Degradation Of Tapetum Research Articles

PsEND1 Is a Key Player in Pea Pollen Development Through the Modulation of Redox Homeostasis.

Redox homeostasis has been linked to proper anther and pollen development. Accordingly, plant cells have developed several Reactive Oxygen Species (ROS)-scavenging mechanisms to maintain the redox balance. Hemopexins constitute one of these mechanisms preventing heme-associated oxidative stress in animals, fungi, and plants. Pisum sativum ENDOTHECIUM 1 (PsEND1) is a pea anther-specific gene that encodes a protein containing four hemopexin domains. We report the functional characterization of PsEND1 and the identification in its promoter region of cis-regulatory elements that are essential for the specific expression in anthers. PsEND1 promoter deletion analysis revealed that a putative CArG-like regulatory motif is necessary to confer promoter activity in developing anthers. Our data suggest that PsEND1 might be a hemopexin regulated by a MADS-box protein. PsEND1 gene silencing in pea, and its overexpression in heterologous systems, result in similar defects in the anthers consisting of precocious tapetum degradation and the impairment of pollen development. Such alterations were associated to the production of superoxide anion and altered activity of ROS-scavenging enzymes. Our findings demonstrate that PsEND1 is essential for pollen development by modulating ROS levels during the differentiation of the anther tissues surrounding the microsporocytes.

ZRT-IRT-Like PROTEIN 6 expression perturbs local ion homeostasis in flowers and leads to anther indehiscence and male sterility.

Metallic micronutrients are essential throughout the plant life cycle. Maintaining metal homeostasis in plant tissues requires a highly complex and finely tuned network controlling metal uptake, transport, distribution and storage. Zinc and cadmium hyperaccumulation, such as observed in the model plant Arabidopsis halleri, represents an extreme evolution of this network. Here, non-ectopic overexpression of the A. halleri ZIP6 (AhZIP6) gene, encoding a zinc and cadmium influx transporter, in Arabidopsis thaliana enabled examining the importance of zinc for flower development and reproduction. We show that AhZIP6 expression in flowers leads to male sterility resulting from anther indehiscence in a dose-dependent manner. The sterility phenotype is associated to delayed tapetum degradation and endothecium collapse, as well as increased magnesium and potassium accumulation and higher expression of the MHX gene in stamens. It is rescued by the co-expression of the zinc efflux transporter AhHMA4, linking the sterility phenotype to zinc homeostasis. Altogether, our results confirm that AhZIP6 is able to transport zinc in planta and highlight the importance of fine-tuning zinc homeostasis in reproductive organs. The study illustrates how the characterization of metal hyperaccumulation mechanisms can reveal key nodes and processes in the metal homeostasis network.

OsEDM2L mediates m6 A of EAT1 transcript for proper alternative splicing and polyadenylation regulating rice tapetal degradation.

N6 -methyladenosine (m6 A) modification affects the post-transcriptional regulation of eukaryotic gene expression, but the underlying mechanisms and their effects in plants remain largely unknown. Here, we report that the N6 -adenine methyltransferase-like domain-containing protein ENHANCED DOWNY MILDEW 2-LIKE (OsEDM2L) is essential for rice (Oryza sativa L.) anther development. The osedm2l knockout mutant showed delayed tapetal programmed cell death (PCD) and defective pollen development. OsEDM2L interacts with the transcription factors basic helix-loop-helix 142 and TAPETUM DEGENERATION RETARDATION to regulate the expression of ETERNAL TAPETUM 1 (EAT1), a positive regulator of tapetal PCD. Mutation of OsEDM2L altered the transcriptomic m6 A landscape, and caused a distinct m6 A modification of the EAT1 transcript leading to dysregulation of its alternative splicing and polyadenylation, followed by suppression of the EAT1 target genes OsAP25 and OsAP37 for tapetal PCD. Therefore, OsEDM2L is indispensable for proper messenger RNA m6 A modification in rice anther development.

GhGPAT12/25 Are Essential for the Formation of Anther Cuticle and Pollen Exine in Cotton (Gossypium hirsutum L.).

