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Homeotic-like modification of stamens to petals is associated with aberrant mitochondrial gene expression in cytoplasmic male sterile Ogura Brassica juncea.

We have previously reported correction of severe leaf chlorosis in the cytoplasmic male sterile Ogura (also called Ogu) Brassica juncea line carrying Ogura cytoplasm by plastid substitution via protoplast fusion. Two cybrids obtained from the fusion experiment, Og1 and Og2, were green and carried the plastid genome of B. juncea cv. RLM198. While Og1 displayed normal flower morphology comparable to that of its euplasmic B. juncea counterpart except for sterile anthers, Og2 retained homeotic-like floral modification of stamens to petal-like structures and several other floral deformities observed in the chlorotic (Ogu) B. juncea cv. RLM198 (or OgRLM). With respect to the mitochondrial genome, Og1 showed 81% genetic similarity to the fertile cultivar RLM while Og2 showed 93% similarity to OgRLM. In spite of recombination and rearrangements in the mitochondrial genomes in the cybrids, expression patterns of 10 out of 11 mitochondrial genes were similar in all the three CMS lines; the only exception was atp6, whose expression was altered. While Og1 showed normal atp6 transcript similar to that in RLM, in Og2 and OgRLM weak expression of a longer transcript was detected. These results suggest that the homeotic-like changes in floral patterning leading to petaloid stamens in Og2 and OgRLM may be associated with aberrant mitochondrial gene expression.

Blotting, Northern↗

Analysis of MS2Bnap genomic DNA homologous to MS2 gene from Arabidopsis thaliana in two dominant digenic male sterile accessions of oilseed rape (Brassica napus L.).

PCR technique was employed to isolate gene homologous to the MS2Bnap (X99922.1) from two rapeseed (Brassica napus L.) dominant digenic male sterile lines, namely 220A (male sterile) and 220B (male fertile), 6A (male sterile) and 6C (male fertile). The isolated 2,581 bp sequences from 220A (named 220A-gDNA, GenBank accession number AY288778), 220B (220B-gDNA, AY257490), 6A (6A-gDNA, DQ060318) and 6C (6C-gDNA, DQ060319) all contained six introns. Forty-one single nucleotide polymorphism (SNP) sites were detected by alignment of these four sequences, seven of them dispersed in the exon regions. Two SNPs (1247, 1656) were detected between 220A-gDNA and 220B-gDNA, and the one at nucleotide 1247 of 220A-gDNA with A replaced by C was a missense mutation, which may be the putative male sterility site in 220A. All eight SNPs identified between 6A-gDNA and 6C-gDNA were located in the third intron, so the proteins encoded by them are the same. The one SNP between 6A-/6C-gDNA and 220A-/220B-gDNA at nucleotide 2474 of 220A-/220B-gDNA with C replaced by G was a missense mutation. Mutation site of BNMS2PROT (CAA68190.1) encoded by MS2Bnap in 220A(254) and 6A/6C(584) is different, which indicated dominant digenic male sterile line 220AB and 6CA have some difference in the molecular level. Comparison of structure of MS2Bnap in B. napus with that of MS2 in Arabidopsis thaliana revealed that the similarity of exons between these two genes is higher than that of introns.

Amino Acid Sequence↗

The organization of mitochondrial atp6 gene region in male fertile and CMS lines of pepper (Capsicum annuum L.).

The mitochondrial atp6 gene in male fertile (N) and CMS (S) pepper has previously been compared and was found to be present in two copies (Kim et al. in J Kor Soc Hort Sci 42:121-127 2001). In the current study, these atp6 copies were amplified by an inverse PCR technique, and the coding region as well as the 5' and 3' flanking regions were sequenced. The atp6 copies in CMS pepper were detected as one intact gene and one pseudogene, truncated at the 3' coding region. When the atp6 genes in pepper were compared to other plant species, pepper, potato, and petunia all possessed a sequence of 12 identical amino acids at the 3' extended region, which was considered a hallmark of the Solanaceae family. Northern blot analysis showed differences in mRNA band patterns between CMS and restorer lines, indicating that atp6 gene is one of the candidates for CMS in pepper.

Amino Acid Sequence↗

Improved Agrobacterium-mediated transformation of three maize inbred lines using MS salts.

