The composition and structure of the outer kinetochore KMN complex is conserved across kingdoms

TL;DR

The study shows that the KMN complex, important for chromosome segregation, is conserved across different eukaryotic kingdoms, including plants.

Contribution

The discovery of thirteen KMN proteins in Arabidopsis, including six uncharacterized ones, reveals conservation across distant eukaryotes.

Findings

Affinity purification identified thirteen KMN proteins in Arabidopsis, seven of which were previously known.

Six newly identified proteins show remote similarity to known KMN-associated proteins and are essential for kinetochore function.

AlphaFold3 predicts a similar 3D organization of the KMN complex in plants and mammals.

Abstract

In eukaryotes, chromosome segregation relies on attachment to the spindle, ensured by the kinetochore. The outer kinetochore attaches to the microtubules and is named after three sub-complexes KNL1C, MIS12C, and NDC80C (KMN). While the KMN complex comprises ten proteins in humans S. cerevisiae, its conservation in more distant eukaryotes is unclear. Here, we aimed to define the KMN complex in the plant Arabidopsis using affinity purification and identified thirteen KMN proteins. Seven were previously known to have a conserved function (atMIS12, atNNF1, atNDC80, atSPC24, atSPC25, atNUF2, and atKNL1) and six were uncharacterized. These six proteins show remote similarity to yeast/human KMN-associated proteins, whose homologs have not yet been characterized in plants. We named them atDSN1, atCSM1, atNSL1.1/.2, and atZWINT1.1/.2. We confirmed kinetochore localization for atDSN1, atCSM1, atNSL1.1, and atZWINT1.1 in planta. In addition, atDSN1, atCSM1, and ZWINT1.1/.2 are essential, further supporting their kinetochore function. AlphaFold3 predicts an alike3D organization of the KMN complex in plants and mammals. We conclude that the KMN complex is globally conserved with a matching composition and similar organization in distant eukaryotes, with some local variations, suggesting its presence in the common ancestors of all living eukaryotes.

Affinity purification in Arabidopsis identified all key subunits of the outer kinetochore KMN complex. Functional analyses revealed a striking conservation of its composition and organization across kingdoms, underscoring its deep evolutionary origin.

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