Genomic Instability in Somatic Hybridization between Poncirus and Citrus Species Aiming to Create New Rootstocks

Abstract

Rootstocks are an important component for citrus adaptation to increasing biotic and abiotic stresses resulting from global climate change. There is a strong complementarity between Citrus species, which adapt to abiotic stresses, and Poncirus trifoliata and its intergeneric hybrids, which exhibit resistances or tolerances to major diseases and pests. Thus, symmetrical somatic hybridization between complementary diploid rootstocks of these two genera appears to be an efficient way to develop new tetraploid rootstocks in order to address the new challenges of the citrus industry. New intergeneric somatic hybrids were obtained by electrofusion between protoplasts of Citrus and P. trifoliata hybrids. Extensive characterization of the nuclear and cytoplasmic genomes was performed by genotyping-by-sequencing (GBS) analysis. This revealed diploid cybrids and nuclear somatic hybrids. Mitochondrial genomes were mostly inherited from the callus parent, but homologous recombination events were observed for one parental combination. Chloroplasts exhibited random uniparental inheritance. GBS revealed local chromosomal instabilities for all nuclear somatic hybrids and whole chromosome eliminations for two hybrids. However, at the whole genome level, symmetrical addition of the nuclear genomes of both parents was predominant and all somatic hybrids displayed at least one trifoliate orange haplotype throughout the genome.

Inheritance pattern of tetraploids pummelo, mandarin, and their interspecific hybrid sour orange is highly influenced by their phylogenomic structure

“…Protoplast fusion is another technique used to create tetraploid somatic hybrids, theoretically adding dominant characters of both diploid parental genomes without sexual recombination (Grosser et al, 2000;Ollitrault et al, 2007;Dambier et al, 2011;Grosser and Gmitter, 2011). However, recent studies have revealed some chromosome instability and loss or duplication of substantial genomic regions (Ruiz et al, 2018;Dambier et al, 2022). These methods have been used for citrus rootstock breeding producing a wide range of tetraploid germplasm at intraspecific, interspecific, and even intergeneric levels.…”

Advance in Cell Cultures, Cell Fusion and Cell Splitting of Medicinal and Edible Plant

“…Somatic hybridization has a significant advantage in citrus improvement because citrus plants could regenerate into whole plants [115]. Researchers were initially focused on produce male sterile and seedless citrus cybrids then tried more explorations of somatic hybridization covering improvement of techniques, citrus species, rootstocks resistance and so on [116][117][118][119]. Hybrid of somatic embryos between citrus and murraya puniculata were obtained by electrofusion, and further study revealed that percentage of multinucleated protoplast increasing linearly with increase the alternating voltage [117].…”

“…Aiming to develop new tetraploid rootstocks harboring virtues of both parents, new intergeneric somatic hybrids were obtained by electrofusion between protoplasts of citrus, which adapt to abiotic stresses, and P. trifoliata hybrids, which exhibit resistances or tolerances to major diseases. Diploid cybrids and nuclear somatic hybrids were found, while symmetrical addition of the nuclear genomes of both parents was predominant at the whole genome level [118]. Asymmetrical somatic hybridization between two complementary diploid parents are thought be an efficient way to develop new tetraploid rootstocks for citrus stress adaptation [117][118][119].…”

“…Diploid cybrids and nuclear somatic hybrids were found, while symmetrical addition of the nuclear genomes of both parents was predominant at the whole genome level [118]. Asymmetrical somatic hybridization between two complementary diploid parents are thought be an efficient way to develop new tetraploid rootstocks for citrus stress adaptation [117][118][119].…”

Meiotic Behaviors of Allotetraploid Citrus Drive the Interspecific Recombination Landscape, the Genetic Structures, and Traits Inheritance in Tetrazyg Progenies Aiming to Select New Rootstocks

“…Several teams have widely used somatic hybridization to create tetraploid rootstocks combining characters of interest from different genetic resources. This method allows researchers to add genomes of two diploid genotypes without sexual recombination [42][43][44][45][46][47][48][49] and, therefore, to combine favorable dominant traits of the two parents. Recent genomic studies revealed chromosome instability in somatic hybrids, which can lead to substantial loss of genomic regions of parental lines [42].…”