Tapetum Development Research Articles

Gene expression profiles and metabolic pathways responsible for male sterility in cybrid pummelo.

Abnormal expression of genes regulating anther and pollen development and insufficient accumulation of male sterility (MS)- related metabolites lead to MS in cybrid pummelo Male sterility (MS) is a major cause of seedlessness in citrus, which is an important trait for fresh fruit. Understanding the mechanism of MS is important for breeding seedless citrus cultivars. In this study, we dissected the transcriptional, metabolic and physiological mechanisms of MS in somatic cybrid of pummelo (G1 + HBP). G1 + HBP exhibited severe male sterility, manifesting as retarded anther differentiation, abnormal anther wall development (especially tapetum and endothecium), and deficient pollen wall formation. In the anthers of G1 + HBP, the expression of genes regulating anther differentiation and tapetum development was abnormal, and the expression of genes regulating endothecium secondary lignification thickening and pollen wall formation was down-regulated. The transcription of genes involved in MS-related biological processes, such as jasmonic acid (JA) signaling pathway, primary metabolism, flavonoid metabolism, and programmed cell death, was altered in G1 + HBP anthers, and the accumulation of MS-associated metabolites, including fatty acids, amino acids, sugars, ATP, flavonols and reactive oxygen species (ROS), was down-regulated in G1 + HBP anthers. In summary, abnormal expression of key genes regulating anther and pollen development, altered transcription of key genes involved in MS-related metabolic pathways, and insufficient accumulation of MS-related metabolites together lead to MS in G1 + HBP. The critical genes and the metabolism pathways identified herein provide new insights into the formation mechanism of MS in citrus and candidate genes for breeding seedless citrus.

The BNB-GLID module regulates germline fate determination in Marchantia polymorpha.

Germline fate determination is a critical event in sexual reproduction. Unlike animals, plants specify the germline by reprogramming somatic cells at the late stages of their development. However, the genetic basis of germline fate determination and how it evolved during the land plant evolution are still poorly understood. Here, we report that the plant homeodomain finger protein GERMLINE IDENTITY DETERMINANT (GLID) is a key regulator of the germline specification in liverwort, Marchantia polymorpha. Loss of the MpGLID function causes failure of germline initiation, leading to the absence of sperm and egg cells. Remarkably, the overexpression of MpGLID in M. polymorpha induces the ectopic formation of cells with male germline cell features exclusively in male thalli. We further show that MpBONOBO (BNB), with an evolutionarily conserved function, can induce the formation of male germ cell-like cells through the activation of MpGLID by directly binding to its promoter. The Arabidopsis (Arabidopsis thaliana) MpGLID ortholog, MALE STERILITY1 (AtMS1), fails to replace the germline specification function of MpGLID in M. polymorpha, demonstrating that a derived function of MpGLID orthologs has been restricted to tapetum development in flowering plants. Collectively, our findings suggest the presence of the BNB-GLID module in complex ancestral land plants that has been retained in bryophytes, but rewired in flowering plants for male germline fate determination.

Ultraviolet attenuates centromere-mediated meiotic genome stability and alters gametophytic ploidy consistency in flowering plants.

Ultraviolet (UV) radiation influences development and genome stability in organisms; however, its impact on meiosis, a special cell division essential for the delivery of genetic information across generations in eukaryotes, has not yet been elucidated. In this study, by performing cytogenetic studies, we reported that UV radiation does not damage meiotic chromosome integrity but attenuates centromere-mediated chromosome stability and induces unreduced gametes in Arabidopsis thaliana. We showed that functional centromere-specific histone 3 (CENH3) is required for obligate crossover formation and plays a role in the protection of sister chromatid cohesion under UV stress. Moreover, we found that UV specifically alters the orientation and organization of spindles and phragmoplasts at meiosis II, resulting in meiotic restitution and unreduced gametes. We determined that UV-induced meiotic restitution does not rely on the UV Resistance Locus8-mediated UV perception and the Tapetal Development and Function1- and Aborted Microspores-dependent tapetum development, but possibly occurs via altered JASON function and downregulated Parallel Spindle1. This study provides evidence that UV radiation influences meiotic genome stability and gametophytic ploidy consistency in flowering plants.

