The phenomenon of cytoplasmic male sterility (CMS)

Cytoplasmic male sterility (CMS, English Cytoplasmic male sterility, CMS) - the phenomenon of complete or partial sterility of androecium higher plants, the cause of which is the presence of a special mutation in the mitochondrion, that is, in the genome of mitochondria, plant fertility is restored completely or partially in the presence of a dominant allele of the nuclear fertility restorer gene. First described by Marcus M. Rhodes in corn, it has also been described in petunias, cabbages, sunflowers, and other plants. CMS is characterized by the so-called maternal type of inheritance.

General CMS mechanism

Cytoplasmic male sterility is manifested in the interaction of the nuclear genome with the mitochondrion. Mitochondria and plastids, as organelles originating from endosymbiotic prokaryotic microorganisms, have their own unique genome, and although in the process of evolution of the eukaryotic cell they lost most of their autonomy and lost most of the genes, some important proteins are still encoded under the control of mitochondrial and plastid genes. Mitochondria and plastids also have a working protein-synthesizing apparatus. Cytoplasmic male sterility occurs as a result of a certain mutation in the mitochondrion, resulting in degeneration of the androecium of the plant, manifested either in degeneration of the anthers, or in the non-opening of the anthers, or in the formation of non-viable pollen. Genotypes with wild-type mitochondria are designated N or Cyt N (i.e., normal type of cytoplasm), genotypes with mutant mitochondrions are designated as S or Cyt S (i.e., sterile cytoplasm). In the nuclear genome of plant cells, there are also special genes that restore fertility (eng. restorer of fertility or RF-genes), the dominant alleles of which completely or partially restore androecium fertility. Only genotypes that have a mutant mitochondrion and are recessive homozygotes for RF-genes are sterile (Cyt S rfrf), all other genotypes are fertile.

Selection of F1 hybrids of white cabbage based on CMS

The use of F1 hybrids of maternal forms with cytoplasmic male sterility (CMS) in seed production excludes self-pollination and the presence of sibs in batches of hybrid seeds.

Male sterility is found in almost 140 species of higher plants and is associated with abnormal development of anthers (unopened anther or aborted pollen on various stages microsporogenesis (Bunin, 1994). The cause of CMS are mutations in mitochondrial DNA (mt-DNA), which are transmitted to offspring during seed propagation of maternal plants.

After the discovery of specific dominant fertility restorer genes (Rf genes), it became possible to commercially use CMS lines as maternal parental forms of such important agricultural plants as corn, sorghum, rice, and sunflower.

At plant species Bgassicaceae L. (as well as onions,

beets and carrots), a more complex inheritance of MS is observed, which until recently was reflected in the effectiveness of its use in heterotic breeding. The phenotypic manifestation of male sterility in cabbage plants is more often due to the interaction of the cytoplasm with the nuclear genes that are in the homozygous state, that is, in essence, it refers to nuclear-cytoplasmic male sterility. Therefore, unlike, for example, corn, this requires the creation of special lines - sterility fixers, which complicates the selection and seed production process. At the same time, in vegetable cruciferous crops of such species as B. oleracea, B. campestris, R sativus, there is no need to restore fertility, since these plants use vegetative organs for food.

Among the plant diversity of species Bgassica L., the form with nuclear-cytoplasmic MS was first discovered by Ogura (1968) in an unidentified variety of the Japanese radish subspecies - daikon. Flowers in plants of this form have a number of morphological features: small buds, a loop-shaped or pistil protruding from the bud, the death of the first buds on the inflorescence, etc. Pollen degeneration in such daikon MS plants occurs at the stage of microsporogenesis and is associated with early collapse of the tapetum tissue. This type of sterility is induced by the interaction of the sterile cytoplasm S (og) with the homozygous recessive nuclear gene msms (rfog rfog) (Bunin, 1994).

In Russia, attempts to use male sterility were made at TSKhA and at VNIISSOK. In TSHA Z.G. Averchenkova in the early seventies discovered several plants with nuclear cytoplasmic male sterility in the Amager611 variety (Averchenkova, 1968). This type of male sterility could not be used in practical breeding because sterility fixers were not obtained. THEM. Kolesnikov (VNIISSOK) introduced androsterile lines of broccoli from the Czech Republic.

According to the phenotypic manifestation of male sterility, these lines most likely possessed ogi-CMS. Attempts to use these lines directly in the breeding process were not successful due to their shortcomings: the absence of petals in flowers, the death of buds when adverse conditions etc.