Glycerol-3-phosphate acyltransferases (GPATs), critical for multiple biological processes like male fertility, have been extensively characterized. However, their precise functions and underlying regulatory mechanism in cotton anther development are unclear. This research demonstrated the importance of GhGPAT12/25 (a paralogs pair on A12/D12 sub-chromosome of cotton) to regulate the degradation of tapetum, anther cuticle formation, and pollen exine development. GhGPAT12 and GhGPAT25 exhibited specifically detected transcripts in tapetum and pollen exine during the early anther developmental stages. GhGPAT12/25 are sn-2 glycerol-3-phosphate acyltransferases and can transfer the acyl group of palmitoyl-CoA to glycerol-3-phosphate (G3P). CRISPR/Cas9-mediated knockout identified the functional redundancy of GhGPAT12 and GhGPAT25. Knockout of both genes caused completely male sterility associated with abnormal anther cuticle, swollen tapetum, and inviable microspores with defective exine and irregular unrestricted shape. RNA-seq analysis showed that the loss of function of GhGPAT12/25 affects the processes of wax metabolic, glycerol monomer biosynthesis, and transport. Consistently, cuticular waxes were dramatically reduced in mutant anthers. Yeast one-hybrid system (Y1H), virus-induced gene silencing (VIGS), and dual-luciferase (LUC) assays illustrated that GhMYB80s are likely to directly activate the expression of GhGPAT12/25. This study provides important insights for revealing the regulatory mechanism underlying anther development in cotton.

Pollen development in three selected species of Rubiaceae provides ontogenetic evidence for pollen evolution

Pollen development in Ixora chinensis, Pentas lanceolata, and Spermacoce pusilla was investigated. Simultaneous cytokinesis at meiosis, a persistent epidermis, fibrous thickenings in the endothecium, an ephemeral middle layer, and a secretory tapetum that remains uninucleate were observed in all examined species and constitute a family character in Rubiaceae. The main ontogenetic sequence of sporoderm development is generally centripetal and shows major similarities among the studied species, with slight differences in the timing of specific events. Tapetum degradation starts slightly later in I. chinensis than in P. lanceolata and S. pusilla, while intine formation may be slightly later in S. pusilla than in the other two species. Occurrences of orbicules, white-line-centered endexine lamellae and apertural intine projections were observed in I. chinensis and P. lanceolata but not in S. pusilla. Columellae are well-developed in I. chinensis and P. lanceolata but are simplified in S. pusilla. Carbohydrate reserves in mature pollen grains also vary among these three species. Thickened endexine at the apertural sites and a membranous granular layer are shared by the three species. White-line-centered lamellae might represent a common mechanism for endexine formation in the family. Endexine dilations and thickening occurred in the apertural region represent a common character in the family. The ephemeral membranous granular layer developed beneath the endexine is a very common feature for Rubiaceae. Our study shows that ultrastructural and developmental studies are essential in illustrating micromorphological features of pollen especially these ephemeral characters. Thus, application of palynological ontogenetic data to phylogenetic problems deserves more attention.

Insight into the petunia Dof transcription factor family reveals a new regulator of male-sterility

Petunia hybrida is a hybrid ornamental that serves as one of the most popular bedding plants in the world. Numerous petunia seeds are distributed on an annual basis, which requires labor-intensive hybrid-breeding. The Dof (DNA-binding with one finger) transcription factor family is a plant-specific member of the zinc finger superfamily. Dofs play diverse roles in regulating plant developmental processes; however, their functions during flower development are not well characterized, especially in ornamental species. In this study, we used genome-wide analysis to identify 35 Dof genes that are encoded in the P. inflata reference genome. These Petunia Dofs (PiDofs) can be organized into five distinct phylogenetic groups, based on the sequences of their highly conserved Dof domains. Expression analysis using quantitative-RT-PCR identified several PiDofs that exhibit unique expression patterns during reproductive development. Many of these reproductive PiDofs were expressed in all four floral whorls throughout flower development, while other PiDofs exhibited developmental stage and/or organ specific expression patterns. RNAi was used to knock-down the expression level of PiDof14, an anther-specific Dof. Reduced expression of PiDof14 promoted tapetum degradation and depressed meiotic divisions in the microsporocytes, ultimately leading to a male-sterile phenotype. The organ- and stage-specific expression patterns of many of the other PiDof genes indicate that additional members of this family may play specific roles in regulating male and female fertility. This work provides insight into a novel regulator of male-fertility in Petunia, and lays the foundation for targeted genome engineering of the larger Dof family in order to generate an efficient hybrid breeding system for P. hybrida.