In-Depth Understanding of Cytoplasmic Male Sterility by Metabolomics in Spring Stem Mustard (Brassica juncea var. tumida Tsen et Lee)

Male sterility (MS) caused by aborted pollen is a vital germplasm resource. In this study, metabolomic, transcriptomic, and proteomic analyses were performed to investigate the molecular regulatory mechanism of cytoplasmic male sterility (CMS) in the flower buds of the male sterile line 09-05A and its maintainer line, 09-05B, of Brassica juncea. Our metabolomic analysis revealed that 41 metabolites involved in pollen development and male fertility formation were differentially accumulated between 09-05A and 09-05B at the bi-nucleate stage of B. juncea. Integrated omics indicated that the expression of key genes and proteins in the amino acid and phenylpropanoid metabolic pathways was remarkably downregulated in the flower buds of 09-05A. Furthermore, the abnormal expression of key transcription factor (TF) genes related to tapetum development and pollen wall formation may affect pollen development in the 09-05A CMS line. The results indicated that the downregulated expression level of critical genes and proteins in amino acid metabolism; phenylpropanoid synthesis; and TF genes, such as shikimate kinase, phenylalanine ammonia-lyase, and MYB103, may have led to impaired tapetum and pollen wall development, thereby causing pollen abortion in 09-05A. This study provides new insights into the metabolic and molecular regulatory mechanisms underlying the formation of CMS in B. juncea and lays a foundation for detailed studies on the identity and characteristics of MS-related genes.

MS2/GmAMS1 encodes a bHLH transcription factor important for tapetum degeneration in soybean.

GmAMS1 is the only functional AMS and works with GmTDF1-1 and GmMS3 to orchestrate the tapetum degeneration in soybean. Heterosis could significantly increase the production of major crops as well as soybean [Glycine max (L.) Merr.]. Stable male-sterile/female-fertile mutants including ms2 are useful resources to apply in soybean hybrid production. Here, we identified the detailed mutated sites of two classic mutants ms2 (Eldorado) and ms2 (Ames) in MS2/GmAMS1 via the high-throughput sequencing method. Subsequently, we verified that GmAMS1, a bHLH transcription factor, is the only functional AMS member in soybean through the complementary experiment in Arabidopsis; and elucidated the dysfunction of its homolog GmAMS2 is caused by the premature stop codon in the gene's coding sequence. Further qRT-PCR analysis and protein-protein interaction assays indicated GmAMS1 is required for expressing downstream members in the putative DYT1-TDF1-AMS-MYB80/MYB103/MS188-MS1 cascade module, and might regulate the upstream members in a feedback mechanism. GmAMS1 could interact with GmTDF1-1 and GmMS3 via different region, which contributes to dissect the mechanism in the tapetum degeneration process. Additionally, as a core member in the conserved cascade module controlling the tapetum development and degeneration, AMS is conservatively present in all land plant lineages, implying that AMS-mediated signaling pathway has been established before land plants diverged, which provides further insight into the tapetal evolution.

The characteristic analysis of TaTDF1 reveals its function related to male sterility in wheat (Triticum aestivum L.)

BackgroundThe male sterile lines are an important foundation for heterosis utilization in wheat (Triticum aestivum L.). Thereinto, pollen development is one of the indispensable processes of wheat reproductive development, and its fertility plays an important role in wheat heterosis utilization, and are usually influencing by genes. However, these key genes and their regulatory networks during pollen abortion are poorly understood in wheat.ResultsDEFECTIVE IN TAPETAL DEVELOPMENT AND FUNCTION 1 (TDF1) is a member of the R2R3-MYB family and has been shown to be essential for early tapetal layer development and pollen grain fertility in rice (Oryza sativa L.) and Arabidopsis thaliana. In order to clarify the function of TDF1 in wheat anthers development, we used OsTDF1 gene as a reference sequence and homologous cloned wheat TaTDF1 gene. TaTDF1 is localized in the nucleus. The average bolting time of Arabidopsis thaliana overexpressed strain (TaTDF1-OE) was 33 d, and its anther could be colored normally by Alexander staining solution, showing red. The dominant Mosaic suppression silence-line (TaTDF1-EAR) was blue-green in color, and the anthers were shrimpy and thin. The TaTDF1 interacting protein (TaMAP65) was confirmed using Yeast Two-Hybrid Assay (Y2H) and Bimolecular-Fluorescence Complementation (BiFC) experiments. The results showed that downregulated expression of TaTDF1 and TaMAP65 could cause anthers to be smaller and shrunken, leading to pollen abortion in TaTDF1 wheat plants induced by virus-induced gene-silencing technology. The expression pattern of TaTDF1 was influenced by TaMAP65.ConclusionsThus, systematically revealing the regulatory mechanism of wheat TaTDF1 during anther and pollen grain development may provide new information on the molecular mechanism of pollen abortion in wheat.

