Knl1 participates in spindle assembly checkpoint signaling in maize

Abstract

The Knl1-Mis12-Ndc80 (KMN) network is an essential component of the kinetochore–microtubule attachment interface, which is required for genomic stability in eukaryotes. However, little is known about plant Knl1 proteins because of their complex evolutionary history. Here, we cloned the Knl1 homolog from maize (Zea mays) and confirmed it as a constitutive central kinetochore component. Functional assays demonstrated their conserved role in chromosomal congression and segregation during nuclear division, thus causing defective cell division during kernel development when Knl1 transcript was depleted. A 145 aa region in the middle of maize Knl1, that did not involve the MELT repeats, was associated with the interaction of spindle assembly checkpoint (SAC) components Bub1/Mad3 family proteins 1 and 2 (Bmf1/2) but not with the Bmf3 protein. They may form a helical conformation with a hydrophobic interface with the TPR domain of Bmf1/2, which is similar to that of vertebrates. However, this region detected in monocots shows extensive divergence in eudicots, suggesting that distinct modes of the SAC to kinetochore connection are present within plant lineages. These findings elucidate the conserved role of the KMN network in cell division and a striking dynamic of evolutionary patterns in the SAC signaling and kinetochore network.

Disruption of the standard kinetochore in holocentricCuscutaspecies

“…(Left) The architecture of the plant SAC differs from that in animals/yeasts 47,48,68,69 , and the function and interactions of some SAC proteins are not yet known (dashed lines with question marks). (Right) Plant KNL1 lacks MELT, KI1, and KI2 domains and binds BMF1 and BMF2 proteins via the BMF domain near the C-terminus 48 . d , SAC and KNL1 in holocentric Cuscuta species.…”

“…Structural and regulatory kinetochore protein sequences identified in A. thaliana were downloaded from uniprot database and from published studies [47][48][49] . These sequences were used for blastp searches to identify their homologs in genome assemblies of C. australis and C. campestris 50,51 , representing monocentric Cuscuta species, and in I. nil 52 , selected as a monocentric nonparasitic genus of the family Convolvulaceae.…”

Microtubule Regulation in Plants: From Morphological Development to Stress Adaptation

“…Plants have conserved the SAC network with some variations from animals and yeast [ 67 ]. The dissection of proteins associated with SAC led to the discovery of novel aspects of plant SAC regulation [ 68 , 69 ], which may be relevant for plant breeding studies because ploidy alternations likely rely on SAC properties.…”

Heat stress at the bicellular stage inhibits sperm cell development and their transport into pollen tubes

“…Moreover, plant cells are able to reset the cell cycle with duplicated chromosomes avoiding nuclear division (Kozgunova et al, 2019). In maize, some of the major components of the SAC have been identified and showed conserved function (Yu et al, 1999; Du and Dawe, 2007; Li and Dawe, 2009; Su et al, 2021), but it is unclear whether SAC plays also a role in PM II. Reduction in fertilization success and yield due to defects in male gametophyte performance have been largely attributed to the lack of pollen viability or inability to germinate under high temperatures (Firon et al, 2006; Endo et al, 2009; De Storme and Geelen, 2014; Wang et al, 2017; Begcy et al, 2018; Begcy et al, 2019).…”