Retraction Note: Cloning and characterization of TaPUB4, a U-box gene from common wheat (Triticum aestivum L.) involved in regulation of pollen development by influencing sucrose-starch pathway in anther

Development of functional pollen grains in plants is regulated through complex genetic networks and environmental clues. The ubiquitin-26S proteasome system is important in the post-translational modification of intracellular proteins, and the system includes the ubiquitin activating (E1), ubiquitin conjugating (E2), and ubiquitin ligase (E3) enzymes. Here, a novel plant U-box-containing cDNA was isolated in anther from common wheat (Triticum aestivum) and designed as TaPUB4. The cDNA encoding comprised 2598 bp, with an open reading frame of 865 amino acids. The deduced amino acid sequence of TaPUB4 showed 41.2–92.3% identity with other plant U-box homologous genes. Self-ubiquitination assay indicated that the bacterially expressed TaPUB4 protein had E3 ligase activity, and subcellular localization results showed that TaPUB4 was located in the nucleus and cytoplasm in onion epidermal cells. Overexpression of TaPUB4 gene in Arabidopsis atpub4 mutant restored partially the fertility of the mutant, increased the number of pollens in anthers, enhanced pollen viability, and displayed normal degradation of tapetum as anther development. The expression levels of genes related to starch deposition also changed greatly in the anthers of transgenic lines. These results support the notion that as a homolog of AtPUB4, TaPUB4 might control male fertility by regulating sucrose-starch metabolism in pollen grains, and this process may be accomplished through ubiquitin-proteasome system. The development and utilization of TaPUB4 as a functional molecular marker may be helpful for improving its fertility in wheat breeding programs in the future.

Lipid metabolism is involved in male fertility regulation of the photoperiod- and thermo sensitive genic male sterile rice line Peiai 64S

Peiai 64S (PA64S) is a photoperiod- and thermo sensitive genic male sterile (PTGMS) rice line that has been widely applied in two-line hybrid rice breeding. The male fertility mechanism of PTGMS has always been the research focus. We obtained fertile PA64S (F) and sterile fertile PA64S (S) plants at 21℃ and 28℃, respectively. Here, we analyzed the development of anthers and pollen grains of PA64S (S) and found that the degradation of tapetum and sporopollenin accumulation of pollen exine was abnormal. The content of lipid components in PA64S (F) and PA64S (S) were different by LC–MS, among which sterols, (O-acyl) ω-hydroxy fatty acids, ceramide, and other lipid components were upregulated in PA64S (F). The results of transcriptome showed that many significantly different genes were enriched in the lipid metabolism pathways. Additionally, lipid synthesis and transport genes were downregulated in PA64S (S). In summary, the differences of the PA64S fertility under different temperatures were analyzed through multi-levels comparison. These results suggest that lipid synthesis and transport during PA64S anther development affects the lipid accumulation of pollen exine, and ultimately affected fertility. The differences in lipids content may also be a factor affecting PA64S pollen fertility.

Characterization and transcriptome analysis of a dominant genic male sterile cotton mutant

BackgroundMale sterility is an efficient trait for hybrid seed production and germplasm innovation. Until now, most studies on male sterility were on cytoplasmic and recessive genic sterility, with few on dominant genic male sterility, especially in cotton, due to lack of such mutant.ResultsWe discovered a natural male sterile (MS) Sea Island cotton (G. barbadense) mutant. Genetic analysis showed the mutation was caused by a dominant mutation in a single nuclear gene. Comparative cytological observation of anther sections from MS and wild-type (WT) uncovered cellular differences in anther at and after the tetrad stage of pollen mother cells (PMC). In the MS anthers, the outer wall of pollen grains was free of spinules, the tapetum was vacuolated and showed delayed degradation, consequently, no functional pollen grains. Comparison of transcriptomes from meiosis, tetrad, mononuclear and binuclear pollen, and pollen maturation stages identified 13,783 non-redundant differentially expressed genes (DEGs) between MS and WT. Based on the number of DEGs, analyses of enriched GO terms and KEGG pathways, it was evident that significant transcriptomic changes occurred at and after the tetrad stage, consistent with cytological observation, and that the major differences were on metabolism of starch, sucrose, ascorbate, aldarate, alanine, aspartate and glutamate, and biosynthesis of cutin, suberine and wax. WGCNA analysis identified five modules containing 920 genes highly related to anther development, especially the greenyellow module with 54 genes that was highly associated with PMC meiosis and tetrad formation. A NAC transcription factor (Gh_D11G2469) was identified as a hub gene for this module, which warrants further functional characterization.ConclusionsWe demonstrated that the MS trait was controlled by a single dominant nuclear gene and caused by delayed tapetum degradation at the tetrad stage. Comparative transcriptome analysis and gene network construction identified DEGs, enriched GO terms and metabolic pathways, and hub genes potentially associated with anther development and the MS trait. These results contribute to our understanding of dominant genic male sterility (DGMS) and provided source for innovation of cotton germplasm.

