Photoperiod-sensitive Cytoplasmic Male Sterility Research Articles

Hybrid wheat breeding using photoperiod-sensitive cytoplasmic male sterility (PCMS) caused by <i>Aegilops crassa</i> cytoplasm

Hybrid wheat breeding using photoperiod-sensitive cytoplasmic male sterility (PCMS) caused by <i>Aegilops crassa</i> cytoplasm

Chemically induced male sterility in common wheat mediated by Aegilops cytoplasm

Several approaches have been proposed, in the past, for the development of hybrid wheat varieties. Nevertheless, common wheat hybrids today account for less than 1% of the world's wheat production. The reason for the limited success of hybrid wheat varieties is the fact that to date, a simple and efficient system for the production of hybrid seed has not been developed. A two-line system using photoperiod-sensitive cytoplasmic male sterility (PCMS) caused by Aegilops crassa Boiss. cytoplasm seems to be very promising way to produce hybrid wheat seed on large scale. Non-desirable side effects of PCMS system are the unreliable sterility of the male sterile lines under different latitudes. Therefore, we tried to connect male sterility system based on Ae. crassa cytoplasm with chemical induction of male sterility. The presented results reveal that the majority of male sterility genes are conserved in the Ae. crassa cytoplasm and that their effects can be promoted by chemical signals, such as synthetic auxins (e.g., 2,4-Dichlorophenoxyacetic acid). Our research work represents the development of a novel male sterility system which is controlled by chemical signals (e.g., synthetic auxins and their pro-herbicide analogues) and mediated by Ae. crassa cytoplasm.

Development of photoperiod-sensitive cytoplasmic male sterile (PCMS) wheat lines showing high male sterility under long-day conditions and high seed fertility under short-day conditions

A “two-line system” using photoperiod-sensitive cytoplasmic male sterility (PCMS) caused by Aegilops crassa cytoplasm under long-day photoperiods (≧15 h) has been proposed as a means of producing hybrid varieties in common wheat (Triticum aestivum). The PCMS line is maintained by self-pollination under short-day conditions, and hybrid seeds can be produced through outcrossing of the PCMS line with a pollinator line under long-day conditions. Our previous studies revealed that PCMS lines showing complete male sterility under long-day conditions are necessary for practical hybrid wheat breeding, especially to obtain high hybrid purity in F1 seeds. Furthermore, practical PCMS lines should have high seed fertility under short-day conditions, which is associated with female fertility. Wheat cv. Norin 26 with Ae. crassa cytoplasm exhibits high seed fertility under short-day conditions, and cv. Fujimikomugi with Ae. crassa cytoplasm shows high male sterility under long-day conditions. Here we developed practical PCMS lines derived from the F1 generation of Norin 26 and Fujimikomugi (with Ae. crassa cytoplasm) that were then backcrossed to elite wheat lines.

Comparison of two fertility restoration systems against photoperiod‐sensitive cytoplasmic male sterility in wheat

AbstractA ‘two‐line system’ using photoperiod‐sensitive cytoplasmic male sterility (PCMS) caused by Aegilops crassa cytoplasm under a long‐day photoperiod ( 15 h) has been proposed as a new means of producing hybrid varieties in common wheat. The PCMS line is maintained by self‐pollination under short‐day conditions, and hybrid seeds can be produced through outcrossing of the PCMS line with a pollinator under long‐day conditions. Two kinds of fertility restoration systems against the PCMS are known. One is involved with a set of multiple fertility‐restoring (Rf) genes in the wheat cultivar ‘Norin 61’ located on (at least) chromosomes 4A, 1D, 3D and 5D. The other is controlled by a single dominant major Rf gene, Rfd1, located on the long arm of chromosome 7B in the wheat cultivar ‘Chinese Spring’. To examine the degree of fertility restoration by these two systems, nine PCMS lines were crossed with ‘Norin 61’ and ‘Chinese Spring’ as the restorer lines, and the F1 hybrids were investigated. The degree of fertility restoration was estimated by comparing the seed set rates in the F1 hybrids having the Ae. crassa cytoplasm and those with normal cytoplasm. The results revealed that the fertility restoration ability of a set of multiple Rf genes in ‘Norin 61’ was higher than that of the Rfd1 gene in ‘Chinese Spring’.

