ROS accumulation-induced tapetal PCD timing changes leads to microspore abortion in cotton CMS lines

In vitro activity of seven antifungal agents against Fusarium oxysporum and expression of related regulatory genes

Fusarium oxysporum (F. oxysporum) is one of the main pathogenic fungus causing maize ear rot. In this study, the aims were to screen highly effective pesticides for F. oxysporum, reduce peasants' misunderstandings about pesticide application, improve disease control levels, and enhance economic efficiency. The toxicity of seven fungicides (carbendazim, pyraclostrobin, epoxiconazole, tricyclazole, azoxystrobin, difenoconazole, quintozene) on F. oxysporum were determined by the mycelium growth rate and the spore germination method, and single and compound fungicides with effective inhibitory effects on mycelial growth were screened. The RT-qPCR method was used to detect the expression levels of chitin synthetase V (ChsV), folate uptake block T (FUBT), superoxide dismutase (SOD), and peroxidase dismutase (POD) genes in pathogenic bacteria treated with the selected agents and combination of fungicides. The results showed that all seven fungicides had inhibitory effects on mycelial growth hyphae and spore germination of F. oxysporum. Epoxiconazole had the strongest inhibitory effect on mycelium growth and spore germination of F. oxysporum, with effective concentrations (EC50) of 0.047 and 0.088 μg/mL, respectively. The combination of pyraclostrobin and difenoconazole (P&D, combined at a mass ratio of 7:3) had the best inhibitory effect, with an EC50 of 0.094 μg/mL and an SR of 2.650. Epoxiconazole and the combination P&D could inhibit mycelial growth and spore germination by down-regulating ChsV, FUBT, and POD, causing oxidative stress in F. oxysporum, and reducing the occurrence of maize ear rot.

Differences in homologous and heterologous nucleocytoplasmic interactions of cytoplasmic male sterility lines in Gossypium barbadense

The utilization of crop hybrids plays an important role in crop breeding and production, and the innovation of the male sterile germplasm is the basis for this utilization. Cotton has a very clear hybrid advantage, and the hybrid advantage in yield and quality has been widely utilized in cotton breeding. However, the exploitation of heterosis in cotton is currently dominated by cytoplasmic male sterility (CMS) lines. These CMS lines are found only in Harknessi cotton. They have a single cytoplasmic origin. Additionally, they exhibit a significant negative effect of cytoplasmic-nuclear interactions. To minimize this effect, it is necessary to select and breed CMS lines. In these CMS lines, both the cytoplasm and nucleus should originate from the same variety. However, no homologous cytoplasmic-nuclear CMS germplasm has been created, and its mechanism of occurrence has not been determined. In this study, two homologous cytoplasmic-nuclear CMS lines and two heterologous cytoplasmic-nuclear CMS lines were utilized, and the heterologous cytoplasmic-nuclear CMS lines were aborted at a relatively early stage. The physiological indexes related to reactive oxygen species ROS-mediated metabolic processes in the heterologous cytoplasmic-nuclear CMS lines were lower than those of the homologous cytoplasmic-nuclear CMS lines, including the enzyme activities of POD and CAT from tetrad to mature pollen grain, and the metabolite content of malondialdehyde (MDA) was inversely correlated with the enzyme activities of the heterologous cytoplasmic-nuclear CMS lines. Resequencing analysis of four cotton mitochondrial genomes (mt genomes) revealed that the heterologous cytoplasmic-nuclear CMS lines were more complex than the homologous cytoplasmic-nuclear CMS lines, and the homologous CMS lines showed a higher degree of collinearity with the maintainer lines. This indicates that heterologous cytoplasmic-nuclear interactions are more likely to lead to mtDNA structural variation. Taken together, the results showed that the cytoplasmic-nuclear homologous system was less affected by the cytoplasmic-nuclear interaction and was the best combination for the study of male sterility.

Unraveling the role of autophagy and antioxidants in anther and pistil responses to heat stress in rapeseed (Brassica napus L.)

