From the present investigation, three different type of true breeding wild aborted cytoplasmic genicmalesterility systems: i) iCMS-WA, ii) rTCMS-WA and iii) TCMS-WA with majority panicles completely exserted were developed from the segregating self-population of conventional CMS-WA parents. Hence, these three groups of malesterility system itself prove the existence of at least 3 different nuclear genes, one each responsible for conditioning iCMS-WA, rTCMS-WA, and TCMS-WA character. Of these genes, only the recessive ‘fr’ gene in iCMS-WA is well documented. The phenomenon of pollen abortion in rice-CMS is known for the incompatibilities between mitochondrial-nuclear genomic (‘ms’ - 'fr' genes) interactions (Fuji et al. 2010). But no information is yet available in rice about these two thermo-sensitive genes. However, when these two thermo-sensitive genes simultaneously exist along with recessive 'fr' gene, as in the heterozygous parents or in early generation heterozygous breeding materials, one is expressed depending upon the environmental threshold while expression of the other remains suppressed and this relationship is reciprocal. That is why, heterozygous parent lines and/or early generation heterozygous breeding materials showed sterility in the cold environments, alteration to fertility in the warm environments (rTCMS character) and again conversion to high sterility in the still warmer environments of mid- and late-summer (TCMS character) (Figure1b). This suggests a non-allelic relationship between these two thermo-sensitive nuclear genes. Since environment is the main driving force to trigger gene expression in such cases, it appears that in absence of proper environmental threshold, none of these two thermo-sensitive genes would produce its full phenotypic expression. Therefore, while working with such type of heterozygous conventional CMS-WA sterility, there is no wonder while working, different workers would report different degrees of malesterility and/or fertility in these lines.
Genicmalesterility (GMS) is one of the most important economic traits for cotton (Gossypium hirsutum L.) hybrid seed production. The GMS trait conferred by two recessive alleles ms5 and ms6 in homozygous constitu- tion is widely used for cotton hybrid seed production in India. Identification of molecular markers closely linked to the ms5 and ms6 alleles would be useful in effective transferring in a short time male-sterility genes into cultivars or elite lines using marker-assisted backcrossing. Here, we describe a quick method to identify markers for GMS genes using bulk segregant analysis (BSA) in the interspecific (G. hirsutum × G. hirsutum) biparental population. The parents and bulks were genotyped with a cotton single nucleotide polymorphism (SNP) 63K ar- ray that contains 63 058 SNP markers including 45 104 intraspecific and 17 954 interspecific SNP markers. Four SNP markers were found to be linked with the Ms5 and Ms6 genes. The markers i23493Gh and i46470Gh linked with the Ms5 gene, and other two markers i08605Gh and i08573Gh linked with the Ms6 gene are located on chromosome 12 and 26, respectively. A simple and cost effective tetra-primer amplification refractory mutation system PCR (tetra-primer ARMS-PCR) assay was optimized for screening a large number of breeding samples with the identified SNP markers in a short time. The molecular markers developed in this study will facilitate the marker-assisted selection (MAS) and accelerate the development of new GMS lines to use in cotton hybrid seed production.
Rice is the third major food crop in Kenya and, its production is estimated at 129,000 tons which is below the annual national demand of 548,000 tons. Kenya rice yields per hectare are very low compared to major producers like China. Basmati (B) varieties, B370 and B217, are preferred by most rice consumers and are cultivated as a cash crop by 98.8% of Mwea rice farmers. This is because they have strong aroma. Due to the demand, basmati rice command high premium prices locally and internationally. Unfortunately, low yielding traits is a phenomenon shown by all basmati cultivars. To improve on yield, this study exploited hybrid rice technology using greenhouse structure to emasculate medium height, environmental sensitive genicmalesterility (EGMS) lines for crossing with viable pollen from basmati lines for hybrid basmati rice production. EGMS lines namely, photoperiod sensitive genicmale sterile (PGMS) and thermosensitive genicmalesterility (TGMS) were crossed with local basmati varieties. Marker assisted selection (MAS) was used to identify F 1 hybrids from various crosses. Results indicated
Although we do not know if the malesterility at the LTMS locus is due to dominant genicmalesterility caused by the Lebed allele alone or indica-japonica hy- brid malesterility caused by interaction of the Lebed and T65 alleles, our study demonstrates that the hetero- zygous Lebed allele of the LTMS gene acts as a domin- ant sporophytic pollen killer in a nuclear background of japonica T65. The LTMS line, therefore, can be used as a dominant male sterile line in recurrent selection breeding for facilitation of population improvement of japonica rice.