Factors responsible for levels of male sterility in photoperiod-sensitive cytoplasmic male sterile (PCMS) wheat lines

A `two-line system' using photoperiod-sensitivecytoplasmic male sterility (PCMS) caused by Aegilops crassa cytoplasm has been proposed as a newmeans of producing hybrid wheat. The PCMS line ismaintained by self-pollination under short-dayconditions (≦14.5 h light period), and F1 seedscan be produced by outcrossing of the PCMS line witha pollinator under long-day conditions (≧15 h lightperiod). As the levels of male sterility in PCMSlines under the long-day conditions is a crucialfactor in determining hybrid purity of the F1seeds, a study was conducted into the effect ofseeding rate on male sterility in PCMS lines. Threedifferent density levels were tested using analloplasmic line of Japanese wheat cultivar `Norin 26'which exhibits PCMS. Levels of male sterility of thePCMS line increased at sparse planting, because tiller(ear) number per plant increased at low seedingdensity and late-appearing ears tended to exhibithigher levels of male sterility than early-appearingears. On the other hand, male sterility levels of thePCMS lines depended on genotype, e.g., the PCMS`Fujimikomugi' was completely male sterile, whereasthe PCMS `Norin 26' showed partial male sterility. APCMS line showing complete male sterility, such as thePCMS `Fujimikomugi', should produce F1 seeds withhigh purity. However, the PCMS `Fujimikomugi' showeda lower female fertility. For practical use, it isnecessary to produce PCMS lines having high malesterility with high female fertility under long-dayconditions.

Photoperiod-sensitive cytoplasmic male sterility in wheat: nuclear-mitochondrial incompatibility results in differential processing of the mitochondrial orf25 gene.

An alloplasmic wheat line with the cytoplasm of Aegilops crassa expresses photoperiod-sensitive cytoplasmic male sterility (PCMS). Southern- and Northern-hybridization analyses showed that this line contains alterations in both the gene structure and transcription patterns of the mitochondrial gene orf25. In this study, the nucleotide sequence around the orf25 gene of Ae. crassa (CR-orf25) and common wheat (AE-orf25) was determined, and we found that the upstream region of CR-orf25 had been replaced by that of rps7 of common wheat (AE-rps7) through recombination. A novel open reading frame (orf48) is present upstream of CR-orf25. In these three genes, transcription was initiated from the consensus promoter motif of plant mitochondrial genes located in the upstream regions. Processing enzymes in Ae. crassa and common wheat cleave the respective precursor mRNAs, namely CR-orf25 and AE-rps7, at sites similar to that of the premature mitochondrial 26S rRNA. In contrast, the precursor mRNA is not effectively processed at the target sequence of CR-orf25 in the alloplasmic wheat line. Because major transcripts of the euplasmic CR-orf25 and AE-rps7 genes would result in a truncated orf48 product, one possibility is that the orf48 protein might disturb mitochondrial function at a specific stage and hence affect the expression of the PCMS trait.

Hybrid wheat breeding utilizing photoperiod-sensitive cytoplasmic male sterility.

Hybrid wheat breeding utilizing photoperiod-sensitive cytoplasmic male sterility.

Effect of Alien Cytoplasms on Meiosis in the F1 Hybrids between Alloplasmic Lines of Triticum aestivum cv. Chinese Spring and Rye or Triticale.

Chromosome pairing in MI of the PMC's was studied using the F1 hybrids between alloplasmic lines of a common wheat, Triticum aestivum cv. Chinese Spring (genome constitution AABBDD) as the female and rye (RR) or hexaploid triticale (AABBRR) in order to determine the effect of alien cytoplasms on meiotic chromosome behavior. The hybrids were obtained by embryo culture. Chromosome pairing in the hybrids of the first cross combinations (genome constitution ABDR) was entirely ascribable to the pairing between the homoeologues, whereas that in the hybrids of the second cross combinations (AABBDR) was due to both the homologous and homoeologous chromosome pairing. A D2 cytoplasm of Ae. crassa 4x promoted the homoeologous pairing but inhibited the homologous pairing. The S1 cytoplasm of Ae. sharonensis, another D2 cytoplasm of Ae. juvenalis, a G cytoplasm of T. timopheevi and an Sv cytoplasm of Ae. variabilis promoted whereas the Sb cytoplasm of Ae. bicornis inhibited the homoeologous pairing. Another Sv cytoplasm of Ae. kotschyi inhibited both the homoeologous and homologous pairing. The alloplasmic F1 hybrids from the first cross-combinations were crossed to an octoploid triticale (AABBDDRR) and the offspring were examined for their somatic chromosome number to estimate the effect of alien cytoplasms on the production of unreduced female gametes by the F1 's. Although the effect of individual alien cytoplasms could not be confirmed because of very low success in this cross, the overall frequency of the functional, unreduced gametes was estimated to be about 33%. Male-sterile octoploid triticales hav-ing the G-, Sv-, D2-and M-type cytoplasms were obtained for the first time by these crosses. Three alloplasmic octoploid triticale lines having D2-type cytoplasms showed photoperiod-sensitive cytoplasmic male sterility.

F1 Seed Production Efficiency by Using Photoperiod-sensitive Cytoplasmic Male Sterility and Performance of F1 Hybrid Lines in Wheat.