Advance in the anther tapetum development and their regulatory mechanisms

Advance in the anther tapetum development and their regulatory mechanisms

Abnormal Degraded Tapetum1 (ADT1) is required for tapetal cell death and pollen development in rice.

The timely degradation of tapetum, the innermost somatic anther cell layer in flowering plants, is critical for pollen development. Although several genes involved in tapetum development have been characterized, the molecular mechanisms underlying tapetum degeneration remain elusive. Here, we showed that mutation in Abnormal Degraded Tapetum1 (ADT1)resulted in overaccumulation of Reactive Oxygen Species (ROS) and abnormal anther development, causing earlier tapetum Programmed Cell Death (PCD) and pollen abortion. ADT1 encodes a nuclear membrane localized protein, which is strongly expressed in the developing microspores and tapetal cells during early anther development. Moreover, ADT1 could interact with metallothionein MT2b, which was related to ROS scavenging and cell death regulation. These findings indicate that ADT1 is required for proper timing of tapetum PCD by regulating ROS homeostasis, expanding our understanding of the regulatory network of male reproductive development in rice.

Sporophytic control of tapetal development and pollen fertility by a mitogen-activated protein kinase cascade in rice.

Tapetum, the innermost layer of the anther wall, provides essential nutrients and materials for pollen development. Timely degradation of anther tapetal cells is a prerequisite for normal pollen development in flowering plants. Tapetal cells facilitate male gametogenesis by providing cellular contents after highly coordinated programmed cell death (PCD). Tapetal development is regulated by a transcriptional network. However, the signaling pathway(s) involved in this process are poorly understood. In this study, we report that a mitogen-activated protein kinase (MAPK) cascade composed of OsYDA1/OsYDA2-OsMKK4-OsMPK6 plays an important role in tapetal development and male gametophyte fertility. Loss of function of this MAPK cascade leads to anther indehiscence, enlarged tapetum, and aborted pollen grains. Tapetal cells in osmkk4 and osmpk6 mutants exhibit an increased presence of lipid body-like structures within the cytoplasm, which is accompanied by a delayed occurrence of PCD. Expression of a constitutively active version of OsMPK6 (CA-OsMPK6) can rescue the pollen defects in osmkk4 mutants, confirming that OsMPK6 functions downstream of OsMKK4 in this pathway. Genetic crosses also demonstrated that the MAPK cascade sporophyticly regulates pollen development. Our study reveals a novel function of rice MAPK cascade in plant male reproductive biology.

OsALKBH9-mediated m6A demethylation regulates tapetal PCD and pollen exine accumulation in rice.

The N6-methyladenosine (m6A) mRNA modification is crucial for plant development and stress responses. In rice, the male sterility resulting from the deficiency of OsFIP37, a core component of m6A methyltransferase complex, emphasizes the significant role of m6A in male fertility. m6A is reversible and can be removed by m6A demethylases. However, whether mRNA m6A demethylase regulates male fertility in rice has remained unknown. Here, we identify the mRNA m6A demethylase OsALKBH9 and demonstrate its involvement in male fertility regulation. Knockout of OsALKBH9 causes male sterility, dependent on its m6A demethylation activity. Cytological analysis reveals defective tapetal programmed cell death (PCD) and excessive accumulation of microspores exine in Osalkbh9-1. Transcriptome analysis of anthers shows up-regulation of genes involved in tapetum development, sporopollenin synthesis, and transport pathways in Osalkbh9-1. Additionally, we demonstrate that OsALKBH9 demethylates the m6A modification in TDR and GAMYB transcripts, which affects the stability of these mRNAs and ultimately leads to excessive accumulation of pollen exine. Our findings highlight the precise control of mRNA m6A modification and reveal the pivotal roles played by OsALKBH9-mediated m6A demethylation in tapetal PCD and pollen exine accumulation in rice.