Differentially expressed miRNAs in anthers may contribute to the fertility of a novel Brassica napus genic male sterile line CN12A

In Brassica napus L. (rapeseed), complete genic male sterility (GMS) plays an important role in the utilization of heterosis. Although microRNAs (miRNAs) play essential regulatory roles during bud development, knowledge of how GMS is regulated by miRNAs in rapeseed is rather limited. In this study, we obtained a novel recessive GMS system, CN12AB. The sterile line CN12A has defects in tapetal differentiation and degradation. Illumina sequencing was employed to examine the expression of miRNAs in the buds of CN12A and the fertile line CN12B. We identified 85 known miRNAs and 120 novel miRNAs that were expressed during rapeseed anther development. When comparing the expression levels of miRNAs between CN12A and CN12B, 19 and 18 known miRNAs were found to be differentially expressed in 0.5–1.0 mm buds and in 2.5–3.0 mm buds, respectively. Among these, the expression levels of 14 miRNAs were higher and the levels of 23 miRNAs were lower in CN12A compared with CN12B. The predicted target genes of these differentially expressed miRNAs encode protein kinases, F-box domain-containing proteins, MADS-box family proteins, SBP-box gene family members, HD-ZIP proteins, floral homeotic protein APETALA 2 (AP2), and nuclear factor Y, subunit A. These targets have previously been reported to be involved in pollen development and male sterility, suggesting that miRNAs might act as regulators of GMS in rapeseed anthers. Furthermore, RT-qPCR data suggest that one of the differentially expressed miRNAs, bna-miR159, plays a role in tapetal differentiation by regulating the expression of transcription factor BnMYB101 and participates in tapetal degradation and influences callose degradation by manipulating the expression of BnA6. These findings contribute to our understanding of the roles of miRNAs during anther development and the occurrence of GMS in rapeseed.

Biological characteristics and cytological studies on anther abortion of male sterile <italic>Camellia crassocolumna</italic>

The purpose of this study was to explore the flower morphology, anther and pollen abortion time and its cytological characteristics in male sterile plants of C. crassocolumna . The flowering process, floral morphology, anther structure, meiosis and microsporogenesis of male sterile (M350) and fertile plants (M352) of C. crassocolumna were observed by stereomicroscopy, paraffin section, chromosome preparation and DAPI staining. The results showed that the wild tea plant had a perfect flower, its anthers were tetrasporangiate shaped like a butterfly, with an anther wall development of basic type. It tapetal cells were binuclear, forming secretory cells at the tetrad stage, and degrading during mononuclear pollen stage. After the meiosis I, meiosis II and cytokinesis, pollen mother cells developed into tetrahedral tetrads. Microspores were triangular, and mature pollen was two-celled. The stamens of male sterile flowers developed normally in the early stage of flower bud development, and there was no difference between sterile and fertile flowers, while in the late stage of flower bud development, filaments were curved, anthers adhered and shriveled, anthers could not release pollen. The tapetal cells of male sterile flowers were proliferation abnormally and disordly at the meiosis of stage pollen mother cells, and the degradation of tapetum was delayed during the mononuclear and binucleate pollen periods. During meiosis of pollen mother cells of male sterile flowers, there were some abnormal appearances, such as chromosome ring, lagging chromosomes, chromosome bridges, chromosomal deletion, scattered chromosomes, unequal separation, micronucleus and abnormal tetrad. In sterile plants, the microspore cytoplasm was disorder, pollen grains adhered to each other at the mononuclear stage, pollen wall crumpled and deformed, cytoplasm and nucleus of pollen were blurred, the mature pollen cells were hollow and sunken. Taken together, the floral organ morphology of male sterile plants in C. crassocolumna belongs to stamen collapse type and anther abnormality type. The development of anthers is blocked from meiosis of pollen mother cells to uninucleate pollen stage, belonging to pollen mother cell abortion type and uninucleate pollen abortion type. Mononuclear period is the main period of anther abortion. Tapetum degradation delayed, chromosomal abnormalities of pollen mother cells in meiosis, and abnormal development of microspores and pollens, might be the main reasons for anther abortion in male sterile plants of C. crassocolumna .

