Instability of s male-sterile cytoplasm in maize

A number of S male-sterile plants from several shrunken-2 inbred lines were crossed initially with an R138-TR inbred line pollinator carrying the nonrestoring genotype for S sterile cytoplasm. One such cross, involving a male-sterile female parent from inbred line M825, produced, unexpectedly, a number of male-fertile F₁ progeny, along with the expected male-sterile off-spring. Pollen records of plants in F₂, F₃ and F₄ progenies in the exceptional pedigree, and of a variety of testcross and backcross progenies from these male-fertile exceptions, indicate that the exceptional male fertility is not attributable to the action of either dominant or recessive nuclear restorer genes. They are, however, consistent with the hypothesis that the event responsible for the appearance of exceptional male-fertile offspring among progeny of the original cross involved a change from male-sterile to male-fertile condition in the cytoplasm of the male-sterile M825 plant involved as the female parent in this cross. It appears that this plant bore an ear in which there was a relatively early mutational event at the cytoplasmic level resulting in a chimera involving some kernels which carried S male-sterile cytoplasm, and others which carried the mutated fertile cytoplasmic condition. The finding of a number of additional ear chimeras supports this contention.—The evidence suggests that the change from sterile to fertile cytoplasm has occurred in a number of other instances. The male-sterile line M825 is especially prone to this change. These findings are of particular interest because it has heretofore been considered that both S and T types of male-sterile cytoplasm are highly stable.—The data presented here are not sufficient to support the notion that the exceptional event involves a qualitative change, analogous to gene mutation, in a cytoplasmic entity governing the expression of male fertility. It is equally plausible that the exceptional male fertility is the result of occasional transfer of normal cytoplasm through the male germ cells of maintainer parents.     

A CMS-Related Gene, Ψatp6-2, Causes Increased ATP Hydrolysis Activity of the Mitochondrial F1Fo-ATP Synthase and Induces Male Sterility in Pepper (Capsicum annuum L.)

Pollen formation is a complex process that is strictly controlled by genetic factors. Although many novel mitochondrial genes have been implicated in the dysfunction of mitochondrial enzymes and the cytoplasmic male sterility (CMS), there is little empirical evidence to show that CMS-related genes actually result in the dysfunction of enzyme and little is known about the regulatory mechanisms of the aberrant mitochondrial enzymes in male sterility in CMS lines. Here, we report the characterization of a novel mitochondrial gene, Ψatp6-2, which is hypothesized to play a role in male sterility in pepper. Using virus-induced gene silencing (VIGS), we observed that silencing the atp6-2 gene in the maintainer line resulted in an increase in ATP hydrolysis activity of the mitochondrial F₁F_o-ATP synthase along with pollen abortion, while silencing the truncated Ψatp6-2 gene in the CMS line resulted in an inhibition of ATP hydrolysis activity and restoration of fertility. Altered ATP hydrolysis also affected the tolerance of the gene-silenced plants to abiotic stresses. Localization experiments showed that premature ATP hydrolysis occurred at the tetrad stage of pollen development in the CMS line, but no ATPase activity was observed in the microspores at the later stage. These results suggest that the Ψatp6-2 gene causes the alteration in ATP hydrolysis activity of the mitochondrial F₁F_o-ATP synthase during pollen development, which eventually leads to male sterility in pepper.     

Identification of a single nucleotide deletion causing frameshift mutation in OsDFR2A in a genic male sterile mutant of rice and its possible application to F1 hybrid breeding

Stable genic male sterility (GMS), which is not influenced by environmental factors, has not been used for F₁ hybrid seed production because male-sterile inbred lines cannot be developed and male-sterile plants must be selected from segregating populations every time. However, the stability of male sterility may provide a reliable system for F₁ seed production without contamination of selfed seeds. A genic male-sterile mutant in rice (Oryza sativa L.), C204, which was selected from progeny of the cultivar ‘Koshihikari’ irradiated by gamma rays, has shorter and whiter anthers than those of ‘Koshihikari’ and has no pollen grains. Segregation analysis of C204 suggested the male sterility of this mutant to be controlled by a recessive allele of a single gene. Linkage analysis of a mutated gene responsible for the male sterility revealed the gene to be in a region of ca. 75 kb on the long arm of chromosome 9. The nine genes predicted in the 75-kb region were sequenced, and compared with the published Nipponbare genome sequences. A single-base deletion was found in the first exon of a C204 allele of Os09g0493500, which encodes an NAD-dependent epimerase/dehydratase family protein, resulting in a frameshift causing a premature stop codon. A dot-blot single nucleotide polymorphism marker for detection of the single-base deletion in Os09g0493500 was developed. We herein propose an F₁ hybrid seed production system using stable GMS with a simple selection method of GMS plants.     