The vesicle trafficking gene, OsRab7, is critical for pollen development and male fertility in cytoplasmic male-sterility rice

Rice cytoplasmic male sterility (CMS) provides an exceptional model for studying genetic interaction within plant nuclei given its inheritable trait of non-functional male gametophyte. Gaining a comprehensive understanding of the genes and pathways associated with the CMS mechanism is imperative for improving the vigor of hybrid rice agronomically, such as its productivity. Here, we observed a significant decrease in the expression of a gene named OsRab7 in the anther of the CMS line (SJA) compared to the maintainer line (SJB). OsRab7 is responsible for vesicle trafficking and loss function of OsRab7 significantly reduced pollen fertility and setting rate relative to the wild type. Meanwhile, over-expression of OsRab7 enhanced pollen fertility in the SJA line while a decrease in its expression in the SJB line led to the reduced pollen fertility. Premature tapetum and abnormal development of microspores were observed in the rab7 mutant. The expression of critical genes involved in tapetum development (OsMYB103, OsPTC1, OsEAT1 and OsAP25) and pollen development (OsMSP1, OsDTM1 and OsC4) decreased significantly in the anther of rab7 mutant. Reduced activities of the pDR5::GUS marker in the young panicle and anther of the rab7 mutant were also observed. Furthermore, the mRNA levels of genes involved in auxin biosynthesis (YUCCAs), auxin transport (PINs), auxin response factors (ARFs), and members of the IAA family (IAAs) were all downregulated in the rab7 mutant, indicating its impact on auxin signaling and distribution. In summary, these findings underscore the importance of OsRab7 in rice pollen development and its potential link to cytoplasmic male sterility.

Acyl-CoA synthetase 1 plays an important role on pollen development and male fertility in tomato

The development of pollen is critical to male reproduction in flowering plants. Acyl-CoA synthetase (ACOS) genes play conserved functions in regulating pollen development in various plants. Our previous work found that knockout of the SlACOS1 gene in tomato might decrease fruit setting. The current study further revealed that SlACOS1 was important to pollen development and male fertility. The SlACOS1 gene was preferentially expressed in the stamen of the flower with the highest expression at the tetrad stage of anther development. Mutation of the SlACOS1 gene by the CRISPR/Cas9-editing system reduced pollen number and viability as well as fruit setting. The tapetum layer exhibited premature degradation and the pollen showed abnormal development appearing irregular, shriveled, or anucleate in Slacos1 mutants at the tetrad stage. The fatty acid metabolism in anthers was significantly impacted by mutation of the SlACOS1 gene. Furthermore, targeted fatty acids profiling using GC-MS found that contents of most fatty acids except C18:1 and C18:2 were reduced. Yeast complementation assay demonstrated that the substrate preferences of SlACOS1 were C16:0 and C18:0 fatty acids. Male fertility of Slacos1 mutant could be slightly restored by applying exogenous palmitic acid, a type of C16:0 fatty acid. Taken together, SlACOS1 played important roles on pollen development and male fertility by regulating the fatty acid metabolism and the development of tapetum and tetrad. Our findings will facilitate unraveling the mechanism of pollen development and male fertility in tomato.

ClBBM and ClPLT2 function redundantly during both male and female gametophytes development in watermelon

As a prerequisite for sexual reproduction, gametophyte development is an interesting process involving cell proliferation, differentiation and specialization. Gametogenesis has been extensively explored in model plants, but the regulatory mechanism of gametophyte development largely remains unknown in Cucurbitaceae species. In present study, we have shown that watermelon ClBBM and ClPLT2, two AP2/ERF transcription factors, participated in both male and female gametophyte development. Clbbm and Clplt2 single mutants resembled wild-type phenotypes in both vegetative and reproductive development. But Clbbm/Clplt2 double mutant showed partial pollen abortion and bore less seeds comparing to WT. Our results indicated that the abnormal pollen grains were caused by premature tapetum degeneration, and reduced seed-set was due to faulty embryo sac development. ClBBM and ClPLT2 were expressed in FG4 embryo sacs, and their transcripts were also detectable in the tapetum and microspore of stage 9 anthers, which was consistent with developmental stages of defective phenotypes observed in double mutant. The expression of genes essential for tapetum development, ClATM1, ClAMS, ClMS1 and ClMS188, was decreased in Clbbm/Clplt2 double mutants. Moreover, the transcriptome analysis indicated that ClBBM and ClPLT2 participated in tapetum and pollen wall development by regulate cell cycle, transmembrane transport, glucan and cellulose metabolic process. Collectively, ClBBM and ClPLT2 were functionally redundant in regulating gametophyte development in watermelon, and their functions differ from their homologous genes in model plant Arabidopsis.

