Hybrid Embryo Abortion Research Articles

Transcriptome Analysis Reveals the Role of Phytohormones in the Distant Hybridization of Peony Embryo Abortion

Peonies are significant ornamental plants that are primarily propagated through distant cross-breeding to create new varieties. However, hybrid failure is a critical issue that impedes the advancement of breeding. Numerous studies have demonstrated that endogenous hormones in the seed embryo constitute a significant factor in embryo failure. Nevertheless, it is still unknown how plant hormones control the development of peony embryos at the molecular level. In this study, we characterized the endogenous hormone levels in peony seeds of hybrid-aborted, hybrid-normal, and self-crossing normal after 26 days of pollination (DAP). Our findings show that the hybrid-aborted embryos had significantly higher amounts of ABA, IAA, and GA. In addition, the ratio of GA+IAA/ABA was lower than that of the hybrid-normal seeds and higher than that of the self-crossing normal seeds. To further investigate the mechanism of hormone control on peony embryo development, we conducted a transcriptome sequencing analysis of the three seed types. Results revealed that differentially expressed genes involved in phytohormone metabolism and signal transduction significantly enriched the aborted embryos. Furthermore, we examined the expression levels of six hormones in different seeds and used the Gene Common Expression Trend analysis to analyze genes highly correlated with phytohormone in the KEGG pathway. We used protein interaction networks to explore the interactions between proteins in the hormone pathway in aborted embryos. Then we identified key genes and transcription factors (TFs) such as Abscisic acid-insensitive 5 (ABI5), Auxin Response Factor 5 (ARF5), Gibberellin Insensitive Dwarf 1 (GID1), Arabidopsis Response Regulator4 (ARR4), Jasmonate-zim-domain protein 1 (JAZ1), Brassinazole-resistant 1 (BZR1), etc., whose functions require further investigation. Our findings establish a foundation for the metabolic regulation of peony hybrid embryo abortion via networks regulating phytohormone signaling. However, further research is needed to determine the exact mechanisms by which hormones regulate peony embryo development and to explore new methods for improving the success rate of hybridization.

Analysis of incompatibility barriers during cross-pollinations among <i>Phaseolus</i> L. and other leguminous plants

Plant breeding is intended to seek for ways of realizing a genetic structure adapted to criteria and population needs. In this context, cross-pollinations are for great interest. They offer the means of creating a wide genotypic variability. However, a limited number of species are able to undergo hybridization studies. In Phaseolus L., improvement can be envisioned by either exploiting the primary genetic pool of the species, or the genetic variability of other species. In fact, there are wild or wild-like species more resistant to stresses or diseases than the cultivated ones. The methods of embryo rescues facilitate the interspecific crosses and contribute to exploiting the available genetic diversity within plant germplasm. Difficulties related to obtaining hybrids in grain legumes, and Phaseolus L. in particular, are reported in this research. It is possible to avoid the incompatibility barriers based on their appearance time. When they are pre-zygotic, the use of growth regulators during pollination is recommended. The in vitro explants culture is the most usual method to overcome the post-zygotic barriers. The mechanisms leading to abortion of hybrid embryos, as well as adequate methods to overcome the interspecific incompatibilities should be subjected to further studies.Keywords: Abortion, hybridization, interspecific barriers, Phaseolus L., plant embryos.

Embryonic Development and Changes of Endogenous Hormones in Interspecific Hybrids between Peanut (A. hypogaea L.) and Wild Arachis Species

The peanut cultivar Yuhua 15 was used as female parent to cross with wild species A. correntina and A. macedoi, re- spectively, with intervarietal cross Yuhua 15×Baisha 1016 as check. There were no significant differences observed in pegging percentage among all the crosses. It indicated normal fertilization in the interspecific crosses. Embryo development was observed through paraffin sections, and contents of endogenous hormones including IAA, GA 3 , ZR+DHZR, and ABA in the developing embryos of hybrids were determined with ELISA. In comparison with normal seed development of Yuhua 15×Baisha 1016 and Yuhua 15×A. correntina, Yuhua 15×A. macedoi was incompatible due to a deterred embryo development at approximately 12–17 days after pollination followed by the hyperplasia of integument into the embryo sac which suppressed further development of the embryo and finally resulted in abortion. Compared with two compatible crosses, the ABA content and ratios of ABA to total of other auxin in developing embryos of cross (Yuhua 15×A. macedoi) were relatively higher at the early development stage, while the contents of IAA, GA 3 , and ZR+DHZR remained at a relatively lower level, which speculates on that abnormal hormone ac- tivities may be an important reason leading to the abortion of hybrid embryos. Peg bases of Yuhua 15×A. macedoi were treated with IAA, KT, or mixture of the two, showing that the exogenous hormones can increase the length of ovule.

Interspecific hybridization by embryo rescue in the genus Cyclamen

Numerous cultivars of cyclamen have been developed by improving wild plants of Cyclamen persicum, and they are now among the most important pot plants. However, no cultivars have yet been produced in the other 21 Cyclamen species. Furthermore, these 21 wild species have not yet been used for improving C. persicum cultivars due to hybrid inviability and hybrid sterility. In recent studies, hybrid inviability caused by abortion of hybrid embryos was overcome by an embryo rescue technique involving culture of ovules with placenta, which resulted in the production of interspecific hybrids between C. persicum and each of ten wild species. Hybrid sterility caused by abnormal meiotic chromosome behavior in hybrids (allodiploids) between diploid C. persicum and each of two diploid wild species was overcome by chromosome doubling using in vitro colchicine treatment, resulting in the production of two types of fertile amphidiploids (allotetraploids). On the other hand, three types of allotetraploids were produced between autotetraploid cultivars of C. persicum and each of three autotetraploid wild species by the embryo rescue technique without chromosome doubling. Embryo rescue and in vitro chromosome doubling are simple and useful methods for overcoming hybrid inviability and hybrid sterility in interspecific hybridization in the genus Cyclamen. Some of the fertile amphidiploids thus produced have already been incorporated into commercial breeding of novel types of cyclamens with important traits such as flower fragrance and disease resistance.