Mitochondrial DNA variation in maize plants regenerated during tissue culture selection

Summary Plants resistant to Helminthosporium maydis race T were obtained following selection for H. maydis pathotoxin resistance in tissue cultures of susceptible, Texas male-sterile (T) cytoplasm maize. The selected lines transmitted H. maydis resistance to their sexual progeny as an extranuclear trait. Of 167 resistant, regenerated plants, 97 were male fertile and 70 were classified male sterile for reasons that included abnormal plant, tassel, anther or pollen development. No progeny were obtained from these male-sterile, resistant plants. Male fertility and resistance to the Phyllosticta maydis pathotoxin that specifically affects T cytoplasm maize were co-transmitted with H. maydis resistance to progeny of male-fertile, resistant plants. These three traits previously were associated only with the normal (N) male-fertile cytoplasm condition in maize. Three generations of progeny testing provided no indication that the cytoplasmic association of male sterility and toxin susceptibility had been broken by this selection and regeneration procedure. Restriction endonuclease analysis of mitochondrial DNA (mtDNA) revealed that three selected, resistant lines had distinct mtDNA organization that distinguished them from each other, from T and from N cytoplasm maize. Restriction patterns of the selected resistant lines were similar to those from T cytoplasm mtDNA; these patterns had not been observed in any previous analyses of various sources of T cytoplasm. The mtDNA analyses indicated that the male-fertile, toxin-resistant lines did not originate from selection of N mitochondrial genomes coexisting previously with T genomes in the T cytoplasm line used for selection.Scientific Journal Series Article no. 11,185 of the Minnesota Agricultural Experiment Station and no. 2295 of the Florida Agricultural Experiment Station. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee of warrantly of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable     

The restoration of male fertility in F1 wheat hybrids

The yield of F₁ wheat hybrids is often limited by reduced male fertility. Improvement depends upon selecting male and female parents capable of allowing good fertility ‘restoration’ in the F₁ hybrids. Assessment of restoring potential in growth rooms was difficult because fertility was much lower than in field grown plants. In the field, two experiments showed differences between parent lines but also that the fertilities of the F₁ hybrids were site-specific, and that this factor might be considered during further selection. Variation between reciprocal crosses, possibly due to cytoplasmic differences, rendered a proposed test for the early assessment of fertility restoration capacity amongst potential male-sterile lines to be of doubtful value with present stocks.     

FLP-mediated recombination for use in hybrid plant production

We have studied the feasibility in Arabidopsis of using a site-specific recombination system FLP/FRT, from the 2 microm plasmid of yeast, for making plant hybrids. Initially, Arabidopsis plants expressing the FLP site-specific recombinase were crossed with plants transformed with a vector containing kanamycin-resistance gene (npt) flanked by FRT sites, which also served to separate the CaMV35S promoter from a promoterless gusA. Hybrid progeny were tested for excision of the npt gene and the positioning of 35S promoter proximal to gusA. GUS activity was observed in the progeny of all crosses, but not in the progeny derived from the self-pollinated homozygous parents. We then induced male sterility in Arabidopsis plants using the antisense expression of a pollen- and tapetum-specific gene, bcp1, flanked by FRT sites. Upon cross-pollination of flowers on the same male-sterile plants with pollen from FLP-containing plants, viable seeds were produced and the progeny hybrid plants developed normally. Molecular analyses revealed that the antisense expression cassette of bcp1 had been excised in these plants. These results show for the first time that a site-specific recombinase can be used to restore fertility in male-sterile plants, providing an alternative method for the production of hybrid seeds and plants.     

Loss of CMS-specific mitochondrial DNA arrangement in fertile segregants of Petunia hybrids

The progeny of somatic hybrid Petunia plants derived from the fusion of a male-fertile line and a cytoplasmic male-sterile (cms) line were examined. Male-fertile progeny derived from three different male-sterile somatic hybrid plants did not exhibit the mitochondrial DNA (mtDNA) arrangement which has previously been correlated with cms in Petunia. The cms-associated mtDNA arrangement was present in the male-sterile predecessors of these fertile revertants. Thus, it is concluded that the loss of this mtDNA arrangement is associated with reversion to fertility in the progeny of the unstable somatic hybrid petunia plants.     