KEY MESSAGE

Enhanced antioxidant enzymes activity, particularly superoxide dismutase and catalase, along with autophagy process in reproductive organs, can improve the resilience of rapeseed to heat stress, thereby securing crop yield in the face of global warming. Climate change and global warming have increasingly influenced yield and quality of rapeseed (Brassica napus) almost all across the world. The response of reproductive organs to high-temperature stress was studied in two rapeseed varieties, SAFI5 and DH13 with contrasting levels of heat stress tolerance. Pollen germination, viability, and seed set showed a significant reduction in the heat-sensitive variety (DH13). Superoxide quantification revealed higher accumulation in heat-sensitive variety, leading to decreased seed formation and floret fertility most probably due to declined pollen viability and stigma receptivity. Further microscopic analysis of the anther and pistil demonstrated a significant overlay between the damaged areas and the location of O2- accumulation. The sensitive variety showed higher O2- accumulation and a wider damage area than the tolerant one, suggesting that superoxide could incapacitate anther and pistil due to structural injury. Moreover, the activity levels and expression of superoxide dismutase and catalase antioxidant enzymes were significantly higher in the anther and pistil of the tolerant variety. Histochemical analysis also indicated markedly higher autophagosome formation in tolerant variety's anther and pistil. Consistently, the expression levels of autophagy and ubiquitin-proteasome system (UPS)-related genes including BnATG8d, BnEXO70B, BnATl1 4A, and BnNBR1, as well as ubiquitin-activating enzyme E1, were higher in both reproductive organs of the tolerant variety. Interestingly, the areas of autophagosome formation overlapped with the areas in which higher superoxide accumulation and structural changes happened, suggesting a specific role of autophagy in oxidative stress response.

Spatiotemporal regulation of anther's tapetum degeneration paved the way for a reversible male sterility system in cotton

Male sterility is an important agronomical trait in self-pollinating plants for producing cost-effective F1 hybrids to harness the heterosis. Still, large-scale development and maintenance of male sterile lines and restoring fertility in F1 hybrids pose significant challenges in plant hybrid breeding. Cotton is a self-pollinating crop and exhibits strong hybrid vigor. However, there are currently few breeding methods to achieve cost-effective production of F1 hybrid cotton. Here, we utilized novel functions of the Arabidopsis autophagy-related BECLIN1/ATG6 and a mutant of E3 ubiquitin ligase COP1 (COP1L105A) genes in developing rescuable male sterility in cotton. We have generated multiple male-sterile (MS) and restorer (RS) cotton lines expressing BECLIN1 and COP1L105A, respectively. Cytological observation showed that post-meiotic tapetal expression of BECLIN1 delays tapetum developmental programmed cell death (dPCD) by affecting reactive oxygen species (ROS) balance-this delay in dPCD results in early microspore defects and later small-sized flowers with indehiscent anthers. Furthermore, the evaluation of F1 hybrids developed by crossing MS and RS lines showed that early tapetal COP1L105A expression abolishes expression of BECLIN1 resulting in normal tapetum degeneration, pollen development, and fertility. In addition, the F1 hybrid developed with MS and RS cotton lines in transgenic glass-house and net-house conditions showed the rescued fertility comparable with control plants (WT). In terms of cotton fiber productivity, the COP1L105A-expressing transgenic cotton lines outperformed the WT. The current work effectively demonstrates the wider applicability of the new F1 cotton production system.

Effect of glutathione reductase on photosystem II characterization and reactive oxygen species metabolism in cotton cytoplasmic male sterile line Jin A

Glutathione reductase (GR) maintains the cellular redox state by reducing oxidized glutathione to glutathione (GSH), which regulates antioxidant defense. Additionally, GR plays an essential role in photosynthesis; however, the mechanism by which GR regulates photosystem II (PSII) is largely unknown. We identified six, three, and three GR genes in Gossypium hirsutum, Gossypium arboreum, and Gossypium raimondii, respectively. We found that GhGR1 and GhGR3 proteins were localized in the chloroplasts, whereas GhGR5 was localized in the cell membrane. Cytoplasmic male sterile (CMS) line Jin A was ideal to explore GR functions because accumulation of reactive oxygen species (ROS) was increased and expression of GhGR was downregulated at the key stage of microspore abortion in anthers compared to maintainer Jin B. The GR activity and relative GhGR1, GhGR3, GhGR5 gene expressions decreased significantly at the key stage of microspore abortion in Jin A-CMS compared to that in Jin B, resulting in an increase in ROS and a decrease in photochemical efficiency in PSII. GhGR1 and GhGR3 overexpression in Arabidopsis decreased ROS levels in anthers and leaves compared to the wild-type. Biochemical analysis of GhGR1 and GhGR3 silencing in Gossypium L. showed that ROS content was increased and photochemical efficiency of PSII was inhibited in leaves. Complementation experiments in tobacco and yeast indicated that GhGR1 interacted with GhPsbX, which was one of the subunits of the PSII protein complex. Taken together, these findings suggest that chloroplast GR plays an important role in PSII and ROS metabolism by interacting with PsbX in cotton plants.