Impact of Autophagy on Gene Expression and Tapetal Programmed Cell Death During Pollen Development in Rice.

Autophagy has recently been shown to be required for tapetal programmed cell death (PCD) and pollen maturation in rice. A transcriptional regulatory network is also known to play a key role in the progression of tapetal PCD. However, the relationship between the gene regulatory network and autophagy in rice anther development is mostly unknown. Here, we comprehensively analyzed the effect of autophagy disruption on gene expression profile during the tapetal PCD in rice anther development using high-throughput RNA sequencing. Expression of thousands of genes, including specific transcription factors and several proteases required for tapetal degradation, fluctuated synchronously at specific stages during tapetal PCD progression in the wild-type anthers, while this fluctuation showed significant delay in the autophagy-deficient mutant Osatg7-1. Moreover, gene ontology enrichment analysis in combination with self-organizing map clustering as well as pathway analysis revealed that the expression patterns of a variety of organelle-related genes as well as genes involved in carbohydrate/lipid metabolism were affected in the Osatg7-1 mutant during pollen maturation. These results suggest that autophagy is required for proper regulation of gene expression and quality control of organelles and timely progression of tapetal PCD during rice pollen development.

Brassinosteroid-mediated reactive oxygen species are essential for tapetum degradation and pollen fertility in tomato.

Phytohormone brassinosteroids (BRs) are essential for plant growth and development, but the mechanisms of BR-mediated pollen development remain largely unknown. In this study, we show that pollen viability, pollen germination and seed number decreased in the BR-deficient mutant d^im , which has a lesion in the BR biosynthetic gene DWARF (DWF), and in the bzr1 mutant, which is deficient in BR signaling regulator BRASSINAZOLE RESISTANT1 (BZR1), compared with those in wild-type plants, whereas plants overexpressing DWF or BZR1 exhibited the opposite effects. Loss or gain of function in the DWF or BZR1 genes altered the timing of reactive oxygen species (ROS) production and programmed cell death (PCD) in tapetal cells, resulting in delayed or premature tapetal degeneration, respectively. Further analysis revealed that BZR1 could directly bind to the promoter of RESPIRATORY BURST OXIDASE HOMOLOG1 (RBOH1), and that RBOH1-mediated ROS promote pollen and seed development by triggering PCD and tapetal cell degradation. In contrast, the suppression of RBOH1 compromised BR signaling-mediated ROS production and pollen development. These findings provide strong evidence that BZR1-dependent ROS production plays a critical role in the BR-mediated regulation of tapetal cell degeneration and pollen development in Solanum lycopersicum (tomato) plants.

RMS2 Encoding a GDSL Lipase Mediates Lipid Homeostasis in Anthers to Determine Rice Male Fertility.

Plant male gametogenesis is a coordinated effort involving both reproductive tissues and sporophytic tissues, in which lipid metabolism plays an essential role. Although GDSL esterases/lipases have been well known as key enzymes for many plant developmental processes and stress responses, their functions in reproductive development remain unclear. Here, we report the identification of a rice male sterile2 (rms2) mutant in rice (Oryza sativa), which is completely male sterile due to the defects in tapetum degradation, cuticle formation in sporophytic tissues, and impaired exine and central vacuole development in pollen grains. RMS2 was map-based cloned as an endoplasmic reticulum-localized GDSL lipase gene, which is predominantly transcribed during early anther development. In rms2, a three-nucleotide deletion and one base substitution (TTGT to A) occurred within the GDSL domain, which reduced the lipid hydrolase activity of the resulting protein and led to significant changes in the content of 16 lipid components and numerous other metabolites, as revealed by a comparative metabolic analysis. Furthermore, RMS2 is directly targeted by the male fertility regulators Undeveloped Tapetum1 and Persistent Tapetal Cell1 both in vitro and in vivo, suggesting that RMS2 may serve as a key node in the rice male fertility regulatory network. These findings shed light on the function of GDSLs in reproductive development and provide a promising gene resource for hybrid rice breeding.

