Genetic characteristics and ploidy trigger the high inducibility of double haploid (DH) inducer in Brassica napus

Abstract

Background Our recently reported doubled haploid (DH) induction lines e.g., Y3380 and Y3560 are allo-octoploid (AAAACCCC, 2n = 8× ≈ 76), which can induce the maternal parent to produce DH individuals. Whether this induction process is related to the production of aneuploid gametes form male parent and genetic characteristics of the male parent has not been reported yet. Results Somatic chromosome counts of DH inducer parents, female wax-less parent (W1A) and their F1 hybrid individuals revealed the reliability of flow cytometry analysis. Y3560 has normal chromosome behavior in metaphase I and anaphase I, but chromosome division was not synchronized in the tetrad period. Individual phenotypic identification and flow cytometric fluorescence measurement of F1 individual and parents revealed that DH individuals can be distinguished on the basis of waxiness trait. The results of phenotypic identification and flow cytometry can identify the homozygotes or heterozygotes of F1 generation individuals. The data of SNP genotyping coupled with phenotypic waxiness trait revealed that the genetic distance between W1A and F1 homozygotes were smaller as compared to their heterozygotes. It was found that compared with allo-octoploids, aneuploidy from allo-octoploid segregation did not significantly increase the DH induction rate, but reduced male infiltration rate and heterozygous site rate of induced F1 generation. The ploidy, SNP genotyping and flow cytometry results cumulatively shows that DH induction is attributed to the key genes regulation from the parents of Y3560 and Y3380, which significantly increase the induction efficiency as compared to ploidy. Conclusion Based on our findings, we hypothesize that genetic characteristics and aneuploidy play an important role in the induction of DH individuals in Brassca napus, and the induction process has been explored. It provides an important insight for us to locate and clone the genes that regulate the inducibility in the later stage.

Rapid Creation of Interspecific Hybrid Progeny to Broaden Genetic Distance through Double Haploid (DH) Inducer in Brassica napus

“…The induced F 1 by interspecies hybridization was obtained by induction selfing through F 1 egg cells [ 21 , 22 ], and there might be changes in the number of chromosomes and ploidy changes. Through the analysis of the ploidy of T19-4 and T19-5, T19-4 and T19-5 were mostly triploid (excluding two pseudohybrid).…”

“…Through cytological identification and FISH observation, it was found that hexaploid plants have about 54 chromosomes (2n = 6x ≈ 54, AAACCC) ( Figure 4 d), analyzing the source of hexaploid plants. Since the octoploid DH inducer was prone to producing aneuploid gametes [ 22 , 27 ], it was basically determined that it was the interspecific hybrid F 1 and the octaploid DH inducer hybridized which lost three A chromosomes. It was inferred that the octoploid plants in W59 were also interspecific crosses between F 1 and octoploid DH induction lines.…”

“…By studying the characteristics of octoploid induction system materials, it was found that octoploids were genetically unstable [ 27 , 31 ], prone to producing aneuploid gametes, and prone to mixed ploidy [ 22 , 27 , 31 ]. Combining the genesis mechanism of maize haploid induction line [ 32 ], it was found that the DH induction lines together determine the high inducibility due to genetic characteristics and ploidy [ 22 ]. At the same time, it was also found that a large number of aneuploid gametes appeared in triploid pollen.…”

“…At the same time, it was also found that a large number of aneuploid gametes appeared in triploid pollen. T19-4 and T19-5 could induce induction, which also provides a reference for other species to develop an induction phenomenon [ 22 ]. In this study, the selfing rate of triploid pollen was very low, and it did not induce its own egg cells.…”

“…To describe the characteristics of the induction material more accurately, this method was named the double haploid (DH) inducer, e.g., Y3560 and Y3380 in B. napus , referred to as DH induction line (DH inducer). Through the observation of the induction phenomenon, the phenotype of the offspring, and the detection of SNP chip, it was speculated that the induction process was due to the zygotes produced by the inducible sperm cells and the maternal parent eggs, the paternal chromosome being eliminated during the mitosis of the zygote, and then the maternal chromosome doubling and forming DH offspring [ 21 , 22 ]. Can use of DH inducer pollen instead of interspecific F 1 continuous backcrossing with the parent to double the chromosomes of interspecific F 1 egg cells form induced offspring with genetic diversity?…”