Thus, for a long time, obtaining cabbage hybrids based on male sterility was very problematic.

Type of YCMS, according to A.V. Kryuchkova (1974) has a number of disadvantages:

1) it is difficult to maintain the JCMS line in a state homozygous for most genes, since the sterility fixer may be with a different genotype and, as a result, the F1 hybrids will be misaligned;

2) when seeding lines and hybrids, seeds are collected only from a sterile line and their yield is significantly reduced.

CMS donors were not found in cabbage. In 1988 M.S. Bunin introduced the male-sterile form of daikon from Japan to Russia. Hybridological analysis showed that its androsterility is controlled by the interaction between the recessive nuclear gene in the homozygous state msms and the sterile cytoplasm (S), that is, it corresponds to ogi-CMS.

There are currently several CMS systems in oilseed cruciferous crops. Widespread use in breeding programs for the creation of hybrids of oilseed rape was polima-CMS, which was identified as a spontaneous mutation in the Polish variety of rapeseed.

Sterility fixers were found in rapeseed, the fertility restorer was isolated in the rapeseed variety Italu and in Vg. jincea. On the basis of polima-CMS, F1 hybrids of spring rapeseed were created and registered: in China - Qui - Yong, in Canada - Hyola 401, in Europe - Hybridol. The jun-CMS (B. jincea) system is more stable than the polima-system, and F1 hybrids with partially restored male fertility were obtained on its basis in Indian mustard and oilseed rape.

The par-CMS system, identified by Thompson (1976) and Shiga (1976) in B. parus, is rarely used in heterotic breeding of oilseed rape due to MS instability in the temperature range from 20 to 26°C.

The sam-CMS system (B. sampestris) was identified as fairly close to the nap system with corresponding drawbacks when used in the selection of heterotic hybrids.

The nigra-CMS system. Obtained by transferring the genome of B. napus and B. oligracea into the cytoplasm of B. nigra. It is highly stable in B. olegacea and low in B. nigra. With this system, the anthers are modified into petals (petaloid sterility - pp):

male sterility (b) pp (b - B. nigra cytoplasm);

sterility fixer (s) pp (s - cytoplasm

V. found in fodder and cabbage;

fertility restorer (c) PP, found in fodder and cabbage.

Tor-CMS system. Based on B. tourneforii. Used to create the first B. juncea hybrids.

The mug-CMS system. Found after the transfer of the nucleus of B. napus into the cytoplasm of Diplotaxis muralis. Transferred to turnip and rapeseed. The manifestation is stable, but there is no fixative of sterility.

In recent years, in a number of countries (Holland, Denmark, Belgium, France, Japan) breeding work has been successfully carried out on the use of cabbage forms with CMS.

In Russia, in the RGAU - Moscow Art Academy named after. K.A. Timiryazev at the Selection Station named after N. N. Timofeeva continued the earlier work on the discovery and use of forms of cabbage with CMS. As a result of the work carried out, a hybrid of medium-late cabbage Favorit was created using CMS. The high efficiency of the method of distant hybridization in the transfer of CMS from rapeseed (B. napus) to cabbage (B. pekinensis) has been established.

Thanks to cytoplasmic male sterility, hybrids have become widespread in production. received a huge economic effect, as the cost of manual labor for the production of seeds of hybrids has significantly decreased. CMS was discovered by Rhodes in 1931 and M. I. Khadzhinov in 1932. The first attempt practical use her in maize breeding belongs to Ritchie and Wallace, but it ended in failure, since the source of sterility discovered by Rhodes did not show stability for this trait. And only after the discovery by Mangelsdorf and Jenkins of new sources of sterility, work in this direction was resumed. The first sterile-based simple hybrids in the United States were obtained by Jones and Mangelsdorf in 1947-1948.

The practical use of the CMS system in maize suggests the following factors.

1. Creation of hybrids corresponding in terms of yield and other indicators.

2. Transfer to a sterile basis of the maternal forms of the hybrid (line, simple hybrid, variety) - the creation of sterile analogues.

3. Transfer of the restoring ability to lines or other forms used as paternal ones - the creation of analogues - fertility restorers.

Methods for obtaining hybrids have been described above, and methods for creating sterile analogues and analogues - fertility restorers are also described here. A genetic study of the CMS system showed that pollen sterility manifests itself only when the “sterile” cytoplasm is combined with the rf genes in a recessive state. In the dominant state, the Rf genes inhibit the action of the “sterile” cytoplasm without changing its structure.

