S01 - Session P2 - Chromosomal re-arrangement detected on chromosome 4 in a novel bud sport of 'Beni-hakuto'; Japanese peach with multiple mutant phenotypes

Authors: Ryohei Nakano *, Takashi Kawai, Daisuke Takata, Yuki Taniguchi, Takayuki Tamura, Mamoru Sato, Kazusa Nishimura, Ko Motoki, Akira Yamazaki, Tetsuya Nakazaki, Fumio Fukuda, Koichiro Ushijima

'Akatsuki' is the most produced Japanese peach in Japan and used in many breeding programs. 'Beni-hakuto' is a bud sport (somaclonal mutatnt) of 'Akatsuki' and now a novel bud sport of 'Beni-hakuto' has been found in a grower's orchard. This mutant showed differences in multiple traits regarding fruit development and quality from the original 'Beni-hakuto'. Growth curves of fruit borne on the mutant branch showed a longer period of slow growth (stage II) than those borne on the original 'Beni-hakuto' branch. As a result, fruit on the mutant branch reached harvest maturity about 3 weeks later than those on the original branch. Enhanced incidences of fruit drop, abnormal fruit shape and split pit were also observed on the mutant branch. Reddish pulp and/or water-soaked brown flesh were shown in most of the harvested mutant fruit. DNA-seq analysis to compare the mutant genomic sequence with that of the original 'Beni-hakuto' detected a 13.3 Mbp region with LOH (loss of heterozygosity) hot spots at the upper arm of chromosome 4 and was designated LOH-region. No obvious copy number variants were found in this LOH-region. These results indicated the occurrence of deletion and duplication events on chromosomal segments corresponding to the LOH-region. It was hypothesised that the double strand breakdown occurred at 13.3 Mbp of one of the two chromatids of chromosome 4 of 'Beni-hakuto' and then the upper segment was lost. The deleted region could be repaired by homologous recombination instead of non-homologous end-joining, which in turn, led to creating the LOH-region and unmasking the recessive phenotypes in the mutant. It has been reported that the 13.3 Mbp genomic region contains several important loci regulating fruit development, quality and postharvest properties in Prunus species, supporting our hypothesis. The combination and inheritance of chromosomal segments corresponding to the LOH-region within Japanese peaches will be discussed.