Haploidy and aneuploidy in switchgrass mediated by misexpression of CENH3

Plant chromosome engineering - past, present and future

Spontaneous chromosomal rearrangements (CRs) play an essential role in speciation, genome evolution and crop domestication. To be able to use the potential of CRs for breeding, plant chromosome engineering was initiated by fragmenting chromosomes by X-ray irradiation. With the rise of the CRISPR/Cas system, it became possible to induce double-strand breaks (DSBs) in a highly efficient manner at will at any chromosomal position. This has enabled a completely new level of predesigned chromosome engineering. The genetic linkage between specific genes can be broken by inducing chromosomal translocations. Natural inversions, which suppress genetic exchange, can be reverted for breeding. In addition, various approaches for constructing minichromosomes by downsizing regular standard A or supernumerary B chromosomes, which could serve as future vectors in plant biotechnology, have been developed. Recently, a functional synthetic centromere could be constructed. Also, different ways of genome haploidization have been set up, some based on centromere manipulations. In the future, we expect to see even more complex rearrangements, which can be combined with previously developed engineering technologies such as recombinases. Chromosome engineering might help to redefine genetic linkage groups, change the number of chromosomes, stack beneficial genes on mini cargo chromosomes, or set up genetic isolation to avoid outcrossing.

Accelerated Breeding for Helianthus annuus (Sunflower) through Doubled Haploidy: An Insight on Past and Future Prospects in the Era of Genome Editing

The aim of any breeding process is to fully express the targeted, superior/desirable parent characteristic in the progeny. Hybrids are often used in this dynamic, and complex process for which homozygous parents-which may require up to eight generations of back crossing and selection-are required. Doubled haploid (DH) technologies can facilitate the production of true breeding lines faster and in a more efficient manner than the traditional back crossing and selection strategies. Sunflower is the third most important oilseed crop in the world and has no available double haploid induction procedure/technique that can be efficiently used in breeding programs. A reproducible and efficient doubled haploid induction method would be a valuable tool in accelerating the breeding of new elite sunflower varieties. Although several attempts have been made, the establishment of a sunflower doubled haploid induction protocol has remained a challenge owing recalcitrance to in vitro culture regeneration. Approaches for haploid development in other crops are often cultivar specific, difficult to reproduce, and rely on available tissue culture protocols-which on their own are also cultivar and/or species specific. As an out-crossing crop, the lack of a double haploid system limits sunflower breeding and associated improvement processes, thereby delaying new hybrid and trait developments. Significant molecular advances targeting genes, such as the centromeric histone 3 (CenH3) and Matrilineal (MTL) gene with CRISPR/Cas9, and the successful use of viral vectors for the delivery of CRISPR/Cas9 components into plant cells eliminating the in vitro culture bottleneck, have the potential to improve double haploid technology in sunflower. In this review, the different strategies, their challenges, and opportunities for achieving doubled haploids in sunflower are explored.

Creating novel ornamentals via new strategies in the era of genome editing

Ornamental breeding has traditionally focused on improving novelty, yield, quality, and resistance to biotic or abiotic stress. However, achieving these goals has often required laborious crossbreeding, while precise breeding techniques have been underutilized. Fortunately, recent advancements in plant genome sequencing and editing technology have opened up exciting new frontiers for revolutionizing ornamental breeding. In this review, we provide an overview of the current state of ornamental transgenic breeding and propose four promising breeding strategies that have already proven successful in crop breeding and could be adapted for ornamental breeding with the help of genome editing. These strategies include recombination manipulation, haploid inducer creation, clonal seed production, and reverse breeding. We also discuss in detail the research progress, application status, and feasibility of each of these tactics.