Transformation technology as a research or breeding tool to improve maize is routinely used in most industrial and some specialized public laboratories. However, transformation of many inbred lines remains a challenging task, especially when using Agrobacterium tumefaciens as the delivery method. Here we report success in generating transgenic plants and progeny from three maize inbred lines using an Agrobacterium-mediated standard binary vector system to target maize immature embryos. Eleven maize inbred lines were pre-screened for transformation frequency using N6 salts. A subset of three maize inbred lines was then systematically evaluated for frequency of post-infection embryogenic callus induction and transformation on four media regimes: N6 or MS salts in each of two distinct media backgrounds. Transgenic plants recovered from inbred lines B104, B114, and Ky21 were analyzed for transgene integration, expression, and transmission. Average transformation frequencies of 6.4% (for B104), 2.8% (for B114), and 8% (for Ky21) were achieved using MS salts. Availability of Agrobacterium-mediated maize inbred line transformation will improve future opportunities for maize genetic and functional genomic studies.

Blotting, Southern↗

Bisexual sterility conferred by the differential expression of barnase and barstar: a simple and efficient method of transgene containment.

To establish a simple and an efficient system to minimize the environmental risk of genetically modified plants, we tested the applicability of the barnase/barstar system in conferring bisexual sterility; that is, in preventing plants setting seeds by self-fertilization and out-crossing. Transgenic tobacco plants were generated to express barnase, a cell death inducing ribonuclease, under the control of the gamete-specific AtDMC1 promoter, and barstar, a specific inhibitor of barnase, under the control of the ACT2 promoter, which is constitutively active in almost all tissues except gametes. In contrast to control plants harboring the barstar expression unit only, which set seeds normally with self-pollination, all transformants harboring both barnase and barstar were bisexually sterile. They produced aberrant anthers containing no detectable pollen and failed to set seeds even after pollination with wild-type tobacco pollen.

Arabidopsis↗

Cytological mechanism of pollen abortion resulting from allelic interaction of F1 pollen sterility locus in rice (Oryza sativa L.).

Pollen abortion is one of the major reasons causing the inter-subspecific F(1) hybrid sterility in rice and is due to allelic interaction of F(1) pollen sterility genes. The microsporogenesis and microgametogenesis of Taichung 65 and its three F(1) hybrids were comparatively studied by using techniques of differential interference contrast microscopy, semi-thin section light microscopy, epifluorescence microscopy and TEM. The results showed that there were differences among the cytological mechanisms of pollen abortion due to allelic interaction at the three F(1) pollen sterility loci. The allelic interaction at S-a locus resulted in microspores unable to extend the protoplasm membrane with the enlargement of the microspore at the middle microspore stage and finally producing empty abortive pollen. The allelic interaction at S-b locus caused asynchronous development of microspores at the middle microspore stage producing stainable abortive pollen. The allelic interaction at S-c locus mainly led to the non-dissolution of the generative cell wall and finally caused the hybrid F(1) mainly producing stainable abortive pollen. Genotypic identification indicated that the abortive pollen were those with S ( j ) allele.

Alleles↗

The rice OsRad21-4, an orthologue of yeast Rec8 protein, is required for efficient meiosis.

In yeast, Rad21/Scc1 and its meiotic variant Rec8 are key players in the establishment and subsequent dissolution of sister chromatid cohesion for mitosis and meiosis, respectively, which are essential for chromosome segregation. Unlike yeast, our identification revealed that the rice genome has 4 RAD21-like genes that share lower than 21% identity at polypeptide levels, and each is present as a single copy in this genome. Here we describe our analysis of the function of OsRAD21-4 by RNAi. Western blot analyses indicated that the protein was most abundant in young flowers and less in leaves and buds but absent in roots. In flowers, the expression was further defined to premeiotic pollen mother cells (PMCs) and meiotic PMCs of anthers. Meiotic chromosome behaviors were monitored from male meiocytes of OsRAD21-4-deficient lines mediated by RNAi. The male meiocytes showed multiple aberrant events at meiotic prophase I, including over-condensation of chromosomes, precocious segregation of homologues and chromosome fragmentation. Fluorescence in situ hybridization experiments revealed that the deficient lines were defective in homologous pairing and cohesion at sister chromatid arms. These defects resulted in unequal chromosome segregation and aberrant spore generation. These observations suggest that OsRad21-4 is essential for efficient meiosis.

Amino Acid Sequence↗

Biochemical and functional characterization of ORF138, a mitochondrial protein responsible for Ogura cytoplasmic male sterility in Brassiceae.

