MALE STERILITY OF CROP
Cotton has significant heterosis. Hybrid cotton usually can increase production in lint yield by about 15% compared with conventional self-pollinated cultivars, and also can get obvious improvement in fiber quality, disease resistance, insect resistance, adversity resistance and photosynthetic efficiency. Among some links of cotton heterosis use, the most important link is the castration in the production of hybrid seeds. At present, there are four ways for the castration, such as hand emasculation, chemical male gametocide, nuclear male sterility and cytoplasmic male sterility (CMS). The production practice showed that use of cotton male sterility could not only simplify the hybrid seed production but also save the production cost on a commercial economic scale. In particular, the way of hybrid seed production by use of cotton CMS line, maintainer line and restorer line were the most effective way since it could overcome some disadvantages in the other ways. Therefore, in this paper, the study and application of the cotton CMS system in hybrid seed production were overviewed and some of problems currently limiting application were also addressed. At first, the genetic, cytological and biochemical characteristics of the cotton CMS were reviewed. Secondly, the positive/negative effects of sterile cytoplasm in hybrid F1 were analyzed, and how to overcome these negative effects, such as pollen temperature sensitive and F1 not expressing complete fertility, by developing strong restorer lines with a stronger ability for F1 fertility restoration, was discussed in detail. For an example, transgenic strong restorer line could be developed by introducing the exogenous GST gene, which was assumed to have the function of enhancing pollen vitality, into some conventional restorer lines, and so that hybrids with higher heterosis could be produced by crossing this strong restorer with sterile lines. According to the characteristics of cotton as an often cross-pollination crop, this paper recommended in detail the key techniques of hybrid cotton seed production, such as rules of parent (sterile line and restorer line) selection, location selection and environment optimization for enriching native pollinators to produce more hybrid seeds. Then, the paper pointed out that compared with other crops, cotton hybrid seed production based on CMS system has four advantages in the cotton heterosis use: (1) The purity of hybrid seeds can be guaranteed because there is no pollen in anthers of cotton CMS line and its sterility is very stable and not affected by the climate and other environments; (2) The high yield of hybrid seed can be obtained since the long flowering period (about 3 months) of cotton does not result in the flowering asynchronism between sterile line and restorer line; (3) The wide ecological adaptability of cotton and the possibility of large-scale hybrid seed production will be benefited to popularize hybrid cotton; and (4) Interspecific heterosis between upland cotton (Gossypium hirsutum L.) and sea-island cotton (G. barbadense L.) can be used. It is predicted that the hybrid cotton production based on CMS system will be the main approach to utilize heterosis of cotton. Finally, the future works in study and application of CMS in cotton heterosis, especially in development of new sterile lines and restorer lines by use of modern biotechnology, was also discussed.
Safe and effective F1 seed production method is the key to hybrid production in rapeseed. Father parent lines with tribenuron-methyl resistance (or tolerance) and self-incompatiblity can be developed by means of backcross breeding. In the F1 hybrid seed production by using tribenuron-methyl as the male sterility induction agent, the father parent lines have no seedset by self-pollination because of their self-incompatibility, and are not affected by the chemical agent because of their tribenuron-methyl resistance (or tolerance). Therefore, the parental lines can be mixed sowing and the seeds can be mixed harvesting. Using the method we proposed, if the lines with tribenuron-methyl resistance (tolerance) and self-incompatiblity are already developed, hybrid breeding can be carried out immediately. It saves labor costs, improves seed production efficiency and increases seed purity because of the mixed sowing and mixed harvesting.