According to Jones' hypothesis, CMS is controlled by the plasma-nuclear system, which includes plasmogens (specific elements of the cytoplasm capable of self-reproduction and transmitted through the cytoplasm of the maternal germ cell) and genes localized in chromosomes.

Currently, several types of corn sterility are described, but two are used in our country: Texas and Moldavian. The latter is identical to the type of sterility known in the USA under the index 5, or 118 VA.

Moldavian and Texas types of sterility differ from each other in their specific response to genes - fertility restorers. For example, it was found that the VIR 44 line is a sterility fixer for forms with the Moldavian type of sterility and a fertility restorer for Texas-type CMS. In plants with the Texas type of sterility, the anthers are completely sterile, while plants of the Moldavian type of sterility may have a small percentage of fertile pollen grains in the anthers, but the anthers do not open. The Moldavian type of sterility is more common.

The transfer of self-pollinated lines to a sterile basis (the creation of sterile analogues) is carried out by the backcross method. At the same time, the breeder must take into account that in some cases the “sterile” cytoplasm has a depressing effect on the development of such traits as the height of attachment of the upper cob, the length of the panicle, the total number of leaves, and some others. For example, a sterile analogue of the self-pollinated Illinois 90 line reduces plant height by 12% compared to the fertile form. It has been established that Moldavian-type CMS causes less depression than Texas-type CMS.

The creation of sterile analogues is facilitated by the fact that the majority of the created self-pollinated lines (94-96%) belong to sterility fixers.

Comparison of the productivity of sterile and fertile analogues of simple, double and varietal hybrids showed that the transfer of hybrids to a sterile basis does not affect their productivity.

The breeder should be aware that the relative value of the Texan and Moldavian types of CMS in hybrids is the same. Therefore, he can choose the most convenient source of CMS for him when transferring the created hybrids to a sterile basis.

In the program of maize breeding using CMS, the creation of analogues - fertility restorers occupies a central place. This is explained by the fact that among the self-pollinated lines used by breeders, lines that restore fertility are extremely rare (4-6%).

Analogues - fertility restorers are usually created by the backcross method or isolated from various populations. In saturating crosses, dominant genes - fertility restorers (Rf) are transferred to the genotype of lines that are sought to be given a restorative ability. There are several schemes for creating analogues - fertility restorers. The most common of them are: the creation of such analogues on a fertile basis, on a sterile basis (the method of E. Eckhard and M. I. Khadzhinov) and the combined scheme proposed by M. I. Khadzhinov and E. I. Vakhrusheva.

Below are the most common schemes for creating analogues-restorers of fertility (according to M. I. Khadzhinov).

I. Creation of analogues - restorers of fertility on a fertile basis.

1. Crossing fertility restorer B with line A: B×A.

2. First saturating cross: (B×A)×A.

3. Second saturating cross [(B×A)×A]×L.

Simultaneously with the second backcross, each plant involved in the work is tested for reductive capacity by pollinating its sterile form with pollen. For further saturation, plants with a restorative ability are used. Subsequently, saturating crosses with a parallel check for reductive capacity are repeated 4-5 times, and then the selected forms are subjected to self-pollination twice. In self-pollination, plants are also tested for resilience by crossing with a sterile analyzer. The need to carry out a constantly large number of analyzing crosses makes it very difficult to work according to this scheme. Therefore, the following scheme is more convenient.

II. Creation of self-pollinated analogues - fertility restorers on a sterile basis.

1. Crossing of a sterile form (Tc) with a reducing agent (B): Tc×B.

2. Crossing a fertile hybrid (Tc×B) with line A, which seeks to create an analogue - a fertility restorer.

3. Second crossing of fertile hybrid plants with line A: [(Tc×B)×A]×A.

4. Third crossing of fertile plants with line A: ([(Tc×B)×A]×A)×A.

5. Fourth crossing of fertile plants with line A: /([(Tc×B)×A]×A)×A/×A.

6. Self-pollination of fertile plants (Tc×B)×A4.

7. Repeated self-pollination of fertile plants (Tc×B)×A4.

8. Selection of offspring that do not produce sterile plants.

When carrying out work according to this scheme, the need for analyzing crosses with a sterile analyzer is completely eliminated, since only fertile forms with sterile cytoplasm are selected for work, that is, forms that carry genes that restore fertility.

If a sterile analogue (ATS) has already been created for the line to which they want to give the property of recovery, the scheme of work is somewhat simplified.