In striking contrast to Drosophila species, we have shown a simple genetic basis for hybrid malesterility between M. guttatus and M. nasutus. In the simplest version of the Dobzhansky–Muller model, postzygotic reproductive isolation evolves due to a genetic incom- patibility between a single pair of heterospecific factors. However, as M uller (1942) himself discussed, hybrid incompatibilities might very well involve more than two genes. In fact, theory predicts that complexity may facilitate the evolution of hybrid incompatibilities by allowing ancestral species to circumvent deleterious genotypic combinations (O rr 1995). Hybrids between subspecies of D. pseudoobscura suffer no reductions in male fertility unless they carry incompatibility alleles at a minimum of four loci (O rr and I rving 2001). Likewise, the D. mauritiana Odysseus-H (OdsH) gene causes complete hybrid malesterility only when introgressed into D. simulans along with an additional, distal region of the X chromosome (P erez and W u 1995). In con- trast, our results show that a single, heterozygous in- trogression of the M. guttatus hms1 into a M. nasutus genetic background (i.e., the RSB 3 line) results in
A relatively high level (18%) of spikelet sterility was observed in the control plants due to the excessively high summer temperatures encountered. Growth tem- peratures ≥36°C significantly decrease pollen produc- tion, pollen viability, seed-set, seed yield and harvest index (Prasad et al. 2006). Within treatments there were significant differences in the amounts of seeds set per spikelet between bagged and unbagged spikelets, which suggests the presence of outcrossing or female fertility. Significant variation was observed between varieties in unbagged panicles while the differences in seed set in the bagged panicles were not significant. This confirms the effectiveness of the chemicals in inducing malesterility and that the ovary remained receptive to outcrossing. Similarly, significant variations in seeds per spikelet in bagged and unbagged panicles were observed for the chemicals between the varieties. Complete malesterility was achieved in Dwarf Wonder and KAT 487 at 2 mg/l of E4FO while Kari Mtama required 3 mg/l. This may result from the difference in their panicle morphology because Dwarf Wonder and KAT 487 are semi-compact varieties while Kari Mtama has very loose panicles. This morphological variation, in turn, may affect the impact of surfactants that favour the penetration of gametocides into the plant (Parodi & Gaju 2009). In addition, E4FO and ethrel are known to have systemic activity (Ali et al. 1999; Chakraborty & Devakumar 2006).
Although the mammalian Y chromosome contains few genes, there is no shortage of candidates for contribution to hybrid sperm abnormality. Most genes on the Y are expressed predominantly or exclusively in the testes, and several are known to be essential for male reproduction. These include the testis determinant Sry , spermatogonial proliferation factor Eif2s3y, Zfy2, which regulates meiotic check points, and a clus- ter of multicopy genes on the male-speciﬁc region of the long arm of the Y (MSYq), which are implicated in postmeiotic spermiogenesis (Mazeyrat et al. 2001; Touré et al. 2004; Ferguson et al. 2009; Royo et al. 2010; Vernet et al. 2011). Among the latter group, Sly is required for the maintenance of PMSR and normal sperm differentiation in mice (Cocquet
T HE reduced fertility of hybrids constitutes a major barrier to reproduction between species (Coyne and Orr 2004). When such “hybrid sterility” has a genetic component, this barrier can become permanent and is expected to increase in severity over time. Hybrid sterility tends to evolve faster than hybrid inviability (Coyne and Orr 2004), and in species with XY sex determination, males usually evolve sterility before females (Coyne and Orr 1989), suggesting that hybrid malesterility is often the ﬁrst form of postzygotic isolation to ap- pear. The genetics of hybrid malesterility between nascent species therefore provides a window into the mechanisms of a primary determinant of speciation in the early stages of the process.