【Objective】To study the differences in female fertility of RN-type soybean cytoplasmic male sterile lines (A-lines) and maintainer lines (B-lines), determine whether there is a decline in female fertility in RN-type soybean cytoplasmic male sterility lines, and explore the correlation between female fertility and outcrossing rate in male sterile lines. 【Method】 Firstly, 6 pairs of sterile lines and maintainer lines were selected from more than 200 RN-type cytoplasmic male sterile lines; outcrossing rates among these lines were different. Second, the outcrossing rate of male sterile lines was evaluated using honeybee pollination in net cages. Third, six male sterile lines were pollinated by non-removing stamen test, with male parents of the same restorer line, to determine whether there were differences in fertilization and podding. Finally, the differences in survival rate between sterile lines and maintainer lines were studied by removing stamens and non-removing stamens parallel cross test with the same restorer line used as the male parent. 【Result】 The outcrossing rates in cages were significantly different among the six sterile lines tested: the highest outcrossing rate was 49.46% and the lowest outcrossing rate was 15.94%. there were significant differences among survival rates of artificial crosses of six sterile lines tested: the survival rate of sterile lines with a high outcrossing rate were significantly higher than that of medium and low outcrossing rate sterile lines and the survival rate of sterile lines with medium outcrossing rate were significantly higher than that of low outcrossing rate sterile lines. For crossing survival rate after artificially removing stamens, A-lines with high and medium outcrossing rates were significantly higher than that with low outcrossing rates; there were no significant differences among B-lines with high, medium, or low outcrossing rates; there were no significant differences among high A-lines, middle A-lines, and their corresponding B-lines, while A-lines with a low outcrossing rate were significantly lower than their corresponding B-lines. For crossing survival rate by artificially not removing stamen, A-lines with a high outcrossing rate were significantly higher than that with medium or low outcrossing rates; there were no significant differences among B-lines with high, medium and low outcrossing rates; there were no significant differences among high A-lines, middle A-lines, and their corresponding B-lines, while A-lines with low outcrossing rate were significantly lower than their corresponding B-lines. 【Conclusion】 For RN-type cytoplasmic male-sterile lines of soybean, female fertility of A-lines with high outcrossing rates were normal and female fertility of a few A-lines with low outcrossing rates were poor, affecting their seed setting. Female fertility of B-lines with different outcrossing rates were all normal, the outcrossing rate of A-lines in cages were significantly positively correlated with their crossing survival rate following artificial stamen removal and in plants where the stamen was not removed, the outcrossing rates of A-lines in cages were not correlated with their B-lines’ crossing survival rate. All parallel crosses by removing and non-removing stamens can thus be used to evaluate female fertility of A-lines.
【Objective】It is one of the most efficient ways to utilize cytoplasmic male sterile (CMS) lines in hybrid seed production, which could improve the purity of seeds, reduce the cost in creating hybrid seeds and enhance the competitiveness of Chinese seed companies. The comparative transcriptome analysis of the anthers at different development stages from the CMS line, the maintainer line and the restorer line (the three lines) were performed in order to understand the mechanism of sterility and restoration of CMS-C in maize, and also to elucidate the regulation network between the restorer gene and the sterile gene, which will provide the fundamental basis for the employment of maize CMS in hybrid seed production.【Method】The transcriptome sequencing was carried out on the anthers at the prophaseⅠ, the metaphaseⅠand the tetrad stage from the three lines based on the elite inbred line Yu87-1. Method of comparative analysis was used to deal with all the transcripts by the tools such as hisat2, ballgown and DESeq2, and to predict genes involved in the regulation network between the sterile gene and the restorer gene, between the different development stages and through the development time series. qRT-PCR was used to verify the differentially expressed genes. The activity of ATPase was quantified with by the spectrophotometric method for the verification of the putative hypothesis.【Result】Transcriptome sequencing totally produced 156.59 Gb sequence data. After mapping and assembling, 53035 Unigenes were obtained. A total of 5676 differentially expressed (DE) genes were identified from the pairwise comparisons (except for comparisons between the restorer lines and the maintainer lines) in the anthers at the different stages from the three lines. Of those, 4705 DE genes between the comparisons of the development stages, 2693 DE genes between the comparisons of the different lines and 135 DE genes related to the time series. The GO molecular functional analysis showed that the genes related to ATP binding, DNA binding and zinc ion binding were highly enriched, in cell component analysis, genes located in integral component of membrane, nucleus and plasma membrane were enriched, and in biological process, genes involved in DNA-templated transcription, regulation of transcription, oxidation-reduction process and primary metabolic process were enriched. KEGG pathway analysis indicated that the oxidative phosphorylation pathways, the carbon metabolism pathways and glycolysis pathways were mostly enriched. Compared to the maintainer lines, several genes involving in the oxidative phosphorylation pathways were significantly down-regulated in the sterile lines, while those down-regulated genes were recovered, besides other genes in the same pathways were also coordinately regulated. The expression trend determined by qRT-PCR on the selected DE genes was in accordance with that in the transcriptome data. The enzyme activity results show that the activity of ATPase in the sterile line was greatly reduced compared to the maintainer line, while in the restorer line, the activities the ATPase were restored due to the existence of the restorer gene.【Conclusion】 The onset of the changes in the gene expression caused by the sterile gene in the anthers of CMS-C maize may happen after metaphaseⅠ and before telophase Ⅱ in meiosis before visible phenotype occurred. The energy deficiency model may account for the mechanism of the sterility in maize CMS-C, and the energy requirements were compensated by the restorer gene through direct or indirect manner.
