS fertility restoration. We propose that the recovered protein interaction together with slow development under low temperature compensates for the defective tapetum initiation, which further restores ostms15 fertility. We used base editing to create a number of TGMS lines with different base substitutions based on the OsTMS15 locus. This work may also facilitate the mechanistic investigation and breeding of other crops.

High-temperature stress in crops: male sterility, yield loss and potential remedy approaches

Global food security is one of the utmost essential challenges in the 21st century in providing enough food for the growing population while coping with the already stressed environment. High temperature (HT) is one of the main factors affecting plant growth, development and reproduction and causes male sterility in plants. In male reproductive tissues, metabolic changes induced by HT involve carbohydrates, lipids, hormones, epigenetics and reactive oxygen species, leading to male sterility and ultimately reducing yield. Understanding the mechanism and genes involved in these pathways during the HT stress response will provide a new path to improve crops by using molecular breeding and biotechnological approaches. Moreover, this review provides insight into male sterility and integrates this with suggested strategies to enhance crop tolerance under HT stress conditions at the reproductive stage.

MOTHER-OF-FT-AND-TFL1 regulates the seed oil and protein content in soybean

Soybean is a major crop that produces valuable seed oil and protein for global consumption. Seed oil and protein are regulated by complex quantitative trait loci (QTLs) and have undergone intensive selections during the domestication of soybean. It is essential to identify the major genetic components and understand their mechanism behind seed oil and protein in soybean. We report that MOTHER-OF-FT-AND-TFL1 (GmMFT) is the gene of a classical QTL that has been reported to regulate seed oil and protein content in many studies. Mutation of MFT decreased seeds oil content and weight in both Arabidopsis and soybean, whereas increased expression of GmMFT enhanced seeds oil content and weight. Haplotype analysis showed that GmMFT has undergone selection, which resulted in the extended haplotype homozygosity in the cultivated soybean and the enriching of the oil-favorable allele in modern soybean cultivars. This work unraveled the GmMFT-mediated mechanism regulating seed oil and protein content and seed weight, and revealed a previously unknown function of MFT that provides new insights into targeted soybean improvement and breeding.

A Systematic Investigation of Lipid Transfer Proteins Involved in Male Fertility and Other Biological Processes in Maize

Plant lipid transfer proteins (LTPs) play essential roles in various biological processes, including anther and pollen development, vegetative organ development, seed development and germination, and stress response, but the research progress varies greatly among Arabidopsis, rice and maize. Here, we presented a preliminary introduction and characterization of the whole 65 LTP genes in maize, and performed a phylogenetic tree and gene ontology analysis of the LTP family members in maize. We compared the research progresses of the reported LTP genes involved in male fertility and other biological processes in Arabidopsis and rice, and thus provided some implications for their maize orthologs, which will provide useful clues for the investigation of LTP transporters in maize. We predicted the functions of LTP genes based on bioinformatic analyses of their spatiotemporal expression patterns by using RNA-seq and qRT-PCR assays. Finally, we discussed the advances and challenges in substrate identification of plant LTPs, and presented the future research directions of LTPs in plants. This study provides a basic framework for functional research and the potential application of LTPs in multiple plants, especially for male sterility research and application in maize.

Comparative transcriptome analysis provides insight into the important pathways and key genes related to the pollen abortion in the thermo-sensitive genic male sterile line 373S in Brassica napus L

The thermo-sensitive genic male sterility (TGMS) system plays a key role in the production of two-line hybrids in rapeseed (Brassica napus). To uncover key cellular events and genetic regulation associated with TGMS, a combined study using cytological methods and RNA-sequencing analysis was conducted for the rapeseed TGMS line 373S. Cytological studies showed that microspore cytoplasm of 373S plants was condensed, the microspore nucleus was degraded at an early stage, the exine was irregular, and the tapetum developed abnormally, eventually leading to male sterility. RNA-sequencing analysis identified 430 differentially expressed genes (298 upregulated and 132 downregulated) between the fertile and sterile samples. Gene ontology analysis demonstrated that the most highly represented biological processes included sporopollenin biosynthetic process, pollen exine formation, and extracellular matrix assembly. Kyoto encyclopedia of genes and genomes analysis indicated that the enriched pathways included amino acid metabolism, carbohydrate metabolism, and lipid metabolism. Moreover, 26 transcript factors were identified, which may be associated with abnormal tapetum degeneration and exine formation. Subsequently, 19 key genes were selected, which are considered to regulate pollen development and even participate in pollen exine formation. Our results will provide important insight into the molecular mechanisms underlying TGMS in rapeseed.