Intergeneric hybridization between Brassica species and Crambe abyssinica

In crosses of B. napus × C. abyssinica and B. campestris × C. abyssinica, pre-fertilization incompatibility was observed. In crosses of B. juncea × C. abyssinica, pollen grains of C. abyssinica were compatible to the stigmas of all the B. juncea pistils, the pollen tube growth was normal and the pollen tube reached the micropyle in 3–4 days after pollination. Through comparative studies on embryo development in intergeneric crosses of B. juncea × C. abyssinica and self-pollination of B. juncea, the causes of the hybrid embryo abortion were found. An intergeneric hybrid between B. juncea × C. abyssinica was obtained for the first time through conventional crossing method combined with ovary culture, when C. abyssinica was used as a paternal parent. The hybridity was confirmed by morphology, cytology and isozyme analysis.

Genetical aspects of hybrid embryo abortion in the genus Lens L.

Hybrid embryo abortion is an effective crossing barrier in the genus Lens L. It divides the genus into two crossing groups: the Culinaris and the Nigricans groups; but it is also evolving within the Culinaris group. The abortion of the F1 embryo is strongly affected by dominant gene action. In the segregating generations embryo abortion is of a quantitative nature and has both components, dominant and additive. These were expressed differentially in the Lens ervoides × L. culinaris and L. orientalis × L. culinaris cross combinations. The genetic control of embryo abortion was indicated further by the association between marker loci and embryo abortion rates in segregating generations. Embryo abortion was not associated with chromosomal aberrations. The establishment of an embryo abortion reproductive barrier by a single somatic mutation in a locus affecting seed development is proposed as a first step in a build-up of genetic isolation in the genus Lens.

Wild Lentils

Abstract Wild lentils are potential genetic resources for the cultivated lentil, Lens culinaris ssp. culinaris. Their actual value for crop improvement depends on their genetic relationships with the cultigen and their diversity for traits of economic importance. The current view on Lens taxonomy and the latest information on geographic distribution and ecology of the wild taxa are reviewed. The latter is essential for successful collection of wild lentils in their natural habitats. Intraspecific variation is extensively reviewed and evidence for cryptic speciation has been indicated. Crossability potential divides the genus into two groups: L. culinaris — L. odemensis and L. ervoides — L. nigricans. Crosses between members of different group fail because of hybrid embryo abortion. Using embryo culture, viable hybrids can be obtained between L. ervoides and members of the other group. Of the wild lentils, the putative ancestor of the cultigen, L. culinaris ssp. orientalis, is a member of the crop's primary gene pool, whereas L. odemensis and L. ervoides constitute the secondary gene pool. Morphological, physiological, and genetic attributes of ssp. orientalis have been used to assess the process of lentil domestication. It has been pointed out that elimination of seed dormancy was a necessary step for successful lentil cultivation, and that the dormancy-free type probably evolved in wild stands by the aid of selection pressure exerted by man.

Anatomical Aspects of Hybrid Embryo Abortion in the Genus Lens L.

Hybrid embryo abortion at about 14 days after pollination (DAP) is typical of crosses between the cultivated lentil, Lens culinaris, and the wild species L. ervoides, regardless of the direction of the cross. Hybrid embryo abortion was also observed in crosses between the cultivated lentil and specific accessions of its wild progenitor, L. orientalis, and between these accessions and L. ervoides. The embryos of the parental lines of these three taxa reached the globular stage ca. 5 DAP; the cotyledons, shoot, and root primordia were observed ca. 10 DAP, and the immature seeds reached their final size ca. 14 DAP. The embryos were surrounded by a thin layer of endosperm that disappeared when the immature seeds reached their final size. The development of the hybrid embryos and endosperm was similar to that of the parental lines up to the globular stage; after this stage retarded development and progressive necrosis were detected. At 14 DAP the hybrid embryos contained smaller cotyledons, initiations of shoo...

Zygotic Polyembryony in Interspecific Hybrids of Carica papaya and C. cauliflora

Abstract A study of reproductive barriers limiting interspecific hybridization between Carica papaya L. and C. cauliflora Jacq. was undertaken in four reciprocal interspecific crosses using two different lines of each species. Particular attention was focused on determining whether polyembryonic clusters produced in these crosses were of maternal or zygotic origin. Prezygotic barriers were unimportant; pollen tube penetration and zygote formation were similar in intra- and interspecific crosses. Substantial postzygotic disruptions were observed, including disorganized growth and abortion of hybrid embryos and lack of normal endosperm development. In most crosses, disorganized embryos aborted before differentiating into polyembryonic structures. However, crosses employing UH345 (C. cauliflora) as female parent produced some embryos that developed to maturity (6 months), and, in these crosses, embryogenic proliferation from zygotic tissue became evident as early as the beginning of the 3rd month. There was no evidence of somatic embryogenesis from maternal tissues in any cross. Embryos rescued 3 to 6 months after pollination continued embryogenic growth in vitro on basal Murashige and Skoog (MS) medium and germinated on medium containing 0.2 mg BA/liter and 0.5 mg NAA/liter. Zymograms assayed for isocitrate dehydrogenase, malate dehydrogenase, and phosphoglucomutase activity confirmed the zygotic origin of tissues taken from in vitro cultures and recovered plantlets. Vigor, viability, and fertility (< 1% stainable pollen) of hybrids recovered from embryo culture were low. Chemical names used: 6-benzylaminopurine (BA); 1-napthaleneacetic acid (NAA).