Photoperiod-sensitive cytoplasmic male sterility (PCMS) caused by Aegilops crassa cytoplasm to common wheat (Triticum aestivum) under long-day conditions (≥15 h light period) has been reported as a new means of producing hybrid wheat, that is a “two-line system”. The PCMS Iine is Inaintained by self-pollination under short-day conditions (≤14.5 h light period), and F1 seeds can beproduced by outcrossing of the PCMS Iine with a pollinator under long-day conditions. A cross pollination study for producing F1 seeds was carried out using three PCMS Iines and three restorer lines under a long-day condition at Tanno, Hokkaido, Japan. Seed setting rate was 14-33%, and 19-55 g/m2 F1 seeds with 47-88% hybrid purity were obtained. Variation in seed setting rate attributable to male parents was highly significant. High seed setting rate was achieved by using a pollinator taller than the PCMS Iine. Shriveled and preharvest sprouting kernels were found in the out-crossed F1 seeds, resulting in lower volume weight and germination rate than the selfed seeds of original cultivars of the PCMS Iines. A field test of evaluating four F1 hybrids with high hybrid purity (>65 %) was conducted under a short-day condition at Kasai, Hyogo, Japan. All F1 hybrids exhibited higher grain yield than their respective better-parent because of more spikelet number/ear and higher 1000 grain weight. The top F1 hybrid yielded 40% more than the mid-parent and 37% more than the better-parent, suggesting a possibility of the practical use of this system for hybrid wheat breeding. F1 hybrids tended to show higher volume weight than their parental cultivars. This indicates that grain quality of the F1 hybrids with the Ae. crassa cytoplasm is not inferior to those of parental cultivars with the wheat cytoplasm.

Genetic analysis of fertility restoration against photoperiod‐sensitive cytoplasmic male sterility in Triticum aestivum cv. Norin 61

Abstract Triticum aestivum cv. Norin 26 with the Aegilops crassa cytoplasm becomes almost completely male sterile when grown under a long‐day condition (15 h of light or longer), but is highly male fertile under a short‐day condition (14.5h or less). This type of male sterility is called photoperiod‐sensitive cytoplasmic male sterility (PCMS). Genetic analyses were made of the fertility‐restoring (Rf) genes effective against PCMS that are present in T. aestivum cv. Norin 61. Conventional and monosomic studies indicated that restoration of fertility is controlled by multiple Rf genes located on at least four chromosomes: 4 A, 1D, 3D and 5D. The genetic mechanism of fertility restoration by the genes of‘Norin 61’differs from the mechanisms reported for‘Chinese Spring’and a‘Norin 26’mutant line.

Alloplasmic wheats with Aegilops crassa cytoplasm which express photoperiod-sensitive homeotic transformations of anthers, show alterations in mitochondrial DNA structure and transcription.

Alloplasmic wheat. Triticum aestivum cv. Norin 26, with Aegilops crassa cytoplasm, shows photoperiod-sensitive cytoplasmic male sterility (PCMS). This alloplasmic line expresses pistillody of anthers only when grown in long-day conditions (> 15 h light). To assess the molecular basis of the PCMS, we carried out Southern and Northern hybridization analyses on mitochondrial DNAs and RNAs isolated from seedlings of alloplasmic lines showing various PCMS phenotypes using probes for twelve mitochondrial genes. All RFLP patterns of mitochondrial DNA from alloplasmic lines greatly differed from those of common wheat, and were slightly changed from those of the parental species, i.e., Ae. crassa. This indicates that nuclear substitutions between related plant species induce structural alterations in the mitochondrial genome. Furthermore, RFLP patterns of (cr)-N61 and FR-mutant probed with coxIII and orf25 were identical with each other, but different from those of the other alloplasmic lines, indicating that the nuclei of N61 and FR-mutant harbor some gene(s) that induces structural alterations of the mitochondrial genome in the coxIII and orf25 regions. The transcription patterns of atp6 and cob in Ae. crassa type were different from those of T. aestivum type. Furthermore, the orf25 transcript in alloplasmic wheats was about 300 nucleotides longer than that of euplasmic lines, including the Ae. crassa pure line, suggesting that transcription patterns of orf25 are associated with recovery from the PCMS phenomenon. These data clearly show the mutual cross-talk between the nuclear genome and chondriome. These observations raise the possibility that the dysfunction of mitochondria caused by the failure of a cooperative control of mitochondrial gene(s) expression influences the pathway of flower morphogenesis, especially in the process that determines organ identity.