Self-pollination should be carried out until the separation of sterile plants ceases. The disadvantage of this scheme is the reduced productivity of pollen formation created analogues - restorers of fertility on a sterile basis. This is especially pronounced in unfavorable growing conditions. To correct this shortcoming, a combined scheme was proposed.

III. Combined scheme for creating analogues-fertility restorers. After six saturating crosses on sterile cytoplasm, the order of crosses is changed. The usual fertile analogue of the self-pollinated line is used as the maternal form, according to which an analogue is created - a fertility restorer, and as the paternal form - a saturated heterozygous line on the sterile cytoplasm. The resulting plants are subjected to self-pollination twice with simultaneous verification of the genotype on a sterile tester. This order of work allows you to select a homozygous line - a restorer on a fertile basis.

It is promising in maize breeding to create universal analogues - fertility restorers. Their existence was first pointed out in 1965 by Jones, who identified the lines NC77, Ku21, and Tx-127C on this basis.

The possibility of creating universal fertility restorers is based on the following provisions.

1. The restoration of fertility in the Texas-type cytoplasm is determined by the action of two complementary genes - Rf1 and Rf2 in the dominant state, and in the Moldovan-type cytoplasm by the dominant Rf3 gene.

2. Most forms of corn carry the Rf2 gene, and the difference between the fertile and sterile forms in the Texas type of sterility is whether or not the Rf1 gene is present.

3. The Rf1 and Rf3 genes are located in different chromosomes and can easily be combined in one individual.

When transferring seed production of hybrids to a sterile basis according to the full recovery scheme, the breeder sometimes has to change the order of combination of lines in the hybrid, when it is impossible to create a sterile analogue or reductant analogue for individual lines that are part of the hybrid.

Similar transformations had to be done with the hybrid Krasnodarsky 309 [(W 155 × W 23) × (VIR 38 × Cr 25)], since the W 155 line is a partial fertility restorer and it is impossible to create its sterile analogue. In this regard, it was advisable to use the W 155 line as the paternal form. The new formula of the hybrid Krasnodar 309T: [(W 23T × VIR 38) × (W 155 × Cr 25)]. Tests showed that such a rearrangement did not affect the productivity of the hybrid. Thus, observations show the possibility of changing the formulas of simple and double interline hybrids in some cases without compromising their yield.

Despite the fact that heterosis is observed in very many plant species, in practice this phenomenon of hybrid vigor is still used in a relatively small number of crops. The reason for this is due to the difficulties in the production of hybrid seeds associated with the structure and shape of the reproductive organs in some species.

By picking off the cobs of corn, which is a monoecious plant, it is easy to remove the male reproductive organs from the mother forms and thus obtain a sufficient amount of hybrid seeds. However, the castration of anthers of sunflower, rice, wheat, having bisexual flowers, is difficult and economically unprofitable. Therefore, appropriate methods are needed for the production of hybrid seeds, of which the method of using male sterility is currently considered the most successful.

male sterility

Male sterility is a phenomenon associated with the production of pollen by plants that is not capable of fertilization. It arises as a result of the complete underdevelopment of the male reproductive organs (anthers) or in those cases when normal microspores are not formed in normally developed anthers due to violations of meiosis and the pollen becomes non-functional, or sterile.

There are three types of genetically determined male sterility:
1) genetic, or nuclear, male sterility, due to the action of one or more genes in the chromosomes;
2) cytoplasmic male sterility due to extrachromosomal factors, or plasmogens;
3) cytoplasmic-nuclear male sterility, due to the action of both factors.

Of these types of sterility, cytoplasmic male sterility turned out to be the most suitable for plant breeding.

Cytoplasmic male sterility (CMS)

This type of sterility occurs spontaneously in corn, sugar beets, carrots, onions, peppers and other plants. The sources of cytoplasmic male sterility currently used are obtained mainly from crosses between different species (wheat, rice, tobacco, common beans, peppers, cruciferous species, etc.) or even from crosses between different genera (Aegilops ssp. X Triticum ssp.).

When a cytoplasmic male-sterile plant is crossed with a male-fertile plant, male-sterile offspring are produced. This shows that plasmogens located in the cytoplasm are responsible for the sign of CMS. They are transmitted to offspring only through the eggs, since the paternal form transmits only the nucleus through pollen grains and therefore is not able to cause male sterility in the offspring. It was further established that cytoplasmic male sterility, as such, cannot be used independently in the selection of heterotic hybrids, since when crossing CMS lines with any other lines, sterile F1 hybrids are obtained. In onions and other plants where vegetative parts are used from F1, this does not present any particular difficulties, but in sunflower, corn and other plants whose main product is seeds, CMS cannot be used. Therefore, the paternal line (pollinator) must contain genes that restore male fertility, the so-called Rf genes, in order for F1 plants to produce seeds.

