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

Brems1 mutation induced tapetum deficiency leading to male sterility in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

KEY MESSAGE

The mutation in Brems1 resulting in male sterility in Chinese cabbage were validated through two allelic mutations. Male sterile lines are ideal for hybrid seed production in Chinese cabbage. Herein, the complete male sterile mutants M5026 and M5073 were obtained through ethyl methanesulfonate (EMS) mutagenesis in the Chinese cabbage double haploid line 'FT'. Cytological observations revealed that M5026 exhibited an absence of the tapetum, an overabundance of microsporocytes, and abnormal exine formation in pollen. The male sterility phenotype of M5026 was controlled by a single recessive nuclear gene. Using mutmap sequencing and kompetitive allele-specific PCR (KASP) identification and gene cloning, two distinct SNPs in BraA10g029920.3.5C, encoding EMS1 (excess microsporocytes 1), were identified to be associated with the male sterility of M5026 and M5073. The gene was named as Brems1. M5026 and M5073 were determined to be allelic variants. Both BrEMS1 and Brems1 were subcellularly localized at the cell membrane. Brems1 exhibited the highest expression level in buds, while no expression was detected in roots. Transcriptomic analysis revealed that Brems1 mutations reduced the expression levels of genes associated with the tapetum, pollen tube, and LRR-RLK family. These results suggested that Brems1 played a critical role in pollen development and contributes to elucidating the molecular mechanisms underlying tapetum development and male sterility in Chinese cabbage.

Transcriptome and WGCNA reveals the potential genetic basis of photoperiod-sensitive male sterility in soybean

BACKGROUND

Soybean (Glycine max (L.) Merr.) is a crucial crop due to its high plant protein and oil content. Previous studies have shown that soybeans exhibit significant heterosis in terms of yield and protein content However, the practical application of soybean heterosis remains difficult, as the molecular mechanisms underlying photoperiod-sensitive genic male sterile (PGMS) is still unclear.

RESULTS

This study characterized the PGMS line 88-428BY, which is sterile under short-day (SD) conditions and fertile under long-day (LD) conditions. To elucidate the genetic basis for this trait, we collected anthers, from 88-428BY under SD and LD conditions at three developmental stages, resulting in the identification of differentially expressed genes (DEGs) (2333, 2727 and 7282 DEGs, respectively) using Illumina transcriptome analysis. Using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses, we fund that among the DEGs, enriched genes were associated with photoperiod stress, light stimulus, oxidation-reduction processes, multicellular organism development and protein phosphorylation. Additionally, weighted correlation network analysis identified four modules (blue, brown, red, and yellow) that were significantly correlated with PGMS, revealing co-expressed hub genes with potential regulatory roles. Functional annotation of 224 DEGs with|KME| >0.9 across the four modules in seven databases highlighted their involvement in light stimulus, oxidation-reduction processes, multicellular organism development, and protein phosphorylation, suggesting their importance in soybean PGMS. By integrating fertility-related genes previously identified by other studies with the DEGs from our analysis, we identified eight candidate genes associated with the photosensitive sterility in soybeans.

CONCLUSIONS

This study enhances the understanding of PGMS in soybean and establishes the genetic basis for a two-line hybrid seed production system in soybean.

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.

Mutations in a Leucine-Rich Repeat Receptor-Like Kinase gene result in male sterility and reduction in the number and size of fruit warts in cucumber (Cucumis sativus L.)

KEY MESSAGE

Mutations in the CsEMS1 gene result in male sterility and reduced wart number and density. Male sterility and fruit wart formation are two significant agronomic characteristics in cucumber (Cucumis sativus), yet knowledge of our underlying genetics is limited. In this study, we identified an EMS-induced male sterility and few small warts mutant (msfsw). Histological observations revealed defects the absence of tapetum, meiotic aberration and impaired microspore formation in the anthers of the mutant. The mutant also exhibits a reduction in both the size and number of fruit spines and fruit tubercules. Genetic analysis revealed that a single recessive gene is responsible for the mutant phenotypes. BSA-Seq and fine genetic mapping mapped the msfsw locus to a 63.7 kb region with four predicted genes. Multiple lines of evidence support CsEMS1(CsaV3_3G016940) as the candidate for the mutant allele which encodes an LRR receptor-like kinase, and a non-synonymous SNP inside the exon of CsEMS1 is the causal polymorphisms for the mutant phenotypes. This function of CsEMS1 in determination of pollen fertility was confirmed with generation and characterization of multiple knockout mutations with CRISPR/Cas9 based gene editing. In the wild-type (WT) plants, CsEMS1 was highly expressed in male flowers. In the mutant, the expression level of CsEMS1, several tapetum identity-related genes, and trichome-related genes were all significantly reduced as compared with the wild-type. Protein-protein interaction assays revealed physical interactions between CsEMS1 and CsTPD1. Quantitation of endogenous phytohormones revealed a reduction in the ethylene precursor ACC in CsEMS1 knockout lines. This work identified an important role of CsEMS1 in anther and pollen development as well as fruit spine/wart development in cucumber.

How Rice Responds to Temperature Changes and Defeats Heat Stress

With the intensification of the greenhouse effect, a series of natural phenomena, such as global warming, are gradually recognized; when the ambient temperature increases to the extent that it causes heat stress in plants, agricultural production will inevitably be affected. Therefore, several issues associated with heat stress in crops urgently need to be solved. Rice is one of the momentous food crops for humans, widely planted in tropical and subtropical monsoon regions. It is prone to high temperature stress in summer, leading to a decrease in yield and quality. Understanding how rice can tolerate heat stress through genetic effects is particularly vital. This article reviews how rice respond to rising temperature by integrating the molecular regulatory pathways and introduce its physiological mechanisms of tolerance to heat stress from the perspective of molecular biology. In addition, genome selection and genetic engineering for rice heat tolerance were emphasized to provide a theoretical basis for the sustainability and stability of crop yield-quality structures under high temperatures from the point of view of molecular breeding.

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.

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.

A point mutation in the meiotic crossover formation gene HEI10/TFS2 leads to thermosensitive genic sterility in rice

Thermosensitive genic female sterility (TGFS) is a promising property to be utilized for hybrid breeding. Here, we identified a rice TGFS line, tfs2, through an ethyl methyl sulfone (EMS) mutagenesis strategy. This line showed sterility under high temperature and became fertile under low temperature. Few seeds were produced when the tfs2 stigma was pollinated, indicating that tfs2 is female sterile. Gene cloning and genetic complementation showed that a point mutation from leucine to phenylalanine in HEI10 (HEI10tfs2), a crossover formation protein, caused the TGFS trait of tfs2. Under high temperature, abnormal univalents were formed, and the chromosomes were unequally segregated during meiosis, similar to the reported meiotic defects in oshei10. Under low temperature, the number of univalents was largely reduced, and the chromosomes segregated equally, suggesting that crossover formation was restored in tfs2. Yeast two-hybrid assays showed that HEI10 interacted with two putative protein degradation-related proteins, RPT4 and SRFP1. Through transient expression in tobacco leaves, HEI10 were found to spontaneously aggregate into dot-like foci in the nucleus under high temperature, but HEI10tfs2 failed to aggregate. In contrast, low temperature promoted HEI10tfs2 aggregation. This result suggests that protein aggregation at the crossover position contributes to the fertility restoration of tfs2 under low temperature. In addition, RPT4 and SRFP1 also aggregated into dot-like foci, and these aggregations depend on the presence of HEI10. These findings reveal a novel mechanism of fertility restoration and facilitate further understanding of HEI10 in meiotic crossover formation.