Cytoplasmic male sterility and nuclear restorer genes in a natural population of Beta maritima: genetical and molecular aspects

Summary One natural population (F₀ generation) of Beta maritima situated on the French Atlantic coast has been analysed. It was composed of 62% female, 30% hermaphrodite and 8% intermediate plants. The analysis of half-sib progeny (F₁ generation) obtained from in situ open pollination demonstrates the cytoplasmic determination of male sterility in Beta maritima and the restoration of fertility by nuclear genes. The mitochondrial DNA (mtDNA) and the chloroplast DNA (ctDNA) of sixteen F₁ plants, extracted from offspring of the three sexual phenotypes, were analysed using the restriction enzymes Sal I and Bam HI, respectively. Two cytoplasmic lines with their own peculiar genetic characteristics were distinguished using the restriction enzyme patterns of mtDNA: (i) the S cytoplasmic line was found in segregating progeny of two F₀ plants; all three phenotypes were produced (that is, progeny including hermaphrodite, female and intermediate plants); (ii) the N cytoplasmic line was found in the progeny of one F₀ hermaphrodite plant; this produced only hermaphrodites. Thus, segregating and non-segregating hermaphrodite F₀ plants can be distinguished. The nuclear genes maintaining sterility or restoring fertility are expressed in line S. At the same time the analysis of Beta vulgaris material has been carried out at the molecular level: N cytoplasmic lines of B. vulgaris and B. maritima differed only by 3 fragments of mtDNA; but the S cytoplasmic line of B. maritima was very different from Owen's cytoplasmic male sterile line of B. vulgaris. No variation in the ctDNA pattern was detected within and between the two taxa.     

Genetics and ultrastructure of a cytoplasmically inherited yellow mutant in soybeans

A chimeric plant was observed in the F₂ generation of a cross between a male-sterile line and a plant introduction homozygous for a chromosome interchange in soybeans [Glycine max (L.) Merr.]. F₃ progeny of this plant included one chimera, 36 yellow plants and 16 green plants. The yellow plants, which progressively turn green, were viable and fertile in field, greenhouse and growth-chamber environments. Reciprocal cross-pollinations were made between these yellow plants and four known nuclear yellow mutant plants, between these yellow plants and sibling green plants and between these yellow plants and unrelated green plants. Segregation data from F₁ and F₂ generations indicated cytoplasmic inheritance of the newly discovered yellow phenotype. Pollinations in which reciprocal F₁ hybrid plants were used as male or female parents were made with unrelated green plants. Observations in F₁ and F₂ generations substantiated the hypothesis of cytoplasmic inheritance. No interactions have been observed between this mutant and the various nuclear backgrounds. This is the first report of a cytoplasmically inherited mutant affecting plant color in soybeans. Exchange grafts were made between cytoplasmic yellow plants and sibling green plants and between cytoplasmic yellow plants and unrelated green plants. The phenotype was controlled by the scion, indicating that graft-transmissible agents were not involved. When grown in darkness, cytoplasmic yellow plants and normal green plants accumulated the same amount of protochlorophyllide. Cytoplasmic yellow plants grown in dim light accumulated slightly less chlorophyll than did their green siblings. Electron photomicrographs showed that the prolamellar body (a structure associated with synthesis of protochlorophyllide) and chloroplast ultrastructure were normal in the cytoplasmic yellow mutant. These observations led to the hypothesis that the synchrony involved in deposition of nuclear and cytoplasmic gene products during organelle development is impaired in this cytoplasmic mutant.     

与烟草细胞质雄性不育相关的线粒体基因atp9的mRNA研究

已知导入未编辑atp9 mRNA的烟草表现细胞质雄性不育(CMS),因此认为线粒体基因atp9是引起高等植物CMS的主要基因。为了解atp9在CMS中的作用机制,从3对烟草不育系及其同型保持系中提取atp9,利用实验与理论结合来分析其mRNA在编辑前后以及在不育系及其同型保持系中的一维、三维信息差别。结果表明,atp9mRNA一维信息方面的差异,更重要的是二级结构的差异和稳定性,可能是影响ATP合成而导致CMS的根本原因。