The haplotype-resolved autotetraploid genome assembly provides insights into the genomic evolution and fruit divergence in wax apple (Syzygium samarangense (Blume) Merr. and Perry)

Abstract Wax apple (Syzygium samarangense) is an economically important fruit crop with great potential value to human health because of its richness in antioxidant substances. Here, we present a haplotype-resolved autotetraploid genome assembly of the wax apple with a size of 1.59 Gb. Comparative genomic analysis revealed three rounds of whole-genome duplication (WGD) events, including two independent WGDs after WGT-γ. Resequencing analysis of 35 accessions partitioned these individuals into two distinct groups, including 28 landraces and seven cultivated species, and several genes subject to selective sweeps possibly contributed to fruit growth, including the KRP1-like, IAA17-like, GME-like, and FLACCA-like genes. Transcriptome analysis of three different varieties during flower and fruit development identified key genes related to fruit size, sugar content, and male sterility. We found that AP2 also affected fruit size by regulating sepal development in wax apples. The expression of sugar transport-related genes (SWEETs and SUTs) was high in ‘ZY’, likely contributing to its high sugar content. Male sterility in ‘Tub’ was associated with tapetal abnormalities due to the decreased expression of DYT1, TDF1, and AMS, which affected early tapetum development. The chromosome-scale genome and large-scale transcriptome data presented in this study offer new valuable resources for biological research on S. samarangense and shed new light on fruit size control, sugar metabolism, and male sterility regulatory metabolism in wax apple.

Barley TAPETAL DEVELOPMENT and FUNCTION1 (HvTDF1) gene reveals conserved and unique roles in controlling anther tapetum development in dicot and monocot plants.

The anther tapetum helps control microspore release and essential components for pollen wall formation. TAPETAL DEVELOPMENT and FUNCTION1 (TDF1) is an essential R2R3 MYB tapetum transcription factor in Arabidopsis thaliana; however, little is known about pollen development in the temperate monocot barley. Here, we characterize the barley (Hordeum vulgare L.) TDF1 ortholog using reverse genetics and transcriptomics. Spatial/temporal expression analysis indicates HvTDF1 has tapetum-specific expression during anther stage 7/8. Homozygous barley hvtdf1 mutants exhibit male sterility with retarded tapetum development, delayed tapetum endomitosis and cell wall degeneration, resulting in enlarged, vacuolated tapetum surrounding collapsing microspores. Transient protein expression and dual-luciferase assays show TDF1 is a nuclear-localized, transcription activator, that directly activates osmotin proteins. Comparison of hvtdf1 transcriptome data revealed several pathways were delayed, endorsing the observed retarded anther morphology. Arabidopsis tdf1 mutant fertility was recovered by HvTDF1, supporting a conserved role for TDF1 in monocots and dicots. This indicates that tapetum development shares similarity between monocot and dicots; however, barley HvTDF1 appears to uniquely act as a modifier to activate tapetum gene expression pathways, which are subsequently also induced by other factors. Therefore, the absence of HvTDF1 results in delayed developmental progression rather than pathway failure, although inevitably still results in pollen degeneration.

Comparative cytological and transcriptome analyses of ny2 mutant delayed degeneration of tapetal cells and promotes abnormal microspore development in neo-tetraploid rice.

We aimed to investigate the genetic defects related to pollen development and infertility in NY2, a novel tetraploid rice germplasm known as Neo-tetraploid rice. This rice variety was created through the crossbreeding and selective breeding of various autotetraploid rice lines and has previously shown high fertility. Our previous research has revealed that the NY2 gene, encoding a eukaryotic translation initiation factor 3 subunit E, regulates pollen fertility. However, the underlying mechanism behind this fertility is yet to be understood. To shed light on this matter, we performed a combined cytological and transcriptome analysis of the NY2 gene. Cytological analysis indicated that ny2 underwent abnormal tapetal cells, microspore, and middle layer development, which led to pollen abortion and ultimately to male sterility. Genetic analysis revealed that the F1 plants showed normal fertility and an obvious advantage for seed setting compared to ny2. Global gene expression analysis in ny2 revealed a total of 7545 genes were detected at the meiosis stage, and 3925 and 3620 displayed upregulation and downregulation, respectively. The genes were significantly enriched for the gene ontology (GO) term "carbohydrate metabolic process. Moreover, 9 genes related to tapetum or pollen fertility showed down-regulation, such as OsABCG26 (ATP Binding Cassette G26), TMS9-1 (Thermosensitive Male Sterility), EAT1 (Programmed cell death regulatory), KIN14M (Kinesin Motor), OsMT1a (Metallothionein), and OsSTRL2 (Atypical strictosidine synthase), which were validated by qRT-PCR. Further analyses of DEGs identified nine down-regulated transcription factor genes related to pollen development. NY2 is an important regulator of the development of tapetum and microspore. The regulatory gene network described in this study may offer important understandings into the molecular processes that underlie fertility control in tetraploid rice.