Transcriptomics and metabolomics analyses reveal pollen abortion mechanism in alfalfa early stage male sterile lines

Alfalfa (Medicago sativa L.), a prominent perennial forage in the legume family, is widely cultivated across Europe and America. Given its substantial economic value for livestock, breeding efforts have focused on developing high-yield and high-quality varieties since the discovery of CMS lines. However, progress is restricted by the limitations of existing CMS lines, necessitating the development of new lines and study of the molecular mechanisms underlying pollen abortion. This study investigates early-stage anther development in cytoplasmic male sterile (CMS) alfalfa lines (MSJN1A) in relation to the isotypic maintainer line (MSJN1B). Histological analyses revealed abnormal degradation of tapetal cells post-meiosis in the CMS line. Notably, during the early mononuclear stage, the central vacuoles in the microspores were absent, leading to evident pollen abortion. These findings suggest that pollen abortion in the CMS line is associated with the delayed disintegration of the tapetum and structural anomalies in microspore vacuoles. Non-targeted metabolome sequencing revealed 401 and 405 metabolites at late tetrad and early mononuclear stages of alfalfa, respectively. Among these, 39 metabolites were consistently upregulated, whereas 85 metabolites were downregulated. Differential analysis revealed 45 and 37 unique metabolites at each respective stage. These metabolites were primarily featured in pathways related to energy, phenylpropane, sucrose and starch, and fatty acid metabolism. Integrated analysis demonstrated that differentially expressed genes and differential metabolites were co-enriched in these pathways. Additionally, quantitative real-time PCR and physiological index analysis confirmed downregulation of key genes involved in anther development, illustrating that changes in upstream gene regulation could significantly impact downstream metabolite levels, ultimately influencing pollen fertility. Pollen abortion is related to abnormal phenylpropane metabolism, fatty acid metabolism and starch and sucrose pathway, which provides reference for further research on the causes of pollen abortion of alfalfa.

Effect of Chloroplast ATP Synthase on Reactive Oxygen Species Metabolism in Cotton

Abnormal programmed cell death in the tapetum is induced by reactive oxygen species (ROS), which are the main factors leading to cytoplasmic male sterility (CMS). These abnormalities are caused by genetic interactions between nuclear and cytoplasmic genes. To explore the role of chloroplast genes in ROS metabolism, next-generation and single-molecule real-time sequencing of the chloroplast genome were performed in the cotton CMS line Jin A (Jin A-CMS). Our results showed that the chloroplast genome is 160,042 bp in length and consists of 131 genes, including 112 functional genes. An analysis of the functional annotation and sequence comparison with the Gossypium hirsutum chloroplast genome as a reference revealed that 29 genes in Jin A-CMS have single-nucleotide polymorphisms, including subunits of ATP synthase, NAD(P)H-quinone redox reductase, and photosystem complexes. Compared to the Jin B maintainer, the anthers of Jin A-CMS at the microspore abortion stage have significantly lower expression of atpB, atpE, and atpF. The relative expression of these genes is significantly higher in the three-line F1 hybrids compared to Jin A-CMS. The ROS levels in the leaves increased in response to the silencing of atpE and atpF in cotton plants. In summary, the results of our study show that the ATP synthase subunit genes atpE and atpF are closely linked with ROS metabolism. These results provide basic information for the functional analysis of ATP synthase in cotton.

Floral Developmental Morphology and Biochemical Characteristics of Male Sterile Mutants of Lagerstroemia indica

Male sterility is a common phenomenon in higher plants and often plays an important role in the selection of superior offspring. 'Xiang Yun' is a mutant of Lagerstroemia indica that does not bear fruit after flowering, and its flowering period is significantly longer than that of normal L. indica. To explore the timing and molecular mechanisms of sterility in 'Xiang Yun', this study determined the period of sterility through anatomical observation and compared the content of nutrients and the activity of antioxidative enzymes at different stages of flower development. Finally, sequence alignment and qPCR were used to analyze the differences in pollen development genes between 'Xiang Yun' and 'Hong Ye'. The results showed that the anthers of 'Xiang Yun' dispersed pollen normally, but the pollen grains could not germinate normally. Observations with scanning electron microscopy revealed that the pollen grains were uneven in size and shriveled in shape. Further observation of anther sections found that abnormal development of the microspores began at the S2 stage, with the callose wall between microspores of 'Xiang Yun' being thicker than that of 'Hong Ye'. In addition, during the flower development of 'Xiang Yun', the contents of soluble sugar, soluble protein, free proline, and triglycerides were deficient to varying degrees, and the activities of POD, SOD, and MDA were lower. Sequence alignment and qPCR showed that there were several mutations in EFD1, TPD1, and DEX1 of 'Xiang Yun' compared with 'Hong Ye', and the expression levels of these genes were abnormally elevated in the later stages of development. Our results clarified the timing and phenotype of male sterility in 'Xiang Yun'. This provides solid and valuable information for further research on the molecular mechanism of sterility in 'Xiang Yun' and the genetic breeding of crape myrtle.

