A unique chiasmata formation observed in a certain type of Allium monosomic addition lines and estimation of its causal genes

There is a difference in the mode of chiasma formation between Allium cepa (AA) and A. fistulosum (FF). Allium cepa forms randomized chiasmata (ring-shaped), A. fistulosum forms localized chiasmata (cross-shaped). We tried to reveal the expression mechanism of this phenotype by conducting cytogenetic observation and differential expression analysis of chromosome pairing-associated transcriptomes in alien monosomic addition lines.
Eight kinds of A. fistulosum–A. cepa monosomic additions (FF+1A-FF+8A; 2n=2x+1=17) were used as plant materials for observing chromosome pairings at meiotic metaphase-I in the PMCs during flowering in spring 2020 and 2021. More than 80% of the bivalents derived from A. fistulosum formed localized chiasmata in most types of the monosomic additions.
In FF+2A, almost half of the chiasmata were found in the interstitial or distal sites of the bivalent.
This indicated that the factor to control the mode of chiasma formation is located on 2A chromosome of A. cepa. In a search for genes involved in the phenotype specific to the bivalents of FF+2A, the transcriptome differential expression analysis was carried out by using two ring-shaped lines (AA, FF+2A) and two cross-shaped lines (FF, FF+1A) in three different floret growth stages.
RNA-seq analyses were performed on the various-sized florets from these four lines with three biological replicates, yielding an average of 24 M reads from each sample.
Mapping the obtained reads using the unigene sequence of A. cepa as references allowed comparison of the transcript expression levels in each sample.
Finally, around 60 transcripts were selected as the common denominators of the three stages.
The annotation information of those genes was confirmed, and a gene, an anti-crossover factor, was included.
This gene was considered a candidate factor responsible for the establishment of the ring-shaped chiasma formation.

IV Asian Horticultural Congress – AHC2023

Y. Shimomi, S. Sato, T. Nakajima, L. Khrustaleva, J. Duangjit, M. Shigyo

chiasma, Allium cepa, A. fistulosum, alien monosomic addition line

https://doi.org/10.17660/ActaHortic.2024.1404.80