NUP1/NUP136 is essential for obligatory crossover formation during meiosis in <i>Arabidopsis</i>

The nuclear pore complex (NPC) is a major component of the nuclear envelope (NE), which mediates nucleocytoplasmic transport and is involved in a variety of transport-independent processes, including genome organization and cell division. In plants, several NPC subunits are species specific, and their roles in meiosis remain poorly understood. Here, we characterize the function of the plant-specific nuclear basket nucleoporin NUP1/NUP136 during meiosis in Arabidopsis thaliana. Loss of NUP136 leads to a marked reduction in chiasma frequency, resulting in univalents, and the persistence of chromosome interlocks at metaphase I. This phenotype is consistent with defects in early chromosome interactions and crossover (CO) formation, as evidenced by a reduced number of MLH1 foci. In the mutant, there is also an altered spatial distribution of centromeres, telomeres, and nucleolar organizer regions (NORs), pointing to changes in the dynamics of these chromosomal domains during meiotic prophase I. Meiotic defects in nup136-2 mutants are modestly aggravated by the loss of the related paralog NUP82. Our results demonstrate that NUP1/NUP136 is important for proper homologous chromosome pairing and for ensuring the formation of the obligatory CO, likely by contributing to NE organization and facilitating the chromosomal contacts that support recombination during prophase I.