HSP70 and APX1 play important roles in cotton male fertility by mediating ROS homeostasis

Male sterility is used in the production of hybrid seeds and can improve the breeding efficiency of cotton hybrids. Reactive oxygen species is closely associated with the tapetum and pollen development, but their relationship in cotton male fertility remains unclear. In this study, we comprehensively compared the cytology and proteome of the anthers from an Upland cotton (Gossypium hirsutum) material, Shida 98 (WT), and its nearly-isogenic male sterile line Shida 98A (MS). Cytology indicated delayed PCD in the tapetum and defects in microspores in MS anthers. And further studies revealed disruption of ROS homeostasis. Proteomic analysis identified proteins with differential abundance mainly being related to redox homeostasis, protein folding, and apoptotic signaling pathways. GhAPX1 interacted with GhHSP70 and played a crucial role in the development of cotton anthers. Exogenous application of HSP70 inhibitor increased H2O2 content and decreased the activity of APX1 and pollen viability. The GhAPX1 mutants generated by CRISPR/Cas9-mediated gene editing exhibited premature degradation of the tapetum, significant decrease in pollen viability, and significant increase in H2O2 content. Altogether, our results imply HSP70 and APX1 being the key players jointly regulating male fertility by mediating ROS homeostasis. These results provide insights into the proteins associated with male fertility.

Full-length RNA sequencing and single-nucleus sequencing deciphers programmed cell death and developmental trajectories in laticiferous canals of Decaisnea insignis fruits

Introduction

Programmed cell death (PCD) is a fundamental biological process crucial for plant development. Despite recent advancements in our understanding of PCD's molecular mechanisms, the intricate orchestration of this process within plant cells remains enigmatic. To address this knowledge gap, the present study focuses on Decaisnea insignis, a plant species renowned for its unique fruit anatomy, including laticiferous canals that secrete latex. While extensive anatomical studies have elucidated the structural features of these canals,molecular insights into their developmental regulation, particularly the involvement of PCD, are lacking.

Methods

In this study, we sequenced the single-cell transcriptomes at two developmental stage of Decaisnea insignis fruit using the technology known as 10x Genomics (S1, S2). Using sequencing technology combining full- length RNA sequencing and single-nucleus RNA sequencing (snRNA-seq) in combination with ultrastructural analyses, our study revealed a cellular map of Decaisnea insignis fruit at the single-cell level and identified different cell types.

Results

In particular, we identified a possible PCD-mediated cluster of Decaisnea insignis fruit lactiferous canals in epidermal cells and clarified the expression patterns of DiRD21A (a hydrolase) and DiLSD1 (a transcription factor), which may be closely related to the development of laticiferous canals in Decaisnea insignis fruits.

Discussion

By integrating high-resolution gene expression profiling with visual insights into cellular transformations, we sought to more precisely characterize the regulatory role of PCD during the developmental formation of lactiferous canals in Decaisnea insignis fruit.

Ac-DEVD-CHO (caspase-3/DEVDase inhibitor) suppresses self-incompatibility-induced programmed cell death in the pollen tubes of petunia (Petunia hybrida E. Vilm.)

Programmed cell death (PCD) is relevant to many aspects in the growth and development of a plant organism. In their reproduction, many flowering plant species possess self-incompatibility (SI), that is an intraspecific reproductive barrier, which is a genetic mechanism ensuring the avoidance of inbreeding depression by preventing self-pollination. This phenomenon enhances intraspecific variation; however, SI is rather a hindrance for some fruit plant species (such as plum, cherry, and peer trees) rather than an advantage in farming. PCD is a factor of the S-RNase-based SI in Petunia hybrida E. Vilm. The growth of self-incompatible pollen tubes (PTs) is arrested with an increase in the activity of caspase-like proteases during the first hours after pollination so that all traits of PCD-plasma membrane integrity damage, DNA degradation/disintegration, and damage of PT structural organization (absence of vacuoles, turgor disturbance, and separation of cell plasma membrane from the cell wall)-are observable by the moment of PT growth arrest. We succeeded in discovering an additional cytological PCD marker, namely, the formation of ricinosomes in self-incompatible PTs at early stages of PCD. SI is removable by treating petunia stigmas with Acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO), an inhibitor of caspase-3/DEVDase, 2 h before a self-incompatible pollination. In this process, the level of caspase-3-like protease activity was low, DNA degradation was absent, PTs grew to the ovary, fertilization was successful, and full-fledged seeds were formed.