【Background】 Plant pollen is surrounded by pollen wall which acts as a natural protective barrier for male gametes and plays a pivotal role in plant reproductive development. The main component of pollen wall is sporopollenin, which is mainly composed of lipidic and phenolic substances. Therefore, the metabolism of these two substances is a key step for anther wall and pollen wall formation. PKS1/PKSA/LAP6 and PKS2/PKSB/LAP5 show conserved biochemical functions in sporopollenin biosynthesis pathways among different species. 【Objective】 The role of OsPKS1 and OsPKS2 in rice anther wall and pollen wall development was studied to provide a new understanding for the mechanism of this process. 【Method】 A gene co-expressed network, AntherNet predicted a gene OsPKS1 that might be involved in sporopollenin biosynthesis, using the CRISPR/Cas9 genome editing system to generate ospks1 and ospks1 ospks2 in Japonica subspecies 9522 background and ospks2 background, respectively. Under the same growth condition, the vegetative growth and floral organ development of the mutant plants were analyzed by comparing the phenotypes of the wild type and the mutants. I2-KI staining was utilized to analyze the pollen viability of ospks1 and ospks1 ospks2. Semi-thin section was performed to observe four cell layers and microspore development in the wild type and the mutants at different stages. Scanning electron microscope (SEM) was used to observe the fine structures of anther wall outer and inner surface as well as pollen wall surface both in the wild type and the mutants. And transmission electron microscopy (TEM) was performed to observe the fine structures of anther wall cell, Ubisch body and pollen wall of the wild type and the mutants.【Result】Four ospks1 and four ospks1 ospks2 were obtained by CRISPR/Cas9 approach, among which ospks1-3 and ospks1-4 ospks2 were homozygous mutants. Both ospks1-3 and ospks1-4 ospks2 were male sterile. ospks1-3 and ospks2 displayed abnormal pollen wall and Ubisch body, however, the detailed morphology was different between two mutants. ospks1-3 could form convex wall structure on the surface of pollen wall and the tapetal layer could be normally degraded; a large number of tiny cavities were formed in the inner structure of pollen wall and the bacula became shorter, which might cause invalid connection between tectum and nexine; the bottom structure of Ubisch bodies was decreased while the top structure was increased and Ubisch bodies were sharper than those of the wild type. By observing ospks1-4 ospks2, it was found that the cuticle was reduced and the tapetal layer could not be degraded normally. Besides, there was no obvious pollen wall structure on the surface of microspores and the microspores were degraded at stage 11; Ubisch bodies were less formed with abnormal structure at stage 9 and were detached from the anther wall at stage 11. 【Conclusion】 The function of PKS1/PKSA/LAP6 and PKS2/PKSB/LAP5 are conserved among various species and could affect the biosynthesis and accumulation of sporopollenin. However, these two genes show different function for the formation of the inner structure of pollen wall and Ubisch bodies in rice: OsPKS1 is more important for the formation of bacula and the bottom structure of Ubisch bodies; OsPKS2 is more important for the formation of tectum and the top structure of Ubisch bodies. They regulate the formation of pollen wall, anther wall and the degradation of tapetum.