A point mutation in LTT1 enhances cold tolerance at the booting stage in rice.

The cold tolerance of rice at the booting stage is a main factor determining sustainability and regional adaptability. However, relatively few cold tolerance genes have been identified that can be effectively used in breeding programmes. Here, we show that a point mutation in the low‐temperature tolerance 1 (LTT1) gene improves cold tolerance by maintaining tapetum degradation and pollen development, by activation of systems that metabolize reactive oxygen species (ROS). Cold‐induced ROS accumulation is therefore prevented in the anthers of the ltt1 mutants allowing correct development. In contrast, exposure to cold stress dramatically increases ROS accumulation in the wild type anthers, together with the expression of genes encoding proteins associated with programmed cell death and with the accelerated degradation of the tapetum that ultimately leads to pollen abortion. These results demonstrate that appropriate ROS management is critical for the cold tolerance of rice at the booting stage. Hence, the ltt1 mutation can significantly improve the seed setting ability of cold‐sensitive rice varieties under low‐temperature stress conditions, with little yield penalty under optimal temperature conditions. This study highlights the importance of a valuable genetic resource that may be applied in rice breeding programmes to enhance cold tolerance.

Cytological observation of anther structure and genetic investigation of a thermo-sensitive genic male sterile line 373S in Brassica napus L

BackgroundPhotoperiod and/or thermo-sensitive male sterility is an effective pollination control system in crop two-line hybrid breeding. We previously discovered the spontaneous mutation of a partially male sterile plant and developed a thermo-sensitive genic male sterile (TGMS) line 373S in Brassica napus L. The present study characterized this TGMS line through cytological observation, photoperiod/ temperature treatments, and genetic investigation.ResultsMicroscopic observation revealed that the condensed cytoplasm and irregular exine of microspores and the abnormal degradation of tapetum are related to pollen abortion. Different temperature and photoperiod treatments in field and growth cabinet conditions indicated that the fertility alteration of 373S was mainly caused by temperature changes. The effects of photoperiod and interaction between temperature and photoperiod were insignificant. The critical temperature leading to fertility alteration ranged from 10 °C (15 °C/5 °C) to 12 °C (17 °C/7 °C), and the temperature-responding stage was coincident with anther development from pollen mother cell formation to meiosis stages. Genetic analysis indicated that the TGMS trait in 373S was controlled by one pair of genes, with male sterility as the recessive. Multiplex PCR analysis revealed that the cytoplasm of 373S is pol type.ConclusionsOur study suggested that the 373S line in B. napus has a novel thermo-sensitive gene Bnmst1 in Pol CMS cytoplasm background, and its fertility alteration is mainly caused by temperature changes. Our results will broaden the TGMS resources and lay the foundation for two-line hybrid breeding in B. napus.

Cytological abnormalities during pollen development in interspecific hybrids of Nicotiana