Knockout of floral and meiosis genes using CRISPR/Cas9 produces male-sterility in Eucalyptus without impacts on vegetative growth.

Eucalyptus spp. are widely cultivated for the production of pulp, energy, essential oils, and as ornamentals. However, their dispersal from plantings, especially when grown as an exotic, can cause ecological disruptions. To provide new tools for prevention of sexual dispersal by pollen as well as to induce male-sterility for hybrid breeding, we studied the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated knockout of three floral genes in both FT-expressing (early-flowering) and non-FT genotypes. We report male-sterile phenotypes resulting from knockout of the homologs of all three genes, including one involved in meiosis and two regulating early stages of pollen development. The targeted genes were Eucalyptus homologs of REC8 (EREC8), TAPETAL DEVELOPMENT AND FUNCTION 1 (ETDF1), and HECATE3 (EHEC3-like). The erec8 knockouts yielded abnormal pollen grains and a predominance of inviable pollen, whereas the etdf1 and ehec3-like knockouts produced virtually no pollen. In addition to male-sterility, both erec8 and ehec3-like knockouts may provide complete sterility because the failure of erec8 to undergo meiosis is expected to be independent of sex, and ehec3-like knockouts produce flowers with shortened styles and no visible stigmas. When comparing knockouts to controls in wild-type (non-early-flowering) backgrounds, we did not find visible morphological or statistical differences in vegetative traits, including average single-leaf mass, stem volume, density of oil glands, or chlorophyll in leaves. Loss-of-function mutations in any of these three genes show promise as a means of inducing male- or complete sterility without impacting vegetative development.

Industrial chicory genome gives insights into the molecular timetable of anther development and male sterility.

Industrial chicory (Cichorium intybus var. sativum) is a biannual crop mostly cultivated for extraction of inulin, a fructose polymer used as a dietary fiber. F1 hybrid breeding is a promising breeding strategy in chicory but relies on stable male sterile lines to prevent self-pollination. Here, we report the assembly and annotation of a new industrial chicory reference genome. Additionally, we performed RNA-Seq on subsequent stages of flower bud development of a fertile line and two cytoplasmic male sterile (CMS) clones. Comparison of fertile and CMS flower bud transcriptomes combined with morphological microscopic analysis of anthers, provided a molecular understanding of anther development and identified key genes in a range of underlying processes, including tapetum development, sink establishment, pollen wall development and anther dehiscence. We also described the role of phytohormones in the regulation of these processes under normal fertile flower bud development. In parallel, we evaluated which processes are disturbed in CMS clones and could contribute to the male sterile phenotype. Taken together, this study provides a state-of-the-art industrial chicory reference genome, an annotated and curated candidate gene set related to anther development and male sterility as well as a detailed molecular timetable of flower bud development in fertile and CMS lines.

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.

Review on tapetal ultrastructure in angiosperms

The appearance of new cellular structures and characteristics in the tapetum suggests that there is still much to discover that would help to better understand the tapetum functions. The ultrastructure of the tapetum provides important information for the understanding of the functions performed by this tissue. Since there are no reviews on the subject, we aim to collect all the detailed information about the tapetum ultrastructure present until this moment in order to lay the foundations for future research. Detailed information on the tapetal ultrastructure of 80 species from 45 different families: 2 species with invasive non-syncytial tapetum, 11 with plasmodial and 67 with a secretory tapetum was collected. These studies allowed to establish (a) the most usual cytological characteristics of this tissue, (b) unique characteristics and/or cellular structures in tapetum cells, (c) the ultrastructural changes that occur in different types of tapetum, during the progress of microsporogenesis and microgametogenesis, and (d) the most recognized ultrastructural traits of the tapetum that cause androsterility. The structure of these cells is related to their function in each developmental stage. Since most species present their particular ultrastructure and may sometimes, share some traits within families, there is not a model plant on tapetum ultrastructure. However, knowing the general cytological aspect of the tapetum may help distinguish between patterns of cytoplasmic disorganization due to tapetum degeneration from technical failures of the preparation. Moreover, as the amount of species analyzed increases, unknown tapetal organelles or traits may be identified that might be associated to particular functions of this tissue. On the other hand, different ultrastructural changes may be related to the metabolisms and the regulation of normal/abnormal tapetum development.