is controlled by two contranscribed reading frames orf 138 and Orf B. While Orf 138 is similar to most mitochondrial sterility-inducing genes, orf B codes subunit 8 of ATP- synthase complex (Gray et al., 1998). In a recent study, Wang et al. (2006) characterized the role of mitochondrial open reading frames (ORF’s) in malesterility in rice. They found that E. coli transformed with Orf 79 established cytotoxicity of the Orf 79 gene product. Later on, Orf 79 was over- expressed in a normal, fertile rice line using the CaMV35S promoter and resulted in 750% pollen abortion, whereas female fertility was unaffected by such transgenic expression. They concluded that Qrf 79 encoded a cytotoxic peptide that caused CMS in rice. These and other studies have implicated different mechanisms of mitochondrial impairment in CMS phenotypes, but ultimately the programmed cell death of sporogenous tissue, especially the tapetum, causes pollen sterility. Mitochondria have been found to be involved in interpretation of cell death signals in both animals and plants. Recently Balk and Leaver (2001) showed that in CMS sunflower, the tapetal cells exhibited characteristic features of programmed cell death including the release of cytochrome c, cell condensation, and separation of chromatin into delineated masses and oligonucleosomal cleavage of nuclear DNA. Such characteristics are similar to apoptosis in mammals, except the condensation of nuclei and disintegration of cells into apoptotic bodies. In the case of maize, it was proposed that the urf 13 gene caused malesterility by PCD, characterized by formation of pores in the mitochondrial membrane (Wu and Cheung, 2000). Holden and Sze (1987) proposed that in the presence of the Bm toxin of Bipolais maydis, the mitochondria carrying the urf 13 gene experienced leakage of small ions and, consequently, loss of membrane potential. Tapetal degeneration has been found to be the common feature of such phenomenon in plants like petunia, wheat, sorghum, sunflower and maize (Laser and Lersten, 1972; Schnable and Wise, 1998). Frank and Barr (2003) generalized the term PCD for triggered and orderly death of cells with apoptosis as its specific subtype in animals.
to maximize recombination between them. Gasua-2La (G) is species, whereas many regions are involved in male hy- an An. gambiae s.s. colony originating from females collected brid sterility (Carvajal et al. 1996; True et al. 1996; in Suakoko, Liberia, in 1986, polymorphic for the 2Rb and 2La inversions, and later selected to be a Xag, 2R⫹, 2La, Coyne et al. 1998; Tao et al. 2003a). This suggests that
However, unlike previously described male-sterile over- proliferation mutants with cell fate defects (Gonczy et al., 1997; Kiger et al., 2000; Matunis et al., 1997; Tulina and Matunis, 2001), the majority of the myt1 mutant cysts do not undergo such ectopic mitotic divisions. Collectively, these data suggest that Myt1 serves distinct Cdk1 regulatory functions that coordinate cell cycle behavior with important developmental transitions. Precisely how Myt1 accomplishes these diverse functions is unknown; however, our results are consistent with the idea that Myt1 specifically regulates Cdk1 activity in the cytoplasm (Liu et al., 1997; Wells et al., 1999). Strikingly, RNAi depletion of Myt1 in cultured Drosophila cells was previously reported to cause a marked disruption of the Golgi apparatus (Cornwell et al., 2002). This observation suggests an intriguing possibility. As the Golgi apparatus serves a key role in trafficking and secretion of proteins in rapidly growing cells, perhaps Myt1 regulation of Cdk1 activity might indirectly affect the biosynthesis and assembly of subcellular structures required for crucial developmental transitions affected in myt1 mutants.
Chopra V. L. 2001. Expression of malesterility in alloplasmic Brassica juncea with Erucastrum canariense cytoplasm and development of a system for fertility restoration. Plant Breed., 120 : 479-482. Rao, G.U. and Shivanna, K.R. 1996. Development of a
Results are given of genetic studies of malesterility using plants from two natural populations from Sussex, England. Both populations have substantial frequencies of females, z0.25 in population 1 and 0.60 in population 3. As in the few other gynodioecious populations studied in detail, many genetic factors are present. In population 1, there are at least two, and more likely three, different cytoplasmic types, one of which appears to produce malesterility in progeny from any hermaphrodite pollen donor; in other words restorer alleles for this cytoplasm are rare or absent from the population. The other two populations can be carried in hermaphrodites that have the dominant restorers. In population 1, there are also probably three restorer loci with complementary recessive male-sterility alleles, as well as a locus with duplicate action, which cannot produce malesterility unless the plant is also homozygous for the recessive allele at another locus. The results from population 3 are quite similar, though there was no evidence in this population for an unrestored sterility cytoplasm. A similar joint nucleocytoplasmic model with multiple restorers fits data from Thymus vulgaris.