Pradillo, M. | bioRxiv Science

bioRxiv2024

Genetic dissection of MutL complexes in Arabidopsis meiosis

During meiosis, homologous chromosomes exchange genetic material through crossing-over. The main crossover pathway relies on ZMM proteins, including ZIP4 and HEI10, and is typically resolved by the MLH1/MLH3 heterodimer, MutL{gamma}. Our analysis of plant fertility and bivalent formation revealed that the MUS81 endonuclease can partially compensate for the MutL{gamma} loss. Comparing genome-wide crossover maps of the mlh1 mutant with ZMM-deficient mutants and lines with varying HEI10 levels reveals that while crossover interference persists in mlh1, it is weakened. Additionally, mlh1 show reduced crossover assurance, leading to a higher incidence of aneuploidy in offspring. This is likely due to MUS81 resolving intermediates without the crossover bias seen in MutL{gamma}. Comparing mlh1 mlh3 mus81 and zip4 mus81 mutants suggests that additional crossover pathways emerge in the absence of both MutL{gamma} and MUS81. The loss of MutL{gamma} can also be suppressed by eliminating the FANCM helicase. Elevated expression of MLH1 or MLH3 increases crossover frequency, while their overexpression significantly reduces crossover numbers and plant fertility, highlighting the importance for tight control of MLH1/MLH3 levels. By contrast, PMS1, a component of the MutL endonuclease, appears not to be involved in crossing-over. Together, these findings demonstrate the unique role of MutL{gamma} in ZMM-dependent crossover regulation.

genetics↗

bioRxiv2024

PDS5s control the Arabidopsis 3D genome by suppressing the formation of TAD-like domains

One key structural element in the three-dimensional (3D) chromatin organization is the Topologically Associating Domain (TAD), which facilitates the formation of distinct chromatin compartments and fosters specific chromatin interactions. Similar chromatin compartments, known as TAD-like domains, have been identified in many plant species. However, the model plant Arabidopsis thaliana has been an exception. In this study, we address this long-standing issue by presenting evidence that Arabidopsis PDS5 proteins play a crucial role in preventing the formation of TAD-like domains.

molecular biology↗

bioRxiv2022

The Arabidopsis Hop1 homolog ASY1 mediates cross-over assurance and interference

The chromosome axis plays a crucial role in meiotic recombination. Here, we study the function of ASY1, the Arabidopsis homolog of the yeast chromosome axis associated component Hop1. Specifically, we characterized cross-over (CO) distribution in female and male meiosis by deep sequencing of the progeny of an allelic series of asy1 mutants. Combining data from nearly 1000 individual plants, we find that reduced ASY1 activity leads to genomic instability and sometimes drastic genomic rearrangements. We further observed that COs are less frequent and appear in more distal chromosomal regions in plants with no or reduced ASY1 activity, consistent with previous analyses. However, our sequencing approach revealed that the reduction in CO number is not as dramatic as suggested by cytological analyses. Analysis of double mutants of asy1 with mutants with three other CO factors, MUS81, MSH4 and MSH5 as well as the determination of foci number of the CO regulator MLH1 demonstrates that the majority of the COs in asy1, similar to the situation in the wildtype, largely belong to the class I, which are subject to interference. However, these COs are redistributed in asy1 mutants and typically appear much closer than in the wildtype. Hence, ASY1 plays a key role in CO interference that spaces COs along a chromosome. Conversely, since a large proportion of chromosomes do not receive any CO, we conclude that CO assurance, the process that ensures the obligatory assignment of one CO per chromosome, is also affected in asy1 mutants. Significant statementThe regulation of the number and placement of cross-overs (COs) during meiosis is critical to ensure meiotic fidelity and promote new genetic combinations. Here, we investigated the function of one of the proteins of the chromosome axis, which plays a key role in CO formation: ASY1. Our results show that COs in asy1 mutants are positioned closer to each other than in the wildtype and that, despite a roughly similar number of COs, not every chromosome receives a CO. With this, our results shed light on the mechanisms regulating two important but still poorly understood aspects of meiosis: CO assurance, which safeguards at least one CO per chromosome pair, and CO interference, which prevents two COs from occurring close to each other.

cell biology↗