In cytoplasmic male sterility (CMS), original mitochondrial genes contribute to sex determinism by provoking pollen abortion. The function of the encoded proteins remains unclear. We studied the ORF138 protein, responsible for the 'Ogura' CMS, which is both used in hybrid seed production and present in natural populations. We analyzed the biochemical and structural properties of this protein in male-sterile plants and in E. coli. We showed that this protein spontaneously forms dimers in vitro. Truncated variants of the protein, containing either the hydrophobic or the hydrophilic moiety, also spontaneously dimerize. By fractionating mitochondria, we showed that ORF138 was strongly associated with the inner mitochondrial membrane of male-sterile plants. Our results also strongly suggest that ORF138 forms oligomers in male-sterile plant mitochondria. In E. coli, ORF138 was associated with the plasma membrane, as shown by membrane fractionation, and formed oligomers. The production of this protein strongly inhibited bacterial growth, but not by inhibiting respiration. The observed toxic effects required both the hydrophilic and hydrophobic moieties of the protein.

Base Sequence↗

The molecular biology of cytoplasmically inherited male sterility and prospects for its engineering.

Nucleocytoplasmic male sterilities are binary genetic systems driven by mitochondrial, maternally inherited genes that induce male sterility and a female phenotype and which are overcome by nuclear restorers of fertility. They contribute to the reproductive biology and evolution of natural populations and are valuable tools for the commercial production of hybrid seeds in crops. For species with no natural form of cytoplasmic male sterility, such sterility can in some cases be introduced from different, but related, species through sexual crosses or somatic hybridisation. Somatic hybridisation is the only technique currently available for manipulating plant mitochondrial genomes. Recent successes in plastid transformation have opened up entirely new perspectives for the engineering of cytoplasmic male sterilities in transplastomic plants.

Cell Nucleus↗

Cytoplasmic male sterility: a window to the world of plant mitochondrial-nuclear interactions.

Mitochondrial function depends on the coordinate action of nuclear and mitochondrial genomes. The genetic dissection of these interactions presents special challenges in obligate aerobes, because the viability of these organisms depends on mitochondrial respiration. The plant trait cytoplasmic male sterility (CMS) is determined by the mitochondrial genome and is associated with a pollen sterility phenotype that can be suppressed or counteracted by nuclear genes known as restorer-of-fertility genes. Here, I review the nature and the origin of the genes that determine CMS, together with recent investigations that have exploited CMS to provide new insights into plant mitochondrial-nuclear communication. These studies have implicated mitochondrial signaling pathways, including those involved in regulating cell death and nuclear gene expression, in the elaboration of CMS. The molecular cloning of nuclear genes that restore fertility (i.e. restorer-of-fertility genes) has identified genes encoding pentatricopeptide-repeat proteins as key regulators of plant mitochondrial gene expression.

Cell Nucleus↗

Alternatively spliced killer-protector system confers S19-mediated hybrid male sterility in rice.

Hybrid sterility limits the use of strong interspecific heterosis and S19 is a major locus that confers hybrid sterility between Oryza sativa (Asian cultivated rice) and Oryza glaberrima (African cultivated rice). However, the S19 is not yet cloned and its underlying mechanism remains elusive. In this study, we identify two closely linked genes (S19A1 and S19A7) specific to African rice allele that encode a killer-protector module at the S19 locus. Two alternatively spliced transcripts expressed from the killer gene S19A1 (S19A1.1 and S19A1.2) encode mitochondria-targeted cytotoxic proteins that cause toxicity diversity for somatic and/or gametic cell death, respectively. However, S19A7 interacts with S19A1.1 and S19A1.2, blocking their cytotoxic effect. Because the Asian rice S19 allele lacks S19A1 and S19A7, male gametes that carry this allele are selectively aborted in Asian-African F1 hybrids. Knockout of S19A1 can overcome S19-mediated hybrid sterility. Haplotype analysis reveals that the functional S19 allele is absent in non-AA-genome Oryza species and likely emerged in the O. barthii-O. glaberrima lineage through a multi-step evolutionary process. Our findings provide insight into the genetic mechanisms responsible for hybrid sterility between Asian and African rice and suggest genetic and biotechnological strategies for the use of interspecific heterosis in rice.

Oryza↗

Low temperature treatment at the young microspore stage induces protein changes in rice anthers.