Nicotiana alata is resistant to Tomato spotted wilt virus (TSWV) and of great value in breeding. However, hybrid sterility constrains the application of interspecific genetic resources. Previously, we obtained interspecific hybrids between a cytoplasmic male sterility (CMS) line of Nicotiana tabacum and N. alata, some of which were pollen sterile. In the present research, we studied the cytological abnormalities during pollen development in sterile hybrids (F1-D) by comparing pollen development with that in fertile hybrids (F1-S) from the same cross. Transmission electron microscopy and DiI staining showed that the membrane structures of microspores and pollen in F1-D sterile hybrids were impaired. Carbol fuchsin staining revealed that cytomixis, chromosome loss and asymmetric callose wall formation occurred with high frequency in the microsporocytes and microspores of the sterile hybrids. The cytoplasm and nucleus were lost in the microspores and pollen of sterile hybrids, leading to mature pollen grains that were vacuous and collapsed in the aperture region. In addition, delayed tapetum degradation was detected in the anther of sterile hybrids, and sporopollenin was deposited in the aperture region. Impaired membrane structures of microspores and pollen in F1-D sterile hybrids affected the integrity of the cells, and might be associated with chromosome, nuclear and cytoplasm loss, vacuous pollen, and sterility in F1-D hybrids. Abnormal tapetum degradation in the anther and irregular sporopollenin deposition in the pollen wall of the F1-D sterile hybrids might also be related to the pollen sterility. This study deepens our understanding of the cytological mechanisms of hybrid sterility, and may facilitate the application of TSWV-resistant resources in cultivated Nicotiana species through hybrid fertility restoration and backcross breeding.

βVPE is involved in tapetal degradation and pollen development by activating proprotease maturation in Arabidopsis thaliana.

Vacuolar processing enzyme (VPE) is responsible for the maturation and activation of vacuolar proteins in plants. We found that βVPE was involved in tapetal degradation and pollen development by transforming proproteases into mature protease in Arabidopsis thaliana. βVPE was expressed specifically in the tapetum from stages 5 to 8 of anther development. The βVPE protein first appeared as a proenzyme and was transformed into the mature enzyme before stages 7-8. The recombinant βVPE protein self-cleaved and transformed into a 27 kDa mature protein at pH 5.2. The mature βVPE protein could induce the maturation of CEP1 in vitro. βvpe mutants exhibited delayed vacuolar degradation and decreased pollen fertility. The maturation of CEP1, RD19A, and RD19C was seriously inhibited in βvpe mutants. Our results indicate that βVPE is a crucial processing enzyme that directly participates in the maturation of cysteine proteases before vacuolar degradation, and is indirectly involved in pollen development and tapetal cell degradation.

Pollen development at high temperature and role of carbon and nitrogen metabolites.

Fruit and seed crop production heavily relies on successful stigma pollination, pollen tube growth, and fertilization of female gametes. These processes depend on production of viable pollen grains, a process sensitive to high-temperature stress. Therefore, rising global temperatures threaten worldwide crop production. Close observation of plant development shows that high-temperature stress causes morpho-anatomical changes in male reproductive tissues that contribute to reproductive failure. These changes include early tapetum degradation, anther indehiscence, and deformity of pollen grains, all of which are contributing factors to pollen fertility. At the molecular level, reactive oxygen species (ROS) accumulate when plants are subjected to high temperatures. ROS is a signalling molecule that can be beneficial or detrimental for plant cells depending on its balance with the endogenous cellular antioxidant system. Many metabolites have been linked with ROS over the years acting as direct scavengers or molecular stabilizers that promote antioxidant enzyme activity. This review highlights recent advances in research on anther and pollen development and how these might explain the aberrations seen during high-temperature stress; recent work on the role of nitrogen and carbon metabolites in anther and pollen development is discussed including their potential role at high temperature.

Ostkpr1 functions in anther cuticle development and pollen wall formation in rice

BackgroundDuring pollen wall formation in flowering plants, a conserved metabolon consisting of acyl-CoA synthetase (ACOS), polyketide synthase (PKS) and tetraketide α-pyrone reductase (TKPR), is required for sporopollenin synthesis. Despite this, the precise function of each of these components in different species remains unclear.ResultsIn this study, we characterized the function of OsTKPR1, a rice orthologue of Arabidopsis TKPR1. Loss of function of OsTKPR1 delayed tapetum degradation, reduced the levels of anther cuticular lipids, and impaired Ubisch body and pollen exine formation, resulting in complete male sterility. In addition, the phenylpropanoid pathway in mutant anthers was remarkably altered. Localization studies suggest that OsTKPR1 accumulates in the endoplasmic reticulum, while specific accumulation of OsTKPR1 mRNA in the anther tapetum and microspores is consistent with its function in anther and pollen wall development.ConclusionsOur results show that OsTKPR1 is indispensable for anther cuticle development and pollen wall formation in rice, providing new insights into the biochemical mechanisms of the conserved sporopollenin metabolon in flowering plants.