Year: 2025
Type: conference-paper
Abstract: When heterozygous chromosome regions alternate with heterozygous ones, the juxtaposition effect appears at the joints: crossovers are redistributed from homozygous regions to neighboring heterozygous ones. It is easier to observe an increase in the recombination frequency (RF) in heterozygous regions than a decrease in homozygous ones, since in the first case it is possible to measure the RF using morphological markers. In our work, alternation of homo- and heterozygous intervals was ensured by hybridization of two closely related maize lines, one of which (isogenic) differs from the other (original) by a marked fragment transferred from the 2-9m line. The fragments ws3-lg1, lg1-gl2 (chromosome 2) and c1-sh1, sh1-wx1 (chromosome 9) were transferred to genetic background of the MK01 and Ku123 lines. In hybrids of isogenic lines with the original ones, stimulation of crossovers was observed: the RF between markers increased by 1.5-3 times compared to the control - a complete heterozygote along the entire chromosome. In further studies, some factors influencing the manifestation of this effect were revealed. First of all, this is the length of the heterozygous fragment. The farther the homo/hetero boundaries are from the edge markers, the lower RF, and at a sufficient distance RF decreases to the control level. For example, a fragment containing the marker pair lg1-gl2 was transferred to the genetic background Ku123 and MK01. In the first case, introgression was accurate, and in the second case, a 7 Mb region to the left of the lg1 locus was transferred along with the markers. As a result, the stimulation of crossovers was 2-2.5 in the first case and 1.4 in the second. This suggests that crossover redistribution has a limited range and fades with distance from the homo/hetero boundary. Furthermore, crossovers can be recruited only from recombination-active regions, as was observed for the sh1-wx1 interval. The right wx1 locus is adjacent to the recombination-silent pericentromeric zone, and the accuracy of introgression near the wx1 was not important: in one case, introgression was accurate, in the other case, an extra 7 Mb fragment on the right was captured. In both the cases, the stimulation of crossovers was 2.2-2.7. Finally, the heterozygous interval must be continuous. When a short homozygous block of 6 Mb was introduced into the ws3-gl2 heterozygous interval, the juxtaposition effect completely disappeared. The juxtaposition effect is manifested in both male and female meiosis. As for the required level of polymorphism in heterozygous regions, in our experiments 0.5 SNP/kb was enough to manifest the effect. It is unknown how widespread the juxtaposition effect is among plants. So far, it has been observed only in maize and Arabidopsis. These are very distant and dissimilar species: maize is a monocot outcrosser, Arabidopsis is a dicot selfpollinator, and they are separated by 140 million years of evolution. It is possible that the juxtaposition effect arose in them independently, but it is possible that it was inherited from a common ancestor. In this case, this effect could be preserved in many other species, which should be verified by further research.
Author: Mihai Mihailov
Institution: Moldova State University
Language: English
Subfield: Genetics
Domain: Life Sciences
SDG: Zero hunger
Open Access status: bronze
OpenAlex ID: W7204682843