Male reproductive development in rice is very sensitive to various forms of environmental stresses including low temperature. A few days of cold treatment (<20 degrees C) at the young microspore stage induce severe pollen sterility and thus large grain yield reductions. To investigate this phenomenon, anther proteins at the early stages of microspore development, with or without cold treatment at 12 degrees C, were extracted, separated by two-dimensional gel electrophoresis, and compared. The cold-sensitive cultivar Doongara and the relatively cold-tolerant cultivar HSC55 were used. The abundance of 37 anther proteins was changed more than 2-fold after 1, 2, and 4 days of cold treatment in cv. Doongara. Among them, one protein was newly induced, 32 protein spots were up-regulated, and four protein spots were down-regulated. Of these 37 protein spots, we identified two anther-specific proteins (putative lipid transfer protein and Osg6B) and a calreticulin that were down-regulated and a cystine synthase, a beta-6 subunit of the 20 S proteasome, an H protein of the glycine cleavage system, cytochrome c oxidase subunit VB, an osmotin protein homologue, a putative 6-phosphogluconolactonase, a putative adenylate kinase, a putative cysteine proteinase inhibitor, ribosomal protein S12E, a caffeoyl-CoA O-methyltransferase, and a monodehydroascorbate reductase that were up-regulated. Identification of these proteins is available upon request. Accumulation of these proteins did not vary greatly after cold treatment in panicles of cv. Doongara or in the anthers of the cv. HSC55. The newly induced protein named Oryza sativa cold-induced anther protein (OsCIA) was identified as an unknown protein. The OsCIA protein was detected in panicles, leaves, and seedling tissues under normal growth conditions. Quantitative real time RT-PCR analysis of OsCIA mRNA expression showed no significant change between low temperature-treated and untreated plants. A possible regulatory role for the newly induced protein is proposed.

Amino Acid Sequence↗

The male sterility-associated pcf gene and the normal atp9-1 gene in Petunia are located on different mitochondrial DNA molecules.

A mitochondrial DNA (mtDNA) region termed the S-pcf locus has previously been correlated with cytoplasmic male sterility (CMS) in Petunia. In order to understand the relationship of the S-pcf locus to homologous sequences found elsewhere in mtDNAs of both CMS and fertile lines, the structure of the mitochondrial genome of CMS Petunia line 3688 was determined by cosmid walking. The S-pcf locus, which includes the only copies of genes for NADH dehydrogenase subunit 3 (nad3) and small ribosomal subunit protein 12 (rps12) was found to be located on a circular map of 396 kb, while a second almost identical circular map of 407 kb carries the only copies of the genes for 18S and 5S rRNA (rrn18 and rrn5), the only copy of a conserved unidentified gene (orf25), and the only known functional copy of atp9. Three different copies of a recombination repeat were found in six genomic environments, predicting sub-genomic circles of 277, 266 and 130 kb. The ratio of atp9 to S-pcf mtDNA sequences was approximately 1.5 to 1, indicating that sub-genomic molecules carrying these genes differ in abundance. Comparison of the mtDNA organization of the CMS line with that of the master circle of fertile Petunia line 3704 reveals numerous changes in order and orientation of ten different sectors.

Blotting, Southern↗

MSH2 is essential for the preservation of genome integrity and prevents homeologous recombination in the moss Physcomitrella patens.

MSH2 is a central component of the mismatch repair pathway that targets mismatches arising during DNA replication, homologous recombination (HR) and in response to genotoxic stresses. Here, we describe the function of MSH2 in the moss Physcomitrella patens, as deciphered by the analysis of loss of function mutants. Ppmsh2 mutants display pleiotropic growth and developmental defects, which reflect genomic instability. Based on loss of function of the APT gene, we estimated this mutator phenotype to be at least 130 times higher in the mutants than in wild type. We also found that MSH2 is involved in some but not all the moss responses to genotoxic stresses we tested. Indeed, the Ppmsh2 mutants were more tolerant to cisplatin and show higher sensitivity to UV-B radiations. PpMSH2 gene involvement in HR was studied by assessing gene targeting (GT) efficiency with homologous and homeologous sequences. GT efficiency with homologous sequences was slightly decreased in the Ppmsh2 mutant compared with wild type. Strikingly GT efficiency with homeologous sequences decreased proportionally to sequence divergence in the wild type whereas it remained unaffected in the mutants. Those results demonstrate the role of PpMSH2 in the maintenance of genome integrity and in homologous and homeologous recombination.

Bryopsida↗

An alloplasmic male-sterile line of Brassica oleracea harboring the mitochondria from Diplotaxis muralis expresses a novel chimeric open reading frame, orf72.

Nuclear so-called fertility-restorer genes reverse the pollen sterility of cytoplasmic male-sterile (CMS) plants caused by disturbed mitochondrial-nuclear interactions. We identified a CMS-associated chimeric mitochondrial gene in an alloplasmic CMS line of Brassica oleracea in the 'mur' system. This novel chimeric gene, orf72, was found in the mitochondrial genome of donor cytoplasm. It was located downstream of normal rps7 and contained part of atp9 (atp9-b). It was expressed specifically on the nuclear background of CMS B. oleracea, partially suppressed in the fertility-restored line and entirely suppressed in the cytoplasmic donor.

Amino Acid Sequence↗

Glyphosate-induced anther indehiscence in cotton is partially temperature dependent and involves cytoskeleton and secondary wall modifications and auxin accumulation.