An EMS‐induced wheat mutant restoring fertility against photoperiod‐sensitive cytoplasmic male sterility

Triticum aestivum cv. ‘Norin 26’ with Aegilops crassa cytoplasm shows photoperiod‐sensitive cytoplasmic male sterility (PCMS). This alloplasmic line is almost completely male‐sterile under long‐day conditions (≥ 15h), but highly male‐fertile under short‐day conditions (≤ 14.5h). To obtain male—fertile mutants against PCMS, seeds of the alloplasmic line were treated with ethyl methane sulfonate (EMS). The M3 generation was evaluated for PCMS expression, and one fertility‐restoring (FR‐mutant) line showing high male fertility under the long‐day conditions was selected. Reciprocal F, hybrids between the FR‐mutant and the alloplasmic ‘Norin 26’ showed male sterility under the long‐day conditions, and continuous segregation with respect to the degree of fertility restoration occurred in their F2 generations. These results indicate that multiple recessive mutations with minor effects, induced in the nuclear genome, are involved in the fertility restoration. In fact, no restriction‐fragment‐length polymorphisms of mitochondrial DNA between the FR‐mutant and the alloplasmic ‘Norin 26’ are found.

Photoperiod-sensitive Cytoplasmic Male Sterility Induced in Japanese Wheat Cultivars by Transferring Aegilops crassa Cytoplasm.

Triticum aestivum cv. Norin 26 with Aegilops crassa cytoplasm shows photoperiodsensitive cytoplasmic male sterility (PCMS): The alloplasmic line is almost completely male sterile under longday conditions (≥l5 h light period), but highly male fertile under shortday conditions (≤14.5 h). To examine the effects of the Ae. crassa cytoplasm on other wheat cultivars, this cytoplasm was introduced into 17 Japanese wheat cultivars by repeated backcrosses. Among their alloplasmic lines which reached B5 (11 lines) or B4 (six lines) generation, those of nine cultivars showed PCMS caused by the Ae. crassa cytoplasm, while those of other eight cultivars did not. Thus, the former nine cultivars are converted to the PCMS Iines by transfer of the Ae. crassa cytoplasm, and the latter eight cultivars have demonstrated to carry fertilityrestoring (Rf) gene(s) against PCMS. Pedigrees of the Japanese wheat cultivars suggest monophyletic origin of the Rf gene(s).

Genetic analysis on the fertility restoration by Triticum aestivum cv. Chinese Spring against photoperiod-sensitive cytoplasmic male sterility.

Triticum aestivum cv. Norin 26 with Aegilops crassa cytoplasm shows photo-period-sensitive cytoplasmic male sterility (PCMS). This alloplasmic line is almost completely male sterile under a long-day condition (15 h light period), but highly male fertile under a short-day condition (14.5 h light period). The alloplasmic line of T. aestivum cv. Chinese Spring with the same cytoplasm does not express PCMS. Conventional and telosomic analyses revealed that the fertility restoration manifested by Chinese Spring is controlled mainly by a single dominant gene (designated Rfd1) located on the long arm of chromosome 7B, and that a large number of modifiers are involved in modifying the level of fertility restoration. The function of the Rfd1 gene is expressed sporophytically. A slight certation was observed between the two types of pollen grains, one carrying and the other not carrying this gene, under the presence of Ae. crassa cytoplasm.

Genetic analysis on the fertility restoration by Triticum aestivum cv. Chinese Spring against photoperiod-sensitive cytoplasmic male sterility

Genetic analysis on the fertility restoration by Triticum aestivum cv. Chinese Spring against photoperiod-sensitive cytoplasmic male sterility

Photoperiod-sensitive cytoplasmic male sterility in wheat with Aegilops crassa cytoplasm

Triticum aestivum cv. Norin 26 with Aegilops crassa, Ae. juvenalis or Ae. vavilovii cytoplasm (all D2 type) has been studied relative to its photoperiodic response of male sterility and fertility restoration patterns. Alloplasmic lines of ‘Norin 26’ with a D2 type cytoplasm showed almost complete male sterility under long-day conditions (≥15 h), but high male fertility under short-day conditions (≤14.5 h). No significant influence of temperature on reduction in male fertility was observed. Thus, this type of male sterility is called ‘photoperiod-sensitive cytoplasmic male sterility’ (PCMS). The PCMS is expressed in the form of pistillody of stamens. Histological studies revealed that there were incomplete ovule-like structures instead of tapetal cells and pollen grains in the pistillate stamens. The floret differentiation stage of the plant is the stage that is sensitive to photoperiod. The PCMS can be used as a new means for hybrid wheat production, named ‘two-line system’. The PCMS line is maintained and multiplied by self-fertilization under short-day conditions, and hybrid seed can be produced by crossing the PCMS line with a pollinator line under long-day conditions. In contrast to the system of hybrid wheat production using the T. timopheevi cytoplasm, the present system requires only PCMS and pollinator lines.