The production of hybrids using CMS lines can be represented as the following technological scheme:
1) the transfer of the sign of the cms of the line that will serve as the maternal form;
2) maintenance of the CMS-line (A-line) and its fertility restorer, or analogue (B-line);
3) transfer of the Rf gene to the pollinator line (R line);
4) production of hybrid seeds by growing in alternating rows of lines A and R.

After the selection of the CMS trait, it is transferred to the corresponding line or variety using the backcrossing method. After at least six backcrosses of the cms line with the paternal line, an A line is obtained containing all the paternal traits and additionally the cms trait. Maintenance of the A-line is achieved by crossing it with the original line, which does not have CMs (B-line), which is actually its isogenic line, or a fertile analogue.

Since all normal lines, i.e. those without CMS also do not carry fertility restoring genes (Rf genes), it is necessary to find lines that contain these genes. They are usually found in a part of the material that is of the same species as the CMS material, but in some cases these genes can even be passed on through crossbreeding. different types, such as the transfer of the Rf gene from Triticum timopheevi to Tr. aestivum. The transfer of Rf genes to pollinating lines (R lines) is also carried out with the help of backcrosses, this is necessary in the species used to obtain seeds. At the same time, species that use vegetative parts (onions, grasses) do not need pollinating lines with the Rf gene.

If the chromosomes of the pollinator line contain the Rf gene (or genes), this means that the cms line, along with the so-called sterile cytoplasm, also contains nuclear genes that are unable to restore fertility, i.e. gene (or genes) rf. The production of hybrid seeds based on cytoplasmic male sterility is shown schematically in Figure 16.1.

The production of hybrid seeds based on CMS is fraught with many difficulties. The very sign of male sterility is not fully manifested, since even in A-lines, for example, a certain number of fertile plants appear. RF genes can be strongly influenced by factors environment, so even F1 plants are not fully fertile, which ultimately reduces the effect of heterosis. Along with the changes taking place in the A- and R-lines, there is often a weakening of resistance to pathogenic organisms compared to their normal counterparts, etc.

Nuclear male sterility

In most species, nuclear, or genetic, or rather gene, male sterility is due to one recessive gene (sorghum, common beans), but can be controlled by a large number of genes (barley, tomatoes). Since we are talking about genes located on chromosomes, splitting occurs in the offspring of the maternal and paternal lines, and technological process production of hybrid seeds differs from that based on WMS (Figure 16.2).

The difficulties in using nuclear male sterility are as follows: first, fertile plants must be eliminated before flowering so that they do not pollinate male sterile plants, as this reduces the effect of heterosis; secondly, due to the dominance of the male fertility gene (Ms), it is necessary to grow twice as many plants as it is necessary for seed production (all Msms plants are eliminated).

In an attempt to overcome these difficulties, Ramage applied the so-called balanced tertiary trisomic system, or BTT system, to barley. Its meaning is to obtain trisomic plants with one additional chromosome, which includes a segment of two non-homologous chromosomes. The extra chromosome carries the Ms gene, and the two normal homologues of the chromosome contain the ms genes. The extra chromosome is not passed on to offspring through the paternal line. The progeny of a trisomic plant splits into ~70% disomics (diploid, always male sterile, msms) and ~30% trisomics (fertile, Msmsms). Ramage managed to transfer the marker gene for anthocyanin stem color to the additional chromosome, which made it possible to distinguish between sterile and fertile plants. However, this method has not been widely used in practice, since it is rather complicated; in addition, BTT plants are weakened and produce fewer seeds than normal ones.

Functional male sterility

In this type of male sterility, the plants produce normal pollen, but the anther opening mechanism is disrupted and pollen grains are not released from the anthers. Nevertheless, functional male sterility can be successfully used to produce hybrid seeds.

Plants with functional male sterility serve as maternal parent forms, they do not need to remove anthers. Some other line is taken as the paternal form, and it is not necessary that it contains genes that restore fertility.

This type of sterility is found in tomatoes, eggplant, blackberries and some other species. In Bulgaria, several tomato hybrids have been created on the basis of functional male sterility.

Chemical induction of male sterility

In plants with bisexual flowers, where it is difficult to obtain forms with cytoplasmic or nuclear male sterility, and mechanical removal anthers is economically unprofitable, the sterility of pollen is sought to be caused by chemical means, without damaging the pistil and ovary.