Yield reduction caused by late application of glyphosate to glyphosate-resistant cotton (Gossypium hirsutum; GRC) expressing CP4 5-enol-pyruvylshikmate-3-P synthase under the cauliflower mosaic virus-35S promoter has been attributed to male sterility. This study was aimed to elucidate the factors and mechanisms involved in this phenomenon. Western and tissue-print blots demonstrated a reduced expression of the transgene in anthers of GRC compared to ovules of the same plants. Glyphosate application to GRC grown at a high temperature regime after the initiation of flower buds caused a complete loss of pollen viability and inhibition of anther dehiscence, while at a moderate temperature regime only 50% of the pollen grains were disrupted and anther dehiscence was normal. Glyphosate-damaged anthers exhibited a change in the deposition of the secondary cell wall thickenings (SWT) in the endothecium cells, from the normal longitudinal orientation to a transverse orientation, and hindered septum disintegration. These changes occurred only at the high temperature regime. The reorientation of SWT in GRC was accompanied by a similar change in microtubule orientation. A similar reorientation of microtubules was also observed in Arabidopsis (Arabidopsis thaliana) seedlings expressing green fluorescent protein tubulin (tubulin alpha 6) following glyphosate treatment. Glyphosate treatment induced the accumulation of high levels of indole-3-acetic acid in GRC anthers. Cotton plants treated with 2,4-dichlorophenoxyacetic acid had male sterile flowers, with SWT abnormalities in the endothecium layer similar to those observed in glyphosate-treated plants. Our data demonstrate that glyphosate inhibits anther dehiscence by inducing changes in the microtubule and cell wall organization in the endothecium cells, which are mediated by auxin.

2,4-Dichlorophenoxyacetic Acid↗

Mutations in Arabidopsis yellow stripe-like1 and yellow stripe-like3 reveal their roles in metal ion homeostasis and loading of metal ions in seeds.

Here, we describe two members of the Arabidopsis (Arabidopsis thaliana) Yellow Stripe-Like (YSL) family, AtYSL1 and AtYSL3. The YSL1 and YSL3 proteins are members of the oligopeptide transporter family and are predicted to be integral membrane proteins. YSL1 and YSL3 are similar to the maize (Zea mays) YS1 phytosiderophore transporter (ZmYS1) and the AtYSL2 iron (Fe)-nicotianamine transporter, and are predicted to transport metal-nicotianamine complexes into cells. YSL1 and YSL3 mRNAs are expressed in both root and shoot tissues, and both are regulated in response to the Fe status of the plant. Beta-glucuronidase reporter expression, driven by YSL1 and YSL3 promoters, reveals expression patterns of the genes in roots, leaves, and flowers. Expression was highest in senescing rosette leaves and cauline leaves. Whereas the single mutants ysl1 and ysl3 had no visible phenotypes, the ysl1ysl3 double mutant exhibited Fe deficiency symptoms, such as interveinal chlorosis. Leaf Fe concentrations are decreased in the double mutant, whereas manganese, zinc, and especially copper concentrations are elevated. In seeds of double-mutant plants, the concentrations of Fe, zinc, and copper are low. Mobilization of metals from leaves during senescence is impaired in the double mutant. In addition, the double mutant has reduced fertility due to defective anther and embryo development. The proposed physiological roles for YSL1 and YSL3 are in delivery of metal micronutrients to and from vascular tissues.

Arabidopsis↗

Rice Undeveloped Tapetum1 is a major regulator of early tapetum development.

The tapetum, the innermost of four sporophytic layers in the anther wall, comes in direct contact with the developing male gametophyte and is thought to play a crucial role in the development and maturation of microspores. Here, we report the identification of rice (Oryza sativa) Undeveloped Tapetum1 (Udt1), which is required for the differentiation of secondary parietal cells to mature tapetal cells. T-DNA or retrotransposon Tos17 insertions in the Udt1 gene caused male sterility. The anther walls and meiocytes of the mutants were normal during the early premeiosis stage, but their tapeta failed to differentiate and became vacuolated during the meiotic stage. In addition, meiocytes did not develop to microspores, and middle layer degeneration was inhibited. Consequently, the anther locules contained no pollen. The UDT1:green fluorescent protein fusion protein was localized to the nucleus. This, together with its homology with other basic helix-loop-helix proteins, suggests that UDT1 is a transcription factor. DNA microarray analysis identified 958 downregulated and 267 upregulated genes in the udt1-1 anthers, suggesting that Udt1 plays a major role in maintaining tapetum development, starting in early meiosis.

Basic Helix-Loop-Helix Leucine Zipper Transcriptio↗