It has been established that such chemicals, like etrel (2-chloroethanephosphoric acid) or mendoc (2,3-dichloroisobutyrate), sterilize wheat, rice, sugar beet pollen; gibberellic acid (which is also a growth stimulant) has the same effect on lettuce, onions, sunflowers, etc. All these substances are collectively referred to as gametocides.

Successful induction of male sterility using gametocides would make it possible to reduce the cost and speed up the commercial production of hybrid seeds without the use of a lengthy procedure for transferring the CMS plasmogen and the Rf gene. However, modern gametocides have a number of negative effects. First of all, they cause incomplete sterility of pollen grains; in addition, their activity depends on the doses and timing of treatments, which must be repeated several times during the growing season. Gametocides also cause damage to the female generative organs, lead to deformation of the plants themselves and lengthen the growing season. For all these reasons, they have not yet received wide recognition in practice, but nevertheless work on the creation of new gametocides and on the improvement of methods for their application continues.

Plants are restored completely or partially in the presence of a dominant allele of the nuclear gene-fertility restorer. First described in corn by Marcus M. Rhodes, also described in petunias, cabbages, sunflowers, and other plants. CMS is characterized by the so-called maternal type of inheritance.

General CMS mechanism

Manifested in the interaction of the nuclear genome with the mitochondrion. Mitochondria and plastids as organelles, originating from endosymbiotic prokaryotic microorganisms, have their own unique genome, and although in the process of evolution of the eukaryotic cell they lost most of their autonomy and lost most of the genes, some important proteins are still encoded under the control of mitochondrial and plastid genes. Mitochondria and plastids also have a working protein-synthesizing apparatus. Cytoplasmic male sterility occurs as a result of a certain mutation in the mitochondrion, resulting in degeneration of the androecium of the plant, manifested either in degeneration of the anthers, or in the non-opening of the anthers, or in the formation of non-viable pollen. Genotypes with wild-type mitochondria are designated N or Cyt N (i.e., normal type of cytoplasm), genotypes with mutant mitochondrions are designated as S or Cyt S (i.e., sterile cytoplasm). In the nuclear genome of plant cells, there are also special genes that restore fertility (eng. restorer of fertility or RF-genes), the dominant alleles of which completely or partially restore androecium fertility. Only genotypes that have a mutant mitochondrion and are recessive homozygotes for RF-genes are sterile (Cyt S rfrf), all other genotypes are fertile.

CMS in corn

At corn ( Zea mays) several types of CMS are known, the most studied are the so-called. T-type CMS (also called Texas), C-type CMS (so-called charrua type, also called Paraguayan and Colombian) and S-type CMS (also called Moldavian or M-type CMS). Each type of CMS is determined by its specific mutation in the mitochondrion and is restored by its fertility restorer genes. Thus, T-type CMS is caused by a mutation in the T-urf region of the mitochondrion, as a result of which mitochondria begin to produce the mutant toxic Urf 13 protein, which in turn leads to degeneration of the tapetum cells, which leads to the formation of a male-sterile maize phenotype, the gene Rf1, located in the centromeric region of the short arm of chromosome 3, produces mitochondrial aldehyde dehydrogenase mtALDH, which removes the toxic effect of the chimeric protein and leads to the restoration of fertility. Gene Rf2, located in the centromeric region of chromosome 9, complementarily interacts with the gene Rf1, and to restore fertility in maize lines with T-type cytoplasm, both genes must be in a dominant state. The S-type of CMS is due to a mutation in the orf355 and orf77 open reading frames, resulting in a chimeric nucleotide sequence R orf355-orf77 . The fertility restorer gene is Rf3, due to postmeiotic restoration of fertility, genotypes Rf3rf3 form 50% of fertile pollen. It was shown that Rf3 affects the levels of expression of mitochondrial and nuclear genes and has a pleiotropic effect at the level of transcription. A possible mechanism of S-type CMS in maize is a change in the level of gene expression in orf355-orf77 plants and the inclusion of the mechanism of programmed cell death, while the restoration of fertility is due to the normalization of the level of transcripts in mitochondria and inhibition of apoptotic mechanisms. gene expression product Rf3 changes the expression level of the orf355-orf77 chimeric sequence. The C-type of CMS is caused by a mutation in the genes of ATP synthase and the formation of a chimeric ATP synthase atp6-atp9 of the type, the C-type of CMS is restored by genes Rf4, Rf